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Using Arduino => Project Guidance => Topic started by: David82 on Jan 05, 2013, 08:49 pm

Title: How do I prevent video interference caused by electric motors
Post by: David82 on Jan 05, 2013, 08:49 pm
I have an analog camera signal, the power for the camera, and a dc motor which is activated by a switch and all share the same ground. When the motor is activated, the video feed blanks out for a second. I tried putting a capacitor on the + - rail but that didn't do anything. What can be added to this circuit to prevent the video signal from being interfered with?


In the illustration below, when the switch/button is pressed, the lcd screen blanks out because some sort of interference is being caused but the presence of the electric motor. This interference happens when the motor is switched on and under load AND when again when it is switched off but not while it is on! I can't change the wiring but I can add something to the circuit to filter out the interference somehow. What can be added to this circuit to prevent the video signal from being interfered with?

(http://i.imgur.com/S1bfU.png)
Title: Re: How do I prevent video interference caused by electric motors
Post by: zoomkat on Jan 05, 2013, 08:55 pm
Quote
I can't change the wiring but I can add something to the circuit to filter out the interference somehow. What can be added to this circuit to prevent the video signal from being interfered with?


If you can't change the wiring, then try using a larger power supply. 
Title: Re: How do I prevent video interference caused by electric motors
Post by: David82 on Jan 05, 2013, 09:01 pm
what is actually happening to cause the interference (besides the motor being activated)? I don't think the video camera is losing power. It seems that the signal is being corrupted temporarily.
Title: Re: How do I prevent video interference caused by electric motors
Post by: larryd on Jan 05, 2013, 09:16 pm
Try:
Title: Re: How do I prevent video interference caused by electric motors
Post by: Grumpy_Mike on Jan 05, 2013, 09:20 pm
Quote
what is actually happening to cause the interference

Current flowing in a conductor when it has a fast rise time radiates radio frequency energy. As a current pulse has an infinite number of harmonics it radiates a broad band interference signal.

Quote
can't change the wiring

So you are probably stuffed.
However, you can try and cut down the interference by reducing the rise time in the motors by using capacitors close up to the motor contacts. You could change the motor type so that it does not have a commutator circuit breaker or you could attempt to minimise the disruptive effect of the interference in your video circuits by increasing supply decoupling. The "larger supply" solution works because it is a lower impedance supply and so less prone to picking up the signal.
However curing the problem at source is often a much better strategy.
Title: Re: How do I prevent video interference caused by electric motors
Post by: David82 on Jan 05, 2013, 09:24 pm
Quote
Current flowing in a conductor when it has a fast rise time radiates radio frequency energy.

Can't I shield against it with a faraday cage of some sort?
Title: Re: How do I prevent video interference caused by electric motors
Post by: Grumpy_Mike on Jan 05, 2013, 09:32 pm
Quote
Can't I shield against it with a faraday cage of some sort?

No. You have to get the signals in and out and that breaks the cage effect.

Your wiring is bad if you could improve that it would help matters. Use a star ground wiring system not what you have at the moment.
Title: Re: How do I prevent video interference caused by electric motors
Post by: zoomkat on Jan 05, 2013, 09:43 pm
Quote
I don't think the video camera is losing power. It seems that the signal is being corrupted temporarily.


What is your power supply? If the motor starting current is high, it may cause the voltage to dip low until the motor comes up to speed.
Title: Re: How do I prevent video interference caused by electric motors
Post by: David82 on Jan 05, 2013, 09:47 pm

Quote
I don't think the video camera is losing power. It seems that the signal is being corrupted temporarily.


What is your power supply? If the motor starting current is high, it may cause the voltage to dip low until the motor comes up to speed.
If that was the case, the giant capacitor I tried to fix it with would've had some effect I would think.
Title: Re: How do I prevent video interference caused by electric motors
Post by: David82 on Jan 05, 2013, 09:57 pm
Applying a charged capacitor to the circuit will also cause the same temporary interference. What does that mean?
Title: Re: How do I prevent video interference caused by electric motors
Post by: zoomkat on Jan 05, 2013, 09:57 pm
Quote
If that was the case, the giant capacitor I tried to fix it with would've had some effect I would think.


Not really. The motor start can still pull the voltage low with a capacitor. Depending on the motor, the motor starting current can be several amps. So what is your power supply?
Title: Re: How do I prevent video interference caused by electric motors
Post by: David82 on Jan 05, 2013, 10:00 pm
It's a 90W computer power supply and the motor is a power door lock actuator.
Title: Re: How do I prevent video interference caused by electric motors
Post by: Grumpy_Mike on Jan 05, 2013, 10:03 pm
Quote
Applying a charged capacitor to the circuit will also cause the same temporary interference. What does that mean?

It means you do not have any idea about fault finding.

Stop asking the same question and start reading the answers.
Title: Re: How do I prevent video interference caused by electric motors
Post by: David82 on Jan 05, 2013, 10:13 pm
I added a second, 12v power supply to the camera's power just to see what effect it might have. It shopped it from completely blacking out but there was still a little bit of interference. So basically it improved it but didn't solve it. Of course I can't use that in the final design but does that give any clues as to what needs to be added to fix the problem?
Title: Re: How do I prevent video interference caused by electric motors
Post by: Grumpy_Mike on Jan 05, 2013, 10:21 pm
If you are not going to read the answers then I am not going to tell you again.
Good night.
Title: Re: How do I prevent video interference caused by electric motors
Post by: David82 on Jan 05, 2013, 10:36 pm
I read the answers. I tried the diode wiring diagram but that had no effect. The other answers contained no specific instructions that fit the working parameters of this project (can't change wiring, can't change power supply) so they aren't of any help. I can add things to the project like capacitors, diodes, inductors, etc.

The right answer would be something like, "oh, I've come across this specific problem a lot. I found that all you had to do was add x, y, z components at p location in your diagram and that will prevent the problem."
Title: Re: How do I prevent video interference caused by electric motors
Post by: HazardsMind on Jan 05, 2013, 10:48 pm
Quick question, does the actuator go forward and backwards or just one direction? Your drawing shows that it is only going in one direction.

I wonder if your motors outer casing is shielded? If its not, that might cause the interference.

This is what I mean, I can't find a better picture at the moment, sorry. EDIT: picture link didn't work

Actual link http://letsmakerobots.com/node/22353 (http://letsmakerobots.com/node/22353)


Title: Re: How do I prevent video interference caused by electric motors
Post by: oric_dan on Jan 05, 2013, 11:09 pm
Quote
The right answer would be something like, "oh, I've come across this specific problem a lot. I found that all you had to do was add x, y, z components at p location in your diagram and that will prevent the problem."

Your biggest problem is that, G_M told you many fixes according to "good" design, but you kept
saying you are too constrained to use them. You have to keep with a crappy design. That's #1.

And #2 is that you expect ONE little thing to magically fix the problem, whereas these sorts
of troubles generally require adding essentially many or all the fixes already recommended.
Each has it's own reason, and share of the burden.

My recommendation is you start over, and do it right. Otherwise, just keep trying different
1/off fixes and maybe you'll find something to work. Also, check the links at the bottom post
#8 here,

http://arduino.cc/forum/index.php/topic,140455.0.html

Title: Re: How do I prevent video interference caused by electric motors
Post by: David82 on Jan 05, 2013, 11:40 pm
I'm really surprised that this is such a hard thing to fix. I had a similar problem where a electric motor from an airsoft gun was causing interference in the boards inside of hobby servos. This interference would cause them to jolt each time the motor made the gun fire. This was simply solved however by adding 2 capacitors spread along the power leads going to the gun and maximizing the distance between the gun motor and the servo. This is the same kind of thing but now dc motors are interfering with an analog video feed instead.

Even after reading all of this, I still don't know if the problem is RF interference, or drastic voltage drops/spikes. Gotta know that first to be able to move forward...
Title: Re: How do I prevent video interference caused by electric motors
Post by: HazardsMind on Jan 05, 2013, 11:51 pm
If your not sure if the voltage is dropping or not, use a volt meter to confirm that. However, you did say that you put the video monitor on a different power supply and it did nothing, SO maybe voltage drop is not the problem. You are most likely having a shielding issue. Do like G_Mike says, and rewire it correctly.

If you want another way to test the RF from the motor, is to simply use an AM radio. Set the radio to a clear station, and try to turn the motor on and off. If you get interference when the motor is on, then you need to shield the motor. My guess is the motors metal casing is not shielded. What you can try is run the motor with the radio on, then use a wire to touch the metal casing to ground. If the interference goes away then you know you have a shielding issue.
Title: Re: How do I prevent video interference caused by electric motors
Post by: David82 on Jan 06, 2013, 12:07 am

If your not sure if the voltage is dropping or not, use a volt meter to confirm that. However, you did say that you put the video monitor on a different power supply and it did nothing, SO maybe voltage drop is not the problem. You are most likely having a shielding issue. Do like G_Mike says, and rewire it correctly.

If you want another way to test the RF from the motor, is to simply use an AM radio. Set the radio to a clear station, and try to turn the motor on and off. If you get interference when the motor is on, then you need to shield the motor. My guess is the motors metal casing is not shielded. What you can try is run the motor with the radio on, then use a wire to touch the metal casing to ground. If the interference goes away then you know you have a shielding issue.


My multimeter is digital and it doesn't react anywhere near fast enough to tell me if the voltage drops :(

The motor just turns for half a second since it is just a power door lock actuator. It just extends or contracts an arm. Will that be long enough of a duration to try the AM radio test? Also, the same brief interference problem was experienced just by applying a charged capacitor to the circuit.
Title: Re: How do I prevent video interference caused by electric motors
Post by: rvasque on Jan 06, 2013, 12:13 am
Quote
The right answer would be something like, "oh, I've come across this specific problem a lot. I found that all you had to do was add x, y, z components at p location in your diagram and that will prevent the problem."


You're living in a dream world if you think it's just like that.

RF and EMI interference can be tricky to solve.

For one thing, your prototype isn't running on a "proper" PCB... double-sided, lots of ground plane, bypass capacitors, etc... your prototype is a spaghetti of wires. Expect RF/EMI problems.  Putting your design on a PCB, with doublesided ground planes will fix majority of noise problems.-- of course proper layout and component placement is also a must.

Second, sometimes it's trial and error. If you don't know the frequency(ies) of the interference, then you can try different value capacitors. (Even engineers doing testing in Anechoic RF testing chambers have different value caps with them as they try to hunt their RF problems.)

You need both a big value cap and maybe 1 or more small value caps... 220uf, 47uf 10uf, 0.1uf, .01uf, 100pf... in parallel on the V+/V- supply lines (preferably for each chip).

For example, this is just a simple RC circuit... without a capacitor (or the wrong value capacitor), the graph is like this: ckt1.png

Imagine there's interference happening in the 5-10Mhz band.

Now, changing the value of the capacitor, the response is dramatically changed. ckt2.png
Look at the same 5-10Mhz band. If you have any interference happening in that band, this value of capacitor will reduce it.

Third, your project isn't in a proper metallic case. It's not even grounded. Yes, it will be barfing RF like crazy.

There is no single magic pill in solving RF problems. It's like "water"... even one tiny leak, one weak spot in your design, and RF gushes out of that hole. (There are special cases that are RF shielded, with protective gaskets and screens around hole openings, etc...)
Title: Re: How do I prevent video interference caused by electric motors
Post by: David82 on Jan 06, 2013, 12:24 am
I tried using an am radio right next to the project. Only on the lowest, static, AM frequency could I hear different pitches as I activated the motor. More importantly, I found that a motor that was also being used in this project, (that uses a motor controller and doesn't interfere with the video signal), makes a louder pitch in the radio. Basically I'm saying that one of the motors that doesn't cause any problems is actually a lot louder than the one that does. Both are pretty quiet though.
Title: Re: How do I prevent video interference caused by electric motors
Post by: HazardsMind on Jan 06, 2013, 12:25 am
So wait, you were listening for static changes on a channel that already had static? -_^ Use a static free channel, then use the motor.

Just try grounding the motors metal casing. If it doesn't solve it, at least to you tried something. What would be more helpful is if you show us an actual picture or video of your setup. Show us your wiring.

Give us something, otherwise were not going to continue to help you.
Title: Re: How do I prevent video interference caused by electric motors
Post by: zoomkat on Jan 06, 2013, 12:49 am

It's a 90W computer power supply and the motor is a power door lock actuator.


Is it a dual output power supply (like 5v and 12v)? If so, the 12v output rating may be less than the 90w overall rating. Back in the day computer power supplys supplied 5v with high amp ratings, and 12v at low amp ratings, as the 12v only powered the cooling fan and such.
Title: Re: How do I prevent video interference caused by electric motors
Post by: David82 on Jan 06, 2013, 12:51 am
yup, but I still need a definitive test that tells me that the problem is too much voltage fluctuation. It happens to fast too be detected on my digital meter..

Remember, the same brief interference problem was experienced just by applying a charged capacitor to the circuit. That should be a really helpful clue.
Title: Re: How do I prevent video interference caused by electric motors
Post by: zoomkat on Jan 06, 2013, 01:24 am
Quote
yup, but I still need a definitive test that tells me that the problem is too much voltage fluctuation. It happens to fast too be detected on my digital meter...


Shows the value of keeping a cheap undampened $10 analog meter handy. I don't see an arduino in your circuit, so why don't you use your arduino to test for a low voltage condition? Use a pot as a voltage divider, connecting the pot output across the 12v supply, and adjusting the wiper output to 5v to supply an analog input pin on the arduino. write code that will print out values if the wiper voltage drops by something like 70%. You could also use an automotive bulb across the power supply to see if it dims when the motor starts. If you can't change the wiring, then you need a better power supply.
Title: Re: How do I prevent video interference caused by electric motors
Post by: David82 on Jan 06, 2013, 01:25 am
I just did an experiment that produced interesting results. If I introduce a second power supply that shares the same ground, and use that to actuvate the power door lock motor, the video loss problem is gone. What's nice about this experiment is that it rules out RF interference. I'm not sure what to do with this new info yet because I can't add another power supply but I should be able to figure it out now.
Title: Re: How do I prevent video interference caused by electric motors
Post by: oric_dan on Jan 06, 2013, 02:07 am
Quote
If I introduce a second power supply that shares the same ground, and use that to actuvate the power door lock motor, the video loss problem is gone.


Now, you're starting to get to where G_M mentioned "Use a star ground wiring system not
what you have at the moment" in post #6, and which is also discussed in the 1st link I gave.
If you read the part where is says "Main capacitor" in the 2nd link, you'll learn some more.
Title: Re: How do I prevent video interference caused by electric motors
Post by: David82 on Jan 06, 2013, 02:59 am
so what specifically needs to change in my original 'wiring diagram' so that it becomes a star ground wiring system?
Title: Re: How do I prevent video interference caused by electric motors
Post by: zoomkat on Jan 06, 2013, 03:05 am
Quote
so what specifically needs to change in my original 'wiring diagram' so that it becomes a star ground wiring system?


This will be interesting to see what changes, as all the grounds seem connected. If you can change your wiring which you said you couldn't) then there may be other solutions.
Title: Re: How do I prevent video interference caused by electric motors
Post by: David82 on Jan 06, 2013, 03:11 am
it's only when the power door lock motor is on it's own battery power supply that the problem goes away.
Title: Re: How do I prevent video interference caused by electric motors
Post by: zoomkat on Jan 06, 2013, 03:31 am
Quote
it's only when the power door lock motor is on it's own battery power supply that the problem goes away.


Bummer
Title: Re: How do I prevent video interference caused by electric motors
Post by: David82 on Jan 06, 2013, 03:49 am
yea, that doesn't help. How do you simulate two separate power supplies using one?
Title: Re: How do I prevent video interference caused by electric motors
Post by: oric_dan on Jan 06, 2013, 03:53 am
Quote
so what specifically needs to change in my original 'wiring diagram' so that it becomes a star ground wiring system?

Look in the link I've pointed you at twice now.
Title: Re: How do I prevent video interference caused by electric motors
Post by: David82 on Jan 06, 2013, 05:36 am

Quote
so what specifically needs to change in my original 'wiring diagram' so that it becomes a star ground wiring system?

Look in the link I've pointed you at twice now.

ok. I read it. It talked about using a main capacitor to absorb voltage spikes and drops. I tried using a 1000uF, 35v cap. It didn't have any effect. So, back to where we left off at. It flickers even when a charged cap is applied, it doesn't flicker when a the power door lock is being powered by batteries that share the same ground as the original power supply. Given these clues, what specific tests can be performed to find out what needs to be added to calm the voltage or current? What about an inductor? Maybe the capacitor isn't large enough?
Title: Re: How do I prevent video interference caused by electric motors
Post by: zoomkat on Jan 06, 2013, 08:16 am
Quote
Look in the link I've pointed you at twice now.


I looked at the single link i see posted that led to other links, and in a quick scan of the resultant pages didn't see anything helpful to the current issue (well maybe if a capacitor the size of a microwave oven is used). If the OP can't change the power supply or make any modifications to his current setup, his project is toast. It is what it is, and no amount of wishful thinking will change that fact. The laws of physics generally ignore fantasy thinking.
Title: Re: How do I prevent video interference caused by electric motors
Post by: dc42 on Jan 06, 2013, 12:28 pm
If you want to run both the motor and the battery from the same 12V supply, then at the very least the motor should have its own power and ground cables between the it and the power supply. Do not share any part of the motor power or ground lines with the power feed to the video camera. But this probably won't be sufficient, because switch mode power supplies don't react instantaneously to large changes in load current.

1000uF is probably nothing like large enough to supply the current peak when the motor starts up. 20000uF would be more like it.

Consider adding slow-start to the motor. This will reduce the current surge when it switches on and give the power supply time to react. One way is to replace the switch with a mosfet, and feed the mosfet with a slowly-increasing PWM signal. Don't forget to put a diode across the motor if you do this. Similarly, use slow-stop.
Title: Re: How do I prevent video interference caused by electric motors
Post by: David82 on Jan 06, 2013, 01:20 pm
What you're saying makes a lot more sense and matches the results I get through experimentation. Wouldn't an inductor of the right size smooth out current spikes and solve it?
Title: Re: How do I prevent video interference caused by electric motors
Post by: dc42 on Jan 06, 2013, 01:31 pm

Wouldn't an inductor of the right size smooth out current spikes and solve it?


An LC filter between the power supply and the motor, and/or between the power supply and the video camera, would fix it. But the inductor needed would be very large, so I don't think this is a practical solution.
Title: Re: How do I prevent video interference caused by electric motors
Post by: David82 on Jan 07, 2013, 03:06 am
wow. I've been messing with this for days now and tried so many things. Is there someone I can pay to solve it with the constraints I mentioned?

Here is the challenge:
(http://i.imgur.com/RJOjM.png)
while everything is powered on and working, connect an uncharged capacitor, motor, or any other device that draw significant current to terminal A, with any additional components, such that the video feed does not flicker. You cannot change the wiring. Everything shares a ground as illustrated including the ground portion of the video feed.
Title: Re: How do I prevent video interference caused by electric motors
Post by: HazardsMind on Jan 07, 2013, 04:18 am
Can you make a list of how much current and voltage your components use, like what they are rated for VS what your able to supply? Also a visual picture and/or video would be helpful too.

And if you want to pay someone to do this for you, you need to make a post in "Gigs and Collaborations".
Title: Re: How do I prevent video interference caused by electric motors
Post by: David82 on Jan 07, 2013, 04:44 am
ok, I'll post in there too. It seems like this problem will occur throughout a WIDE range of possible component specs (amp draw, voltage etc.) making that question not only very hard to answer, but largely irrelevant. I'll humor the idea anyway though. the power supply is a 90W computer power supply. All sorts of stuff can be hooked up to terminal A to make the video flicker so specs on that don't exist. The specs on the camera and LCD screen are unknown and don't seem to be relevant anyway..

This problem should be immediately recognizable to someone with the proper experience.
Title: Re: How do I prevent video interference caused by electric motors
Post by: zoomkat on Jan 07, 2013, 04:50 am
Quote
This problem should be immediately recognizable to someone with the proper experience.


Sure, you most likely have an inadequate power supply.
Title: Re: How do I prevent video interference caused by electric motors
Post by: David82 on Jan 07, 2013, 04:58 am
The same effect is seen even when using 8AA batteries instead of the pc power supply :/
Title: Re: How do I prevent video interference caused by electric motors
Post by: zoomkat on Jan 07, 2013, 05:11 am

The same effect is seen even when using 8AA batteries instead of the pc power supply :/


The wires from the power supply may be too small to pass sufficient starting current to the motor resulting a brownout of the camera. Particulalry if your AA batterys are in one of those radio shack battery holders, that could be an issue.  If the cam could operate at 11v instead of 12v, then a diode in the cam + wire with a big capacitor between the diode and the cam, your problem might be solved. If you can't change any thing, then note the below.

Quote

Insanity: doing the same thing over and over again and expecting different results.
Albert Einstein
Title: Re: How do I prevent video interference caused by electric motors
Post by: oric_dan on Jan 07, 2013, 05:17 am
Quote
a quick scan of the resultant pages didn't see anything helpful to the current issue (well maybe if a capacitor the size of a microwave oven is used). If the OP can't change the power supply or make any modifications to his current setup, his project is toast.

Maybe a more through scan would help too. First off, it describes the use of star grounding
that G_M originally mentioned. If properly implemented, this helps keeps the motor current
noise from getting onto the power and ground leads of the video ckt.

Secondly, the Main Capacitor needs to be placed correctly [as indicated on the link cited], and
its job is to help compensate for the inductance of overly long leads [meaning more than a
couple of inches] from the battery/power supply to the board being powered. It probably won't
help much if the motor load is so great it shorts the buss temporarily, or if it's located in
the wrong place.

Thirdly, it was pointed out back in reply #17, and probably also by others, that what OP has
been trying to do all along is find one patch/fix for a crappy design, rather than build a
better design from the getgo. Further, he seems intend on abandoning every "fix" that
doesn't solve the problem completely, whereas he's been told that a good design has many
aspects, not just one bit of magic.

Fourthly, the reason for pointing OP to the links in the first place was because some of
us don't believe in simply spoon-feeding proverbial loaves'n'fishes to neophytes. Ultimately,
the object is to learn something about what you're doing.

Fifthly, relative to item #4, it might be helpful to look up the concept of "Cargo Cult". See
especially "In an attempt to attract further deliveries of goods, followers of the cults engaged
in ritualistic practices such as building crude imitation landing strips, aircraft and radio
equipment, and mimicking the behavior that they had observed of the military personnel
operating them".

http://en.wikipedia.org/wiki/Cargo_cult

See also,
http://en.wikipedia.org/wiki/Cargo_cult_science
http://en.wikipedia.org/wiki/Cargo_cult_programming
Title: Re: How do I prevent video interference caused by electric motors
Post by: zoomkat on Jan 07, 2013, 05:46 am
My only suggestion now for the OP is to start making sacrifices to some diety. I suggest starting with a 20 piece bucket of KFC extra crispy. Below is how I brownout protected a servo control chip back in the day.

(http://web.comporium.net/~shb/pix/ezservo.jpg)
Title: Re: How do I prevent video interference caused by electric motors
Post by: David82 on Jan 07, 2013, 06:01 am


The wires from the power supply may be too small to pass sufficient starting current to the motor resulting a brownout of the camera. Particulalry if your AA batterys are in one of those radio shack battery holders, that could be an issue.  If the cam could operate at 11v instead of 12v, then a diode in the cam + wire with a big capacitor between the diode and the cam, your problem might be solved. If you can't change any thing, then note the below.



That's a good suggestion. I tried moving the batt pack right up to the camera power leads but still had the same issue. remember, even just placing a uncharged cap anywhere on the + - rails will still cause the momentary camera blackout.

Ideally, the problem would go away if I didn't have to have all of the ground leads connected together. I could use two power supplies to completely isolate the camera power from everything else so that it's power wouldn't be interfered with. That's not possible with this design so i need to simulate the same thing. I need to make it so that the camera power is unable to experience any voltage drops or spikes and the same with current.
Title: Re: How do I prevent video interference caused by electric motors
Post by: HazardsMind on Jan 07, 2013, 03:03 pm
Does you door lock, stay energized? If so, it might be putting on additional resistance to your battery, which will want to eat up more current from the battery. If it is doing this, it could be taking current from the camera.

If not, then it is with your power supply. It might not be able to handle everything. This would explain why it improves when you added the second power supply.
Title: Re: How do I prevent video interference caused by electric motors
Post by: David82 on Jan 07, 2013, 04:35 pm
The same results are seen when using 8AA batteries instead of the power supply. Even connecting an uncharged capacitor will cause the video to momentarily flicker.
Title: Re: How do I prevent video interference caused by electric motors
Post by: PeterH on Jan 07, 2013, 05:44 pm

Even connecting an uncharged capacitor will cause the video to momentarily flicker.


I can't imagine why you would be surprised at this, given that the capacitor has very low series resistance and would suck a relatively large current from the power rail while it charges.

If you want a small power supply to behave (transiently) like a much larger one then the only way I can see to do it is to use some sort of accumulator. For example, you could use a big capacitor which is fed via a series resistor so that it charges relatively slowly, but can discharge quickly into the load. If the capacitor is too small (relative to the load) then the supply to the the load will 'brown out' but will not be able to drag the shared supply down with it.
Title: Re: How do I prevent video interference caused by electric motors
Post by: David82 on Jan 07, 2013, 06:39 pm
the power supply isn't the problem from what my experiments have shown. Even when using batteries, the same action still causes the camera brown-out.
Title: Re: How do I prevent video interference caused by electric motors
Post by: PeterH on Jan 07, 2013, 06:52 pm

the power supply isn't the problem from what my experiments have shown. Even when using batteries, the same action still causes the camera brown-out.


A brown-out indicates that the power supply (and regulator, and the circuit connecting all this to the load) isn't capable of supporting the load being placed on it. The fact that you see similar symptoms when running on batteries doesn't exonerate the power supply, it just means that you get the same problem running on batteries.
Title: Re: How do I prevent video interference caused by electric motors
Post by: HazardsMind on Jan 07, 2013, 06:59 pm
Quote
the power supply isn't the problem from what my experiments have shown. Even when using batteries, the same action still causes the camera brown-out.

Because you are not supplying enough current! The problem is you dont know what everything is rated, (what needs what)
The LCD could run on 12V @ 5A, the camera could be running at 12V @ 3A, and the motor could require another 0.5A. (spitballing numbers)

Your power supply can ONLY produce 12V @ 7.5A, whereas your componets may need 8 - 8.5A.
It worked correctly last time when you had 2 power supplies because you split the current. Your single power supply can not handle everything.

You need to find out EXACTLY what each part needs to opperate properly, then you get the power supply to run it all.

Not the other way around, unless you get all new low power components.
Title: Re: How do I prevent video interference caused by electric motors
Post by: dc42 on Jan 07, 2013, 08:04 pm
Connecting a large capacitor across the output of a power supply will cause a brownout on any power supply. Connecting a heavy resistive or resistive/inductive load will not, if the power supply is adequate.
Title: Re: How do I prevent video interference caused by electric motors
Post by: oric_dan on Jan 07, 2013, 08:46 pm
Quote
A brown-out indicates that the power supply (and regulator, and the circuit connecting all this to the load) isn't capable of supporting the load being placed on it.

This is not necessarily so, as already indicated several times. If the power leads are long and
have too much inductance, then you get large swings in voltage - at the load - with switched
load currents. That's what the info about the "Main Capacitor" was talking about.

Many good power supplies deal with this problem by running sense wires from the P/S straight
over to the load, so they can measure the voltage fluctuations and compensate. Negative
feedback stabilization.

Title: Re: How do I prevent video interference caused by electric motors
Post by: HazardsMind on Jan 07, 2013, 09:44 pm
@oric_dan(333)

Yea but that doesn't explain why the normal batteries have the same problem. I understand the use of the Main capacitor, to get rid of any voltage spikes or dips. But if the power supply doesn't have enough current to supply to everything as it is, then the capacitor won't have enough charge to do its job.

Now if he had access to an adjustable voltage supply, then he could rule out the power supply he is currently using. All he has to do is set the voltage to 12 volts and adjust the current, and keep monitoring it until he gets no brown outs or interference. Then get a proper power supply based on what he measured.
Title: Re: How do I prevent video interference caused by electric motors
Post by: oric_dan on Jan 07, 2013, 10:10 pm
Quote
Yea but that doesn't explain why the normal batteries have the same problem. I understand the use of the Main capacitor, to get rid of any voltage spikes or dips. But if the power supply doesn't have enough current to supply to everything as it is, then the capacitor won't have enough charge to do its job.

Yeah, if the power supply can't supply enough current, that's certainly needs to be fixed.
I thought OP was using a huge old PC supply.

Also, the business with the Main Capacitor is an illustrative point. It works best *IF* your
controller is competently designed, and then helps deal with the battery leads, which may
be longish for any #of reasons. OTOH, if everything in the ckt has long leads with nontrivial
inductance, then the cap probably won't do much.

Good design is a systems-level solution. Would be interesting to know how auto manufacturers
deal specifically with the brownout problem when the starter motor cranks. I imagine there's
a lot of brownout protection cktry inside the computer box.

Title: Re: How do I prevent video interference caused by electric motors
Post by: HazardsMind on Jan 07, 2013, 10:20 pm
Quote
Yeah, if the power supply can't supply enough current, that's certainly needs to be fixed.
I thought OP was using a huge old PC supply.


No its like a laptop supply

Quote
I imagine there's a lot of brownout protection cktry inside the computer box.


Im sure, but will they share it with us, probably not.
Title: Re: How do I prevent video interference caused by electric motors
Post by: David82 on Jan 07, 2013, 10:52 pm

Quote
the power supply isn't the problem from what my experiments have shown. Even when using batteries, the same action still causes the camera brown-out.

Because you are not supplying enough current! The problem is you dont know what everything is rated, (what needs what)


The LCD is small. It's only about 1A.
The camera is only about 1A.
I don't know what the cap draws when it is added.
The power supply is 90W/12V=7.5A
Batteries on the other had can output a heck of a lot of amperage but the problem still persists.

This is a better image of the test system:
(http://i.imgur.com/lnBxa.png)
It was suggested by Magician in another thread to put a inductor in series on the positive lead going to the camera. That makes sense to me as it would help smooth out current fluctuations caused by the sudden added load. What Henry value should I look for though?
Title: Re: How do I prevent video interference caused by electric motors
Post by: oric_dan on Jan 07, 2013, 11:53 pm
BTW, I found these pretty pictures showing a lot of fun designs,

http://www.google.com/search?q=star+grounding&hl=en&tbo=u&tbm=isch&source=univ&biw=990&bih=824&sei=4k_rUOvZFaaZiQK1koGYBQ
Title: Re: How do I prevent video interference caused by electric motors
Post by: PeterH on Jan 08, 2013, 12:09 am

Batteries on the other had can output a heck of a lot of amperage but the problem still persists.


I don't know what type of battery you're using, but if you're talking about conventional AA sized cells they're going to struggle to provide a couple of Amps never mind having anything in reserve for spikes in the demand.
Title: Re: How do I prevent video interference caused by electric motors
Post by: zoomkat on Jan 08, 2013, 12:33 am

Quote
the power supply isn't the problem from what my experiments have shown. Even when using batteries, the same action still causes the camera brown-out.


Your power supply can ONLY produce 12V @ 7.5A, whereas your componets may need 8 - 8.5A.
It worked correctly last time when you had 2 power supplies because you split the current. Your single power supply can not handle everything.


His powersupply may only produce .75a at 12v, who knows. Go back to the below and check that it is a "dual" supply. 

http://arduino.cc/forum/index.php/topic,140951.msg1059054.html#msg1059054
Title: Re: How do I prevent video interference caused by electric motors
Post by: HazardsMind on Jan 08, 2013, 12:47 am
Ok then, I tap out.
Title: Re: How do I prevent video interference caused by electric motors
Post by: pdwyer on Jan 08, 2013, 02:41 am
You will need to use shielded cable from the motor drive ICs (or board) to the motors.  Ground the shield in the cable to ground on your board.  Leave the shield open on the motor end.  Also, from looking at you diagram, you may need to clean up the wiring mess and/or use shielded cable in other places.  Try shielding the motor cable first, and let me know.

Patrick
Title: Re: How do I prevent video interference caused by electric motors
Post by: David82 on Jan 11, 2013, 09:04 pm
I did some tests. I need help interpreting the results.

measuring equipment: Fluke 287 history graph feature.

Theory: 90W PC power supply isn't good enough because it can't supply enough current when needed
Test: use car battery
Result: same video flickering problem

Theory: a drop in voltage when a load is applied is what causes the camera to flicker
Test: apply 4700uF 35v cap to circuit (which will also cause the video to flicker) and read voltage data from DMM.
Result: voltage only momentarily dropped from 12.1v to 11.8v
Conclusion: voltage drop is not significant enough be the cause of the problem.

what else should I test?
Title: Re: How do I prevent video interference caused by electric motors
Post by: zoomkat on Jan 11, 2013, 09:24 pm
Quote
what else should I test?


You need to observe the minimum voltage drop point with an o-scope instead of a DMM. Most DMMs cannot accurately show rapid voltage changes due to their design.
Title: Re: How do I prevent video interference caused by electric motors
Post by: David82 on Jan 11, 2013, 09:40 pm
but an o-scope only shows instant voltage fluctuations. It would be gone, off of the screen before I could get a chance to look at it..
Title: Re: How do I prevent video interference caused by electric motors
Post by: zoomkat on Jan 11, 2013, 10:55 pm

but an o-scope only shows instant voltage fluctuations. It would be gone, off of the screen before I could get a chance to look at it..


I would think an o-scope would have a trigger/hold feature for rapid events. Perhaps you should take your project to an electronics shop for a professional opinion. Nobody here knows the construction methods (soldered or twisted wires, wiring size, etc.) you used. If the cam requires a regulated 12v power source, any drop below 12v may cause issues.  No amount of whining, fantasy thinking, praying, etc will change the way your project behaves. If you have an arduino, you might be able to make a data logger setup to detect/record how low the voltage drops.
Title: Re: How do I prevent video interference caused by electric motors
Post by: David82 on Jan 11, 2013, 11:39 pm
my fluke 287 records a graphical display of whatever it is measuring. I don't know if an o-scope has that feature.
(http://1.bp.blogspot.com/_ld4qZws9ApM/Sl__J52kmCI/AAAAAAAAABg/PjuLoEPN5ng/s320/289.jpg)


I have a new experiment to try. I need some component that only allows amperage to be drawn gradually as if you were turning the knob of a variable pot. what would that be called?
Title: Re: How do I prevent video interference caused by electric motors
Post by: zoomkat on Jan 12, 2013, 12:18 am
Your fluke should have some features to allow you to see how low the voltage drops either ysing the max/min capture (100ms resolution) or duty cycle (which may have the shortest measurement interval).

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&frm=1&source=web&cd=1&cad=rja&ved=0CEMQFjAA&url=http%3A%2F%2Fwww.myflukestore.com%2Fcrm_uploads%2F287_289_umeng0100.pdf&ei=65XwUP28B-Ww0AHvyIGIBQ&usg=AFQjCNFvxUdKELcescSQ-fr3XYfgVGD0Uw&bvm=bv.1357700187,d.dmQ

Quote

Capturing Minimum and Maximum
Values
The MIN MAX Record mode captures minimum, average, and
maximum input values. When the input goes below the recorded
minimum value or above the recorded maximum value, the Meter
beeps and records the new value. The Meter stores the elapsed
time since the recording session was started at the same time.
The MIN MAX mode also calculates an average of all readings
taken since the MIN MAX mode was activated.
This mode is for capturing intermittent readings, recording
minimum and maximum readings unattended, or recording
readings while equipment operation precludes watching the
Meter. The MIN MAX mode is best for recording power supply
surges, inrush currents, and finding intermittent failures.
Response time is the length of time an input must stay at a new
value to be captured as a possible new minimum or maximum
value. The Meter has a 100 millisecond MIN MAX response time.
For example, a surge lasting 100 milliseconds would be captured
but one lasting only 50 milliseconds may not be captured at its
actual peak value. See the MIN MAX specification for more
information.

To activate the MIN MAX mode, press M. As shown in
Figure 6, the Meter displays e at the top of the
measurement page, and the MIN MAX start date and time along
the bottom of the page. In addition, the recorded maximum,
average, and minimum values appear in the secondary display
with their respective elapsed times.
Restart
119.81VAC
Stop
Start : 06/07/07 7:00 pm
Maximum 127.09
119.50
110.23
Average
Minimum
Auto Range
VAC 500 VAC
VAC
00:03:17
01:10:09
00:59:59
VAC
8:10pm 06/07/07
Min Max
est42.eps
Figure 6. MIN MAX Record Display
To stop a MIN MAX recording session, press M or the softkey
labeled Stop. The summary information in the display freezes,
and the softkeys change function to allow saving the collected
data. Pressing M again or the softkey labeled Close exits the
MIN MAX record session without saving the collected data.

Measuring Duty cycle
Duty cycle (or duty factor) is the percentage of time a signal is
above or below a trigger level during one cycle, as shown in
Figure 25.
The duty-cycle mode is optimized for measuring the on or off
time of logic and switching signals. Systems such as electronic
fuel injection systems and switching power supplies are
controlled by pulses of varying width, which can be checked by
measuring duty cycle.

Title: Re: How do I prevent video interference caused by electric motors
Post by: David82 on Jan 12, 2013, 12:24 am

Your fluke should have some features to allow you to see how low the voltage drops either ysing the max/min capture (100ms resolution) or duty cycle (which may have the shortest measurement interval).


It does but why would use that instead of the historical graph? Does the min/max have a much faster cycling time or something?
Title: Re: How do I prevent video interference caused by electric motors
Post by: zoomkat on Jan 12, 2013, 12:50 am


Your fluke should have some features to allow you to see how low the voltage drops either ysing the max/min capture (100ms resolution) or duty cycle (which may have the shortest measurement interval).


It does but why would use that instead of the historical graph? Does the min/max have a much faster cycling time or something?


I don't have your fluke, so I can't do actual test like you should be doing. The bar graph apparently updates 30 times a second, but I assume you will have to be able to visually determine the low voltage value during a very short interval. Where in your circuit have you measured using the bar graph method and what were the results?  I would think the duty cycle might be interrupt driven able to capture the shortest interval (the voltage trigger level would have to incremently lowered for each test to find the lowest value).