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Author Topic: How do I prevent video interference caused by electric motors  (Read 5974 times)
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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."
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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


« Last Edit: January 05, 2013, 04:54:26 pm by HazardsMind » Logged

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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

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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...
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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.
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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 smiley-sad

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.
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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...)


* ckt1.png (61.42 KB, 1185x439 - viewed 23 times.)

* ckt2.png (60.53 KB, 1185x439 - viewed 22 times.)
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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.
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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.
« Last Edit: January 05, 2013, 06:30:25 pm by HazardsMind » Logged

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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.
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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.
« Last Edit: January 05, 2013, 06:55:58 pm by David82 » Logged

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