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[Reply #45 on:]

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.

Insanity: doing the same thing over and over again and expecting different results.
Albert Einstein

[Reply #46 on:]

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

[Reply #47 on:]

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.

[Reply #48 on:]

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.

[Reply #49 on:]

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.

[Reply #50 on:]

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.

[Reply #51 on:]

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.

[Reply #52 on:]

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.

[Reply #53 on:]

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.

[Reply #54 on:]

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.

[Reply #55 on:]

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.

[Reply #56 on:]

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.

[Reply #57 on:]

@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.

[Reply #58 on:]

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.

[Reply #59 on:]

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

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.