How do I prevent video interference caused by electric motors

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?

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.

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.

Try:

Noise.jpg|349x444

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.

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.

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?

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.

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.

zoomkat:

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.

Applying a charged capacitor to the circuit will also cause the same temporary interference. What does that mean?

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?

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

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.

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?

If you are not going to read the answers then I am not going to tell you again. Good night.

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."

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

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

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...

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.