Power Functions Motor Interference

[dsjove]

This is a Power Functions question. I recently purchased a wireless camera (which is amazingly LEGO units in size!) to go on my Mindstorms remote controlled train. The Power Functions battery supplies enough voltage for the motor and camera running at the same time. The problem is the motor (although on separate Power Functions circuit) is causing visual interference in the signal. If the camera is running off its own battery, no interference.

I am not an electronics guy. How does one begin to alter a circuit to filter out the motor interference?

FYI, the camera...
http://www.amazon.com/Wireless-Color-Ca ... 81&sr=8-12

[timpattinson]

I think the best solution would be to include a small capacitor in the circuit powering the camera - it cuts noise by resisting changes in voltage, although allows rapid changes in current. The type of capacitor really depends on the nature of the noise and the operating voltage of the camera
-Tim

[mattallen37]

I agree about the capacitor, but I usually use at LEAST 2 caps on a noisy line, and often a back shunted transformer (if I don't need much current). A voltage regulator can also help. I am not sure the setup of yours, or what motor you are using, but you could try using a 10 uf and 470 uf capacitor.

[nxtreme]

Pololu sells a neat little board, named the "Step-up/Step-down voltage regulator". It differs from most "normal" V-regs in that you can give it any voltage and it will output any voltage. Well, within limits of course but it would suit your application. It would be powerful enough to power your camera (aprox. 150 mA, right?) and you could power it off of pretty much anything, your PF battery holder, two or more AAs, rechargeable or disposable, one or two LiPo cells or pretty much anything that will give you enough mA.

You'll probably need to add a 33 uF electrolytic capacitor as well to keep everything stable (read the app note at the bottom of the product page), but aside from that it should work fine. Oh, the board also includes a auto-cutoff feature which will turn off the V-reg if the voltage drops beneath a certain level. This can be useful when using rechargeable cells, especially LiPos as over-discharging them can lead to some rather nasty things happening...

I understand if this might all seem a bit too overwhelming but if you do decide to go ahead with this or something similar, we'd love to help .

[dsjove]

Yes. I am overwhelmed!

Here is the setup:

Battery: http://shop.lego.com/ByTheme/Product.aspx?p=8878&cn=87
IR Receiver: http://shop.lego.com/ByTheme/Product.aspx?p=8884&cn=87
Motor: http://shop.lego.com/product/?p=8866&La ... &ShipTo=US
Camera Lights: [url]Lights: http://shop.lego.com/ByTheme/Product.aspx?p=8870&cn=87[/url]

The motor is on its own PF circuit. The light and camera is on the other.
I sacrificed an old RCX electric cable to adapt the camera's 9V battery cable to something I can stick on the back of a PF extension cable.

More about the camera...
The camera expects 8V. We are giving it 7.2V, which seems to be good enough.
The AC/DC power adaptor pushes out 500mA.
The camera can run off a standard 9V (400mA to 600mA?).
It is the transmitter in the camera that demands the most.

What I am building...
I have an old Hogwarts train that I have retrofitted with the above electronics and train wheels. The camera, after being glued to a 1x2 brick with fixed axle whole, fits very well on the front. You wouldn't even notice the front is a camera. The PF battery recharge power is now fed through metal contacts glued to the train bumpers. So, when the train is instructed to go home, it will start recharging when "docked".

I recently purchased the IRLink, http://shop.lego.com/product/?p=MS1046& ... &ShipTo=US, to control it with the NXT. And using the RCX to NXT adaptor cables, I have a fully automated train track switch using an RCX motor and RCX light sensor. I am using NXC, integrated with XCode, to program it all. Fun stuff.

My electronics knowledge is small. "Back shunted transformer" is greek to me

[nxtreme]

Yes, my suggestion was a bit extravagant, sorry . I think that Tims idea will work great, include a aprox. 100 uF electrolytic cap and a .1 uF ceramic cap. If your using the old "Lego brick" connector, you'll have to watch out for reverse voltage which could fry something... This could be solved with two diodes. I have to go now but if you have any more questions, ask them .

[dsjove]

I am worried about dropping more voltage. How much voltage drop can I expect from these components? Would the Pololu voltage regulator be sufficient? I am all for plugging in already made circuit and turning a dial!

[nxtreme]

If you used Schottky diodes, the voltage drop probably wouldn't be more than one volt. However, if your using rechargeable batteries, that's probably still too much . I think that the Pololu V-reg would work just fine. You'd still need to add two capacitors, a 33 uF and a .1 uF, just to keep noise to a minimum but it should work fine. I would wire it directly into a PF cable, that way you wouldn't have to worry about reverse voltage. You could buy extra PF cables either from Shop@Home, LegoEdu, BrickLink or maybe even eBay. LegoEdu has some cool parts...

That's what I'd do but, I occasionally over-do projects... . If you do use the Pololu V-reg, make sure you don't accidentally apply more than 9 V to the camera by adding a dab of glue to the dial, just to make sure it doesn't get bumped.

[dsjove]

A voltage drop will be too much, I am already lower than specifications!

Would I add the 33 uF and .1 uF caps to the motor line?

I trust then the voltage regulator reduces any spikes or drains caused changes in the motor voltage?

Does the voltage regulator output enough mA's? I keep trying to find out the mA output of the battery box. My multi-meter just died.

[nxtreme]

And, that drop means less range .

The other thing you could do is wire it or a power jack directly into a PF cable, that way you only have to get it right the first time. If your not using the V-reg, it'd be best to put the .1 uF cap as close as possible to the camera, the closer the better. The 33-100 uF cap would go as close to the camera as possible as well, but with preference given to the .1 uF on closeness.

If your using the V-reg though, the 33 uF would go on the power input of the V-reg and the .1 uF as close as possible (again) to the camera. AFAIK this is so that the small spikes and dips are filtered out right next to the camera and if there is a voltage drop in the power provided to the V-reg, the 33 uF will power it through those "rough times". Remember, I'm in no way an expert, somebody with more knowledge will most likely prove me wrong .

Yes, the V-reg will reduce power spikes and fluctuations on the power line, if not completely eliminate them. That's what the caps are there for, to help smooth things out even more. The V-reg will provide enough mA, provided you provide it with at least 3 V. It isn't exactly a power efficient regulator, consuming about 240 mA while providing 150 mA for the camera while powering the V-reg with aprox. 8 V.
In comparison, the PF train motor uses around 150-300 mA, depending on the weight/# of cars pulled*. I hope this answers your questions, if you have more don't hesitate to ask them!