I’m trying to use a Qik 2s9v1 controller to drive a Solarbotics GM13a motor. The controller will take serial commands from a computer using the RS232 adapter board.
I’d like to power it off of a wall-adapter. My initial plan is to use a 6V adapter to drive the motors, and use a 7805 regulator to feed a 5V logic channel.
But, of course, the Qik guide says that I need to keep the logic power and motor power separate, or at least “decouple the two by using large capacitors and/or a regulator.” What does this mean, exactly? Is my 7805 regulator sufficient? By ‘large capacitors’ does it just mean running the 0.1uF capacitors across the motor leads, or is there some additional capacitor magic that will help? Are those measures, combined with keeping my motor wires short and twisted, likely to be sufficient? How noisey are the Solarbotics motors?
Is there a smarter way to do this? Of course I could run two separate wall-adapters into the same box, but that seems kind of silly. I would rather not use batteries; the project is supposed to run constantly over a long period of time.
Those motors shouldn’t be too noisy, so you generally shouldn’t have much trouble. The 0.1uF caps across the motors are separate from capacitors on the power supply, for which 0.1uF is small; something like 100uF or more starts getting big, though you probably won’t need that here. By the way, I think the 7805 needs more than 1V dropout, (unless you’re using some modern version), so you might need something like a 7V or more on its input. Also, many wall adapters are not regulated, meaning an adapter labeled 6V might give you 10V or more with no load. So, you should measure the output with no load to see what your adapter does.
Hey Jan – Super-helpful advice, thanks for the fast reply!
Where should I put the <100uF capacitor(s)? Just in sequence between the power supply and the regulator? Or between the regulator and the Qik? Or somewhere else?
It sounds like I will want two voltage regulators – one for the logic and one for the motors. Does that sound right?
You should be able to get by with one regulator (for the logic). For the caps, I meant >100uF in the sense that you want big, and 100uF is when you start getting there. “In sequence” is not a good term to use here; if you meant in series, that would be wrong. As I said before, I don’t think you need them, so I’d start without them and only add them if I had trouble. Putting the capacitor on a power supply means connect the capacitor across, or in parallel with, the power line and ground. Most larger caps are polarized, so make sure you have the plus lead on the power pin and the minus lead on the ground pin.
A final question: is there a good way to measure the amount of noise on a line? It seems like there should be a better way to test solutions than just waiting to see whether the microcontroller freaks out. An oscilloscope?
