petrAgain wrote:Yes, you need two power supplies.
OR one 10v power supply and a voltage converter, 10 to 5v. These can be simple and cheap (29p) but, for the power to drive a pi, they get rather hot as we found out when the heat sink started to melt the lego it was touching. We now use a switching voltage adapter (5 pounds) to deliver half an amp at 5v to the rpi, and let the 10v battery deliver 2 amps via a driver board to some motors. The size of the motors is limited to the maximum _amperage_ the darlington(s) can handle.
The _only_ thing that should connect the pi to your driver board should be 5 volt / 0.01 amp signal wires... and the ground wire.
Hope that helps.
Interesting, I appreciate both pieces of advice, however it appears that you guys each gave different advice: either I need two separate power adapters (one feeding the terminal input of the board [the power from the pi only powers the board this is true] and the other feeding the signal coming out of the Darlington), or only one single power adapter from the signal coming out of the Darlington and nothing directly connected to the relay terminal on the breakout board?Burngate wrote:I may be misunderstanding it, but as far as I can see:
On the Adafruit PCA9685 board, the main chip is powered by the 3v3 from the Pi, as in your top picture.
The V+ on the power terminal-block only supplies power to the middle V+ pins of the three-pin servo output blocks. Since you're not using those, you don't need to connect power to the terminal block.
The PWM outputs feed the bases of the darlingtons, the collectors feed the servos, and your 12v supply feeds those.
The 12v doesn't need to go anywhere else (though you may need to connect it to pin 10 of the ULN2803 if you wish to make use of its in-built diodes)
Ground, of course, must be continuous between the Pi, the PCA9685, the ULN2803, the negative of the 12v supply, and the servos.
I appreciate the advice! In fact, I did this superficially prior to my previous reply, it seems that petrAgain has more direct relevant experience in that he runs a similar setup but he has only a couple total posts, whereas Burngate has thousands of posts and has provided a lot of great advice. It's definitely possible they both are right for different setups, although of course I was looking for the "best" answer being the most stable and cheapest. Before trying anything I want to do as much research as possible - I'll venture forward if needed, but if anyone else can chime in with any more insight it would be awesome? Thanks again!davidcoton wrote:Both posters are answering from their experience and the setups they have used. You need to determine which is applicable to your situation, and the experience of each poster.
1) Look at the post count, and possibly review some of the posters' other posts -- are they clear, unambiguopus, and generally accepted as correct by others? (But note post count is not definitive -- some people can post a lot of rubbish. To avoid paranoia, I don't have anyone in particular in mind.)
2) Judge whether the post details are corect and fit your situation. For example, what voltage are the Pi GPIO siganls to the Darlington? If you don't know, find out before you get something wrong and destroy your Pi. Knowing the correct answer will show who has posted with more attention to getting the details correct.
Yes!! Good catch on the pin, it was just an error in the drawing. I forgot about the ground to the Darlington, so big thanks on that!Burngate wrote:Actually ... No!
Your new drawing shows a 16-pin 2003; your original was a 18-pin 2803. That's of no consequence - the 2803 merely has an extra Darlington.
However, this new drawing shows your inputs going to Darlingtons 5 & 6, but the outputs coming from Darlingtons 5 & 7.
I assume this is just an error in the drawing, and you will connect it correctly, whichever Darlingtons you decide to use.
However, there is one connection you've left out, and without it it won't work! That's the ground connection to pin 8 of the 2003 or pin 9 of the 2803.
It's there in the second drawing in your first post. Is this also merely an error in your new drawing?
So, with those corrections, it will work!
As regards number of power supplies: yes, you only need one, unless you also count the one supplying your Pi, in which case you need two.
petrAgain was counting the 5v one supplying the Pi, and is correct in what he says. You need the Pi's 5v and the Servos' 12v.
I didn't actually specify a number. I understood you to be asking if another supply - so a second or third, depending how you count them - was needed to connect to the screw-terminals or to the V+ pin on the edge. You don't need that, so, as in your drawing, you only need the servos' 10v supply as well as the Pi's 5v.