I've purchased this kit:
https://www.adafruit.com/product/1687
I've been using this as a reference:
http://www.ti.com/lit/ds/symlink/sn754410.pdf
I'm trying to power a DC motor from the kit and am having some issues.
I've connected ~5v input to vcc2 and 5v to vcc1 (as instructed – vcc1 connects to en 1/2 and en 3/4).
When I measure the voltage between either of these two and the ground, I get 4.8v (close enough to 5?)
When I then measure the voltage between 1a/ground or 4a/ground (the input pins) I get a voltage of ~0.66v. If I measure the voltage between 2a/ground or 3a/ground I get ~1v. If I disconnect vcc1 (and as such en 1/2 and 3/4) the voltage drops on these.
My issue is this, since 2a/3a voltage is above the max for low input, the 2y/3y pin is always set to high.
I'm struggling to understand this a little – have I screwed up something, or is this functioning correctly? I had to assemble the kit myself, I've double checked all the soldering, and as far as I can tell nothing is wrong.
Best Answer
If I'm correct, you've assembled the board and connected power, but have not connected the board to a controller, and the inputs are not connected to anything, right?
Under these circumstances, this circuit topology will in fact, treat these unconnected inputs as high. Simply ground all your inputs (except the enables, which you have correctly tied to +5). You should see all outputs go to 0 volts (or maybe a few tenths of a volt).