Troubleshooting a L293D Circuit

Hi all,

After two days of trying to hunt down the problem, I’m throwing in the towel and pleading for help =( …

I’m putting together a circuit which drives two motorized valves via a L293D (see attached). The two header ports at the top and bottom on the left hand side lead to the valves. The next one along at the bottom feeds 12v into the circuit. When I test it, though, the top valve works just fine - but I can’t get anything from the bottom one. I’ve chased round the circuit for continuity, and tried rebuilding it on a breadboard (where annoyingly, it works)…

Just to help me narrow down the problem - can anyone see an issue with the circuit itself? If not, I can assume I’ve done something wrong with the build…


Hi, can you post a copy of your circuit please, CAD or a picture of a hand drawn circuit in jpg, png or pdf. And post a copy of the sketch you are using to test the L293D.

Thanks, hope to help.

Tom..... :)

Have you cut traces on the stripboard in all the places you need to?

Hiya - have attached a (crappy) diagram of the circuit, hopefully it makes sense. The test code looks like this…

const int controlPin1 = 7;
const int controlPin2 = 8;

void setup() {

void loop() {
  digitalWrite(controlPin1, LOW);    //SWAP THESE TO REVERSE DIRECTION
  digitalWrite(controlPin2, HIGH);

Hmm, seems to be working now - I swapped the chip ... it must have been duff. :~

You perhaps fried it? Have you connected all the ground pins and added decoupling on both supplies near the chip?