dc motor example > L293D VS L293E


i wanted to build the dc motor control circuit as described http://itp.nyu.edu/physcomp/Labs/DCMotorControl.

since i couldn’t get my hands on a L293D i ordered a L293E instead since they seemed to be pretty much the same, except for the additional sensing resistors. now i received the parts and built the circuit - and it doesnt work at all =/

while all connections etc seem to be just fine, the motor doesnt move. now i was wondering if someone could tell me what those sensing registers actually are? this way i could probably figure out where the problem is… the datasheet says:
“Additionally, the L293E has external connection of sensing resistors, for switchmode control.”
i’m really new to this, thus i don’t know what switchmode control means…

to test the circuit i simplified the code to

digitalWrite(motor1Pin, HIGH);  
digitalWrite(motor2Pin, LOW);

the strange thing is that when i apply the multimeter in voltage reading setting to the the specified INPUT pins and the L293s GND it prints the expected voltage (~9V and 0V), yet the OUTPUT pins on the L293E both read ~5v…
after i noticed this i took my power supplies GND and applied directly to the motor, which made it run. when i switch HIGH and LOW in the code, i have to apply the power supplies GND to the other power input on the motor, so this seems to be ok…

here is a picture:

your help is greatly appreciated…

best regards,

dear daniel,

thank you so much for your reply! i just got the example to run. indeed the power supply was too low on voltage, but i never figured out because i had my meter in a wrong setting that seems to double the reading! i’m now using an actual 9V battery and it works (with a different motor).

i also grounded the sensing pins like you pointed out. the only thing i don’t get is the thing you wrote about the protection diodes - could you be more specific on that? i checked the data sheet (http://docs-europe.electrocomponents.com/webdocs/0024/0900766b80024715.pdf) and can’t find them by myself…

again, thanks for your help, works great now!

best regards,