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H-Bridge L293D voltage bleedthrough

Other Parts Discussed in Thread: L293D

I'm working on a Bluetooth project which requires a motor to turn something. I had to purchase the H-Bridge L293D for reverse rotation capability of the motor.

It does work however, it has a 1.1volt bleed through on the non active logic pin. I've tested the leads from the micro controller Arduino without being connected to the H-Bridge. The none active lead shows 0 volts while the other active lead shows anywhere between 4.7 to 5.1vdc. Which is fine. However, once the leads are connected to the H-Bridge L293D the output leads should show same voltage. But they do not. The active lead reads anywhere between 3.8 and 4.1vdc sometimes up to 4.7vdc but not all the time. And the none active lead on the H-Bridge which should have 0vdc shows 1.1vdc. And the other way around as well. So anytime a lead connected to an output pin of the H-Bridge made not active by micro controller is not supposed to have voltage, right? But those leads show 1.1vdc.

Is the motor connected feeding an EMF back into the H-Bridge? The motor is a 5volt 500ma gear motor. The voltage to motor is 5vdc. The vdc to micro controller is also 5vdc, The vdc to H-Bridge is also 5vdc coming from the micro controller.

My question is why does an inactive output pin on the H-Bridge show 1.1volts? Can I get help/answers please.



  • Hi Nic,

    Our expert has been notified and should respond soon. While waiting can you provide some additional information?
    Can you clarify the leads (active, non-active, output) by using pin numbers?
    Are any of the logic inputs floating?
    Can you provide a schematic also?
  • Hi Rick, I'm not quite sure what floating means? Active means that on my android phone I pressed a button to turn on a pin on the arduino. Which is now active and sending voltage to the H-Bridge. Let's say this pin is number 2 on the H-Bridge. The other pin on the H-Bridge is logic pin 7 which should at that point not have any voltage on it. The problem is that it does get 1.1vdc. I'm just not sure if that's normal or if something is wrong with the H-Bridge?
  • Hello Nic,

    To clarify, are you saying that you are measuring the voltage on Pin 7 and you are getting 1.1V when you are expecting 0V.

    If so, Pin 7 is an input pin to the device, so anytime there is an input pin to the device it should not be left floating. Floating meaning that it is not connected to anything. Is this pin not connected?

    If an input pin is left disconnected, then there is always a possibility for the voltage to be in an unknown state. Pin 7 should be forced to a known voltage state so that it doesn't "float".