I have an L293 motor driver chip, in which the two input pins are used in order to turn the motor forward or reverse, or stop it. So I wοnder if I could use only one input pin, ...

For running mode: Since Input1 should be the opposite of Input2, why not sending a signal from Input1 to Input2 via a hex inverter?

For stop mode: why not just sending analogWtite(Enable, 0) to Enable pin?

That way I could save an extra Output pin from Arduino. Do I lack some important detail?

My question goes the same for all the L29x family.


1 Answer 1


A H-Bridge has 3 modes of operation in addition to disabled. The ENable pin, when driven low, disconnects the power and stops the motor from being actively driven it is true. However that is not the same as the STOP mode of the H-Bridge.

The logical internal connections in the H-Bridge for the three modes are like this:

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When in STOP mode the motor is effectively short circuited and the power supply is disconnected. When the motor is spinning and not being actively driven it is generating power. By feeding that power into a load you increase the load on the motor itself, slowing it down. The bigger the electrical load the slower the motor will go - and you can't get bigger than a dead short. So this mode effectively stops the motor in its tracks. It puts the breaks on.

Conversely, if you just disconnect the power, there is nothing much to stop the motor spinning, so it will keep going depending on the amount of friction, wind resistance, inertia, momentum, etc.

If you are happy with that kind of operation then yes, your method will work fine, since you will have access to forward, reverse, and a way of controlling the power to the motor. You just won't be able to apply the brakes, and you will have to either rely on the natural slow-down of whatever you are driving, or do something clever involving using just enough reverse to stop the motor before cutting the power.

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