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I built the circuit from this page and it works just fine but what I don't understand is what the EN pins are for. It says right on his diagram of the pins that you need to connect it to power to run the motors but I forgot to connect it and it works just fine. from what I understand reading the datasheet and that link my motor shouldn't be working at all.

Thanks

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  • \$\begingroup\$ You need to read the data sheet for the H-bridge chip. All the pin functions will be described there. \$\endgroup\$ Apr 1, 2013 at 19:45

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The page you link to has a function table that says it all:

enter image description here

When an enable input is LOW, the effect is that the motors will be stopped.

The SN754410 datasheet shows how the inputs of that chip are implemented:

enter image description here

This circuit has the property that an unconnected input is high (you must pull it low to make it low). Hence you can leave it unconnected if you don't want to use this input to make the motor brake.

NOTE: most modern chips do NOT have such inputs, and don't like it when their inputs are unconnected. It is good engineering practice to connect all inputs to a well-defined level.

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  • \$\begingroup\$ Sweet, that makes it clear. I also agree, I don't like "magic". I was confused though when I saw it working perfectly and then realized I had forgotten to connect a wire! \$\endgroup\$
    – Kenn
    Apr 1, 2013 at 20:12

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