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This my first electronics project and it is based on this project.

I'm using a TI SN754410NE H-Bridge to control 2 small dc motors. I'm using an Arduino UNO for the control signals (USB powered) and a 6 V battery supply to power the motors. The battery supply negative is connected to Arduino GND.

It is actually working but there is something a bit unusual. When I measure the voltages being supplied to the 2 motors I get voltages for one motor of +/-4 V but for the second motor it is 3 V in one direction and -4 V in the other. I have checked all the connections and they are fine. Also, is it to be expected to get a significant voltage drop when using this type of device (h-bridge) ? I was naively expecting to get 6 V.

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Yes, this kind of voltage drop is normal for this part. Look at the values for VOH and VOL on page 4 of the datasheet. The high-side switch has a typical drop of 1.1V @ 0.5A and the low-side switch has a typical drop of 1.0V.

As for why your two motors are different, perhaps one of them is binding a little bit in one direction, and drawing a bit more current that the other.

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  • \$\begingroup\$ Thanks Dave. I tried swapping the motors over, and unfortunately that is not the issue as the problem is always seen on outputs 1Y and 2Y regardless of which motor is connected. \$\endgroup\$
    – Funky Oordvork
    Commented Jan 13, 2013 at 20:48

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