H bridge

Motor driver circuits that can run the motor in both directions are called H-Bridge. I really don't know where the name comes from. Any bridge can be drawn in the shape of letter H or it can be drawn as a bridge.

H bridge drawn as a conventional bridge

 

Anyone who been thumbling with car window motor control or similar two direction motor control knows that we need a two bit control.

UP  DOWN

0      0      nothing happens
0      1      goes down
1      0      goes up
1      1      nothing happens

We kind of waste one state in the two bit control but you just have to live with that.

An H bridge motor control IC is one of the very basic components used in home electronics like VCR's since forever. SN754410 is a 'modern' dual H bridge. PDF datasheet. It has two 1A bridges that can control a 4.5...36V power rail by 5V CMOS/TTL compatible logic input. Perfect for us.

Playing with the crab was not very surprising. It wastes 1.4 volts as two transistors in serial are expected to waste. A bias current of 20 mA was unexpected. Not so harmful but we don't need it. I assume the bias is for maximum speed that we don't need.

A 16-pin DIP package can handle 2 watts of power in 'normal' conditions. 2 watts / 1.4 volts / 2 motors = around 0.7 amperes each. It seems that we are in the ballpark.


Conclusion

We can use SN754410 as a driver. However it would be good to either

1. Drive one motor per one SN..blah..blah..
2. Add some small heat sinking