Live sound engineering is facing its biggest change ever during the winter 2012...13. Transition from tubes to transistors or from analog to digital was just natural evolution.

The way we do live mixing will be totally different than a year ago. The sound system will be controlled with personal mobile gadgets.

Naturally it was Mackie who made affordable equipment available for iPad based live mixing. I am a one man R&D team. I try to develop simple DIY solutions with a vision similar to Greg's.

Monday, August 13, 2012

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

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