Success!

02/15/2011

Success indeed!  I controlled a DC motor through an Arduino UNO and a SN754410 h-bridge chip.  I can’t say I totally understand what my problems were before.  I think what happened is that I didn’t have a common ground for the Arduino, SN754410, and the motor power supply.  At one point, I measured 32V between the ground for the motor power supply and the Arduino!  That voltage went away when I plugged my power supply into the power strip as my computer connected to the Arduino – at that point I felt safe to connect all the grounds together.  I also neglected to connect 5V power (pin 16) to the SN754410 at first.

I used a 12V lead from an ATX computer power supply for the motor supply (SN754410 pin 8) and the Arduino 5V output for SN754410 pin 16.  With the enable pin (pin 1) of the SN754410 at 5V, the output (across pins 3 and 6) was about 10.5V, I think.  I put some resistors (like 2 ohms) between the motor and the SN754410 to try to protect from voltage spikes induced in the motor (back EMF?).  I didn’t want to have a voltage drop of more than a couple of volts or the motors might not turn much.  Anyway, it worked great!  I got a screaming motor that tried to run off the table instead of a near-ultrasonic whining and a slight twitch.

This is really exciting.  Not only can I now make a robot that the Arduino can control, I’m sure I can control the SN754410 (motors!) with a simpler/cheaper circuit with digital output!  I think the output from the suspended bicore circuit may be just right for connection to the direction pins (2 and 7) of the SN754410.  A small, solar cell could charge a capacitor with a circuit to energize the enable pin (pin 1) of the SN754410 when it’s ready to power the motors.  Then we’ll have short bursts of solar-powered sun tracking!  I honestly don’t even fully understand what the suspended bicore is, but it looks like an easy way to get a digital signal telling my circuit which direction to turn toward the sun.

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