# Circuit design for DC motor control

I 'm planning to control a DC motor via certain signals. Motor requires 9 V, 700 mA of voltage approximately. The voltage will be provided by a Ni-Cd battery. However, the signals that are responsible for the control of the motor are the output of a BeagleBoard-xM (1.8 V, 20 mA approximately).

How can I combine the signals with the battery voltage in the circuit I have to construct? I am a begginer in electrical engineering and any suggestion would be appreciated.

• Do you just want the motor to run or stop or are you wanting to be able to reverse the motor's direction. Maybe you are also looking for speed control. It may surprise you but these answers may help the answer shorter and more accessible to a beginner. It will probably help if you provided a link to the motor's data sheet. – Andy aka Nov 1 '13 at 23:14
• I would like to run/stop the motor and reverse it's direction. For the moment, I don't have access to the motor, I just looking for the idea for combining low-voltage signals with high-voltage DC motors. – dempap Nov 1 '13 at 23:26

The simplest form of motor control is on or off: -

This uses a BC547 transistor fed via a 10k ohm resistor and will accept logic levles as low as 1V. The BC547 then turns on or off a p channel MOSFET capable of supplying decent current to the motor.

Ignore the 12V - this circuit will work at 5V or well over 50V with one slight modification. I won't add anything more in case you are looking for something more sophisticated like PWM control or H-bridge reversing.

H-bridge motor reversing: -

This looks like a good chip for the motor you are planning on using. Note that it has two supplies - one for the motor H bridge (this can be 1.8V up to 11V) and a totally seperate supply for the logic and you'll need to connect this to 1.8V for your logic IO to work properly.

• After a measurement I made, the signals are 0.44 V, 4.5 mA approximately. I 'm sending 2 signals (one for forward movement and the other for backward, while no signal means no movement). I think an H-bridge is able to control these signals. However, I 'm planning to construct the circuit on a breadboard and I noticed that DRV8837 refers to microelectronics. This is a problem, isn't it? – dempap Nov 2 '13 at 15:36
• I'd be worried if the signals are less than a volt. Are you sure you measured correctly and how did you measure the current? There are other H bridges that will probably be easier to breadboard, have you tried googling cos that's what I did . – Andy aka Nov 2 '13 at 15:49
• I measured once again the output via a polymeter when a signal is sending (both voltage and current) and is the same as I reffered. I 'll make my research for an H-bridge. I just wanted to ensure that an H-bridge is the appropriate component for my design. – dempap Nov 2 '13 at 16:38
• if your logic supply is 1.8 volt then you're output is going to be either the same or 0v. Are you sure you weren't measuring an IO line that's toggling faster than your meter can detect? Was it possibly an AC measurement you took? If an ac measurement registers anything above 10mV the the line is likely to be toggling at a high rate which your meter averages when measuring dc. Please don't measure the current, you could damage the device. – Andy aka Nov 2 '13 at 17:35
• You are definetely right, as I 'm measuring an I/O line that's toggling. In this case, voltage is 1.8 V or the value that multimeter indicates? – dempap Nov 10 '13 at 19:55