Motor Controller Design Help Needed

[darrenkarp]

Hi all,

I want to try and design a simple circuit using a PICAXE chip that will allow a 12vdc motor to be controlled. I want the chip to detect an excessive current draw from the motor (which would indicate it has hit something) and stop the motor. The circuit should also allow the motor to spin in either direction.

Can anyone advise a PICAXE chip that can detect current draw from a standard 12vdc motor with only a + and - wired connection?

Many thanks
Darren

 

[Andrew Cowan]

Hi Darren.

No PICAXE chip can detect current with a + and - connection. If you want to sense current draw, you will need a shunt resistor (small value resistor, eg 0.1 ohms. measure the voltage drop via ADC, calculate the current). The alternative method is using a hall effect sensor, although this is not great for small currents.

For driving the motor, I recommend a L239D (up to 1A), or an L298 (for up to 2A). These are H bridge drivers, so the motor can be reversed.

What's the application?

http://www.picaxeforum.co.uk/showthread.php?t=9909 was a recent thread that had lots about measuring motor current to see when the motor is overloaded.

Andrew

 

[goom]

Or try the LMD180200. Full H bridge (forward and reverse), 3A continuous current. It has a current sense pin which delivers 377 uA/A. Connect the pin to ground via, say, a 2K resistor. This will give 0.754 V/A which can be read by a Picaxe ADC input. It also has inbuilt thermal cutout protection, and a thermal flag output which goes low at 145°C, so can be input to the Pickaxe to detect impending overload.
Schematic, PCB layout and code for hobby RC receiver input available for the asking.

Kevin

 

[papaof2]

Did you mean LMD18200? There's a page about using it for model trains here:
http://home.cogeco.ca/~rpaisley4/HBridge.html{/URL] It's about $15US. Data sheet is here: [URL]http://www.national.com/ds/LM/LMD18200.pdf

JOhn