Electrical Engineering Stack Exchange is a question and answer site for electronics and electrical engineering professionals, students, and enthusiasts. It only takes a minute to sign up.
Sign up to join this community
I need to build a programmable current source from a 8051 microcontroller.
It needs an output current from 0 to 10mA maximun.
How do i go about doing this? what circuits do i need to build?
I was going to do a 20 steps - with 0.5mA so from 0 to 10mA is 20 steps.
Here's an example that goes from -15V to +15V with +/- 18mA, so unless you need higher or lower voltages it should do the trick with two chips and a handful of passives. It provides a great deal of resolution and stability, and requires positive and negative supplies, so it may be overkill.
If you let us know what voltage range you're looking for, though, a simpler circuit may better fit the bill.
Here's another option, 100mA and 9V: http://www.discovercircuits.com/DJ-Circuits/100ma-current-source.htm 1 chip, two fets, and a handful of components.
One cheap solution is to create a PWM signal, filter it with a RC cell, and then feed it to a voltage-to-current converter. In the simplest case, this can be a transistor with a resistor in the emitter, and the load in the collector. But you can also use an op amp for this. Since you only need a 20-step scale, this may be enough for you.
A better but more expensive solution is to connect a DAC to 5 of your digital outputs, and feed the output of the DAC to a voltage-to-current converter as before. I think there are even some DACs which directly control their output current. Since you only need 5-bit resolution, you can even build a R-2R DAC yourself, as described here.
In the end, the optimal solution depends on your project's constraints (time? price? size?).
