How to do a good Stepper driver?

[MatheusLPS]

So people, I want to build a CNC machine from begining..

So I was searching info about the drivers that controls the stepper motors...

Most of the circuits I found uses the L297 and L298 IC.

In this moment I know that in CNC construction we use a voltade higher that the nominal voltage of the steppers and limit the current to the nominal value.

I understand how to use the L287 e L298 but I do not want to use them. I want to build my own driver with a PIC. The programing is not the problem.

The real problem is that I need to measure the current on every windings of the motores to limit it with a transistor and PWM...

But I can not measure, I do not know how. I thought of use a SHUNT resistor: a small resistor in series with the load and I read the drop voltage the terminals with PIC and calc the current. Then aply the right duty cicle. But imagine a 5 wire stepper. I will need 4 resistors, 1 for each winding and I have 3 motors. So 12 sense, shunt resistors, is too much!

Is there a way of measure this current? Is this a good ideia use a microcontroller to do the job? And not use the famous L297 and L298 pair?

bye

[JamesNewton]

You might like to check out the open source Linistepper design:
http://www.linistepper.com

Especially the "how it works" page and the schematic.

Consider sharing what you do? Thanks!

[kam]

So people, I want to build a CNC machine from begining..

James above has a complete solution for CNC, and people already have built one (find details in his site).