Battery for stepper motors and controller

A board that I have developed, a project not yet published based on PSoC4 and L293D

If you are switching the l393, right before it.

Plese explain. You mean on the high power line or the controller power line ?

These are anyway already separated, (not very different to be honest). The controller 5Vcc positive is from the power reulatore while the high power line (motor supply) will go to another power regulator. Some detail should already be done but this is the proof of concept idea.

if you put the optoisolators before the inputs of the l393, you can have

four-wire isolation.  The logic supply would have its own ground and V+,

and you would have a MOT+ and a MOT-.  The motor would just seem like leds

to the controller.

On Tue, Jan 12, 2016 at 4:34 PM, balearicdynamics <messages@element14.com>

I see. As a matter of fact, the power section is controlled by the two half-bridge L293 and there is any physical connection with the logic part. This is that makes me a bit suspicious with this method. Mot + is just controlled by the darlington while the logic part has no connection at all with the motors. These are already two separate lines. Or I am wrong ? Frankly I have never seen a motor contorller with optoisolators just because this fact. also those in my CNC (wokring at 24V instead of 4.7) nor those in the 3D printer controlled by an AVR 1286.

Imagine ground not to be the magic thing we draw on schematics, but as a -bus of finite resistance.  Now you see that by sharing a ground, spikes on the one circuit can be impressed on the other.

That's clear. I should make a try.

Now a different question arises: why this is never applied to - just for example - all the 3D printers I saw that has a stepper motor controlling method very similar?

Hi Enrico,

If you're using low-power motors then you don't need to have opto-isolation. Even on higher power circuits, opto-isolation is an option (a good option), but there can be other ways too. Depends on how much ruggedness you want to fault conditions, but other ways can be rugged too. For example the Infineon motor control board uses an automotive part (with protection for some fault scenarios), and it is directly controlled by the Arduino (through 10k resistors for current limiting).

Shabaz, it is what I am writing by some comments. When I made the control board for the vending machines, I have used optoisolators, just because there was 3-5 A ower motors working at 24 V and the same serial interface needed optoisolation because was working with a strange 12V communication protocol. But in the case of general purpose controller driving 1-2A max stepper motors powered by 5Vcc (4.7 V to be precise) it sounds a bit senseless as the same L293 can provide sufficient peak isolation.

Enrico

It is a little more expensive to implement because now another supply is needed, it is more trouble, more space and more money.  The consumer market gets some rather poor circuits because the market is so cost-sensitive.  Optoisolators and similar circuits are fairly ubiquitous in medical electronics, for example, because the market is professional and not so hyper-reactive to cost.  These are interesting circuits.  I am not telling you to use them so much as to encourage you to read the highly-rewarding application notes about them, then decide for yourself.  They have products nowadays called 'logic optoisolators' that require a minimum of design effort to implement. Opto-isolators are a little less popular now because bandwidth and circuits they protect are a little more robust by nature now.  There are other forms of isolators that use acoustic or RF energy instead of light that are used in special cases.  Transformers can also be used in some cases to minimize the energetic transfer across a barrier.