Using same GPIO pins to control multiple stepper drives

Question

I have an Arduino Mega 2560 and I want to control four 23-frame steppers same speed/direction for a conveyor application. I want these to be synchronized exactly as possible for smooth operation.

• Can four TB6600 drivers be daisy chained to the same Arduino GPIO pins?

• Is there a limit to how many number of drivers I can daisy chain?

• I'm wondering about current draw from the 5 volt Arduino GPIO, spread out over many drivers.

Thanks for your help!
Bob

• jsotola: daisy chain means connected in series, not connected in parallel ... irepo.primecp.com/2016/05/280836/…

Answer 1

Those devices use opto-isolated inputs. To all intents and purposes they look just like an LED with a resistor in series.

The built-in resistor looks like it sets the current to "between 8mA and 15mA" and typically 10mA, though it's impossible to say what it actually is. So we'll take the worst-case scenario of 15mA.

The Arduino has an absolute maximum of 40mA, and a recommended maximum of 25mA from each IO pin, with a maximum of 200mA in total through all pins.

That means you ideally can't really have more than one TB6600 per IO pin, but you could get away with 2 per pin, certainly no more.

To run lots in parallel you would need a separate set of drivers that can "fan out" the low-current signal to either a single high current signal or a parallel set of low-current signals.

It looks like you provide 5V to one pin of each input (the anode of the opto-isolator) and sink the current through the other pin (the cathode of the opto-isolator) to ground through your IO pins. That means you could use a single large N-channel MOSFET to sink all of the cathodes in parallel and invert your IO logic in software.

• Robert Born: So the MOSFET is acting like a relay keeping the IO signal intact (not too much draw on Arduino) while being able to sink the sum total of all tb6600 drivers involved?
• Majenko: @RobertBorn Correct, but also as an inverter, so a HIGH would turn on instead of a LOW as you would normally use for that device.
• Bob B: Please forgive me .. I'm more of a high power electrical guy. Actually I get into way too many kinds of projects :) In order to not have to mess with my control SW and elegant GUI I paid a college kid to build for me .. could I simply reverse the common to the tb6600 inputs from +5V to ground? I still need to study the connection of the MOSFET. Another thought .. I've used these opto-isolated signal boards before. But maybe they are not high speed enough to handle the PWM signal?
• Majenko: @BobB You could use two N-channel mosfets, one as an inverter (as in an RTL inverter) or maybe a P-channel MOSFET to switch the 5V signal, sure. Or add an actual inverter chip to the outputs (74HC00 gives 6 inverters in one chip). There's lots of things you could do.