Greetings to everyone.
This is my first post in this important forum for makers, and I’m a maker!
I have to drive with a PIC many stepper motors, and to do that I would use this multiplexer
http://www.theremino.com/hardware/adapters#multiplexer
for multiplex DIR and STEP, but as I have to manage one motor at a time, I would disable all unused motors in order to reduce the overall current and enable only the addressed motor self activating the ENABLE pin when STP change its state.
This approach is avoid to multiplexing the ENABLE line.
I’m thinking to activate the ENABLE pin using the STEP line, with a capacitor, resistor (used to discarge the capacitor) and a diode).
This is a completely crazy idea or you think that have some hope of being able to be used?
Leo
Hello, Leo.
I do not know how well it will work for your application, but I do not see anything obvious in the datasheet that would prevent it from working. Page 10 of the A4988 datasheet discusses how the enable pin functions on the driver:
Enable Input (ENABLE). This input turns on or off all of the FET outputs. When set to a logic high, the outputs are disabled. When set to a logic low, the internal control enables the outputs as required. The translator inputs STEP, DIR, and MSx, as well as the internal sequencing logic, all remain active, independent of the ENABLE input state.
The LOW->HIGH transition on the STEP pin causes the driver to change steps and the logic of the ENABLE pin is inverted from the STEP pin. So, if you have ENABLE tied to STEP, the board will be disabled after the transition, and it seems like the step will probably not occur until the two pins are LOW again.
The cogging on stepper motors (the notches you will feel if you rotate an unenergized stepper motor by hand) occurs in full steps, so microstepping will probably not work very well. You should also be aware that the torque of this cogging is very low, so your motor will not hold position very well or the shaft might not stop spinning immediately when the driver is disabled.
It is not clear how you plan to use the resistor, capacitor, and diode in the circuit to connect ENABLE to STEP. It should be possible to tie the two pins together without any additional components.
If you decide to experiment with this, let us know how well it works.
-Nathan
