I have a 3 axis machine with 3 nema17 and a homemade pcb with 3 A4988 drivers. The PCB also have the 12V input (for motor power) and 5V input (for A4988).
The 12V and 5V come from 2 separate power supplies.
GND are all connected each other and with the arduino GND.
The problem is that when i power everything on, motors start to randomly spin, sometimes with complete steps, sometimes with non complete steps. If I put only one A4988 on the PCB, I can control the linked motor, but when I add the second A4988, motors stars to have problems. The same with the third A4988.
It seems that there is electrical noise that "give" HIGH input to STEP in A4988.
Anyone got the same problem?
Insert a pull-down resistor 10kohm in the STEP pin could be a good idea?
Homemade PCB - perhaps layout problems? Do you use a ground-plane? Do you have adequate decoupling
on each chip and for the supply rails? Is the 5V derived from the motor supply?
I have 3 A4988s on a veroboard circuit and I have never had a problem like you describe. I have used the wiring arrangements shown on the Pololu A4988 webpage.
I don't have a 5v supply - that comes from my Uno's 5v pin.
MarkT:
Homemade PCB - perhaps layout problems? Do you use a ground-plane? Do you have adequate decoupling
on each chip and for the supply rails? Is the 5V derived from the motor supply?
I don't think there are layout problems, I've checked all connections several times. I don't use a ground-plane.
As decoupling I've used 3 capacitors (as in Pololu webpage) on each VMOT/GND pin of A4988.
12V and 5V are from 2 separate power supplies.
Robin2:
I have 3 A4988s on a veroboard circuit and I have never had a problem like you describe. I have used the wiring arrangements shown on the Pololu A4988 webpage.
I don't have a 5v supply - that comes from my Uno's 5v pin.
...R
I've used a matrix board and jumper cables for connections. I've tried with 5V from Arduino, but same problem.
Did you have the jumper between SLP and RST? And 5V to theese?
Then perhaps your 12V supply is inadequate? Have you set the trimmer pots on the A4988 boards correctly
and measured the peak current demand from one of them?