After I posted this question I kept fiddling and found the required connections. I will post the solution here so that if anyone else is looking to do something similar they won’t have to repeat the testing.
A brief overview of my setup:
1 x Arduino Uno running GRBL 0.9i
2 x Synthetos G-Shields
1 x Homemade CNC with dual Y-axis (2 motors driving the gantry)
My problem:
I did not want to buy a tinyg because of the following reasons
1. I already had the Arduino/G-shield setup
2. The price of a tinyg is 3x the price of G-shield
3. I did not want the possibility 4 separate motor signals, just a duplicate of one
4. I did not want to simply wire the motors in parallel because of the reduced power available and the extra strain on one driver
My solution:
Because the G-shield is just 3 DRV8811 being given directions by an Arduino Uno (ATmega328p) it seems that it should be possible to send the same signal from the Arduino to two G-shields and therefore power 2 motors with the same signal using a separate driver for each. (1 on each board)
The next step was simply to find what pins to connect from the original G-shield to the new one. I had a “dead” Arduino Uno so I removed the ATmega328p from the board and simply used this board to hold the second G-shield. I did not plug any power (USB/DC) into this second board. I simply jumped the 24V from the first board over to the second. I found that if you connect the following pins it is very straight-forward to achieve this.
1. IOREF
2. GND
3. Stepper Enable/Disable (D8)
4. Direction for axis (D5-D7 : X-Z)
5. Step Pulse for axis (D2-D4 : X-Z)
6. +/- 24V-30V Supply
The direction/step pulse pins only need to be connected for the axis desired.
As for the second question of my original post; I put on oscilloscope on the step pulse pin for the axis being used and measured the frequency as well as the voltage of the pulse train. I found that a brief 5V signal is sent at a frequency defined in the user settings.
Theoretical Frequency
Rate:500mm/min
Steps/mm:321.5
500mm/min*321.5steps/mm=160,750steps/min*1min/60sec=2679.17 steps/sec or Hz
Measured Frequency
2.677KHz
As you can see the frequency is able to be calculated. I plan to design a small circuit that will use a potentiometer to vary the frequency of the pulses, thereby circumventing the Arduino altogether and allowing the axis of your choice (the rotary axis in my case) to be rotated indefinitely with no commands or even communication from the computer. I will try to post the schematic here when I design the pulse circuit.
If you have read this far I hope you find this useful.
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