I am trying to figure out how I can use an Arduino to run an MC-60 Motor Controller.
Lets backup a little and describe how I got here.
I own a Mikron 79 gear hob. It arrived without a motor. The manual lists three different motors that were shipped with the machine:
- 0.25hp 980 rpm
- 0.4hp 2,800 rpm
- 0.3/0.5hp 1,400/2,800rpm
Then the manual lists 7 different pulley sizes that can be put on the motor. So I am confused. I figure the best route is to find a variable speed motor and then figure it out later.
I looked at a 0.5hp 3 phase motor and VFD and realized I am looking at $100-$200 to set that up. I am too cheap for that.
Another option I have looked into in the past was a variable speed DC motor salvaged from a treadmill. Craigslist led me to a free treadmill with a 1.5hp motor, a MC-60 controller, and a PB-121 power supply.
Can I set up an Arduino to measure the speed of the motor (the treadmill came with a reed sensor and I have a hall effect sensor) and feed a signal to the MC-60 to have it maintain a desired speed?
I found may references to Arduino and MC-60 on the web, but none provided a definitive description on how to get them to work together. Just lots of questions and suggestions.
I did connect a potentiometer to the MC-60 and get the motor to spin up. Documentation leads me to believe that the MC-60 is designed to work with a 5k potentiometer. The signal is supposed to be 0-12 volts.
The obvious route is to use a digital potentiometer. I found some inexpensive digital pots that can work with 5 volts. The expensive digital pot that works with 12 volts came in 20k, 50k or 200k ohms variations. Could not find anything that had 5k ohm and was rated for 12 volts.
Then it occurred to me that there must be a digital potentiometer in the console or on the power supply to feed a signal to the MC-60.
Looking at the connector on the PB-121 board I see the following:
It kind of makes sense to me that an opto-coupling transistor is used to isolate the PB-121 from the MC-60. I would certainly want that isolation on my Arduino.
Here is the schematic for the 4N35
When I don’t understand things I stall for time and draw pictures. So here is my drawing of the circuit above:
The schematic states that there is 12 volts between the red and black lines and 0-12 volts between the blue and black lines.
The following is what I infer is going on with this circuit:
When current flows to the transistor, then the red and blue lines are connected. At this time there would be 12 volts between the blue and black wires. (Or at least the blue/black circuit looks the same as the red/black circuit)
When there is no current to the transistor, then the red and blue lines are not connected and there is 0 volts between the blue and black wires.
If the PWM signal into the transistor is at 50% then the average voltage between the blue and black wires would be 6 volts.
I don’t know what the two resistors do. For now I will assume that they are part of the analog circuit magic to even out the signal.
Does this make sense to someone smarter than I?
Do I just blindly pull the components off the circuit board and move them to my Arduino?
What is the voltage I need to apply to the Anode/Cathode to get this to work? Will 5 or 3.3 volts do the job? Or is the current important and I need to put a resistor in the circuit to produce the desired current?
Is there something I am missing?
What frequency should I use for the PWM?