Home machine. Lathe with Mach3 turn. Spindle speed input used to work with a different BOB board but now it is erratic. It will show spindle speed, run up to approx 950rpm with my variable speed motor. When I turn the variable speed motor down, it will decrease slowly with the chuck speed, but then jump approx 400rpm higher?? Example it was sitting at 457RPM, then bumped up to 857rpm uncommanded. This is indication only.

I have a hall sensor installed on my lathe spindle. Its connected to the 12vdc on the BOB, using the ground side of the inputs of the BOB. And each time the sensor senses a pulse, is pulsing 12vdc into pin 10. As I understand it, these pins are for the homing switches and are looking for an earth. Is this perhaps where I am going wrong? If so, I guess I will build up a transistor set to do just that.

But curious if anyone can offer a solution first?

You need the de-bounce in config set to the minimum for the spindle.

Just when I think I have looked at everything, someone comes up with a possible solution. Thanks. I actually thought it might be because I am bumping +12vdc straight into the board instead of what its normally looking for. I will try that.

Out of interest I mentioned it to Stepperonline who I bought the BOB off - their response was its not possible, the board was not made for it.

I dont know much about the computer side of the operation, but do think that the input pins off the BOBs are just isolated connections directly into the serial port with opto couplers. Is this correct? So the 12vdc I am pulsing into the board, is converted to 5vdc, and then pulsed directly into the serial port, which Mach 3 sees. Am I wrong?

Hi Graham,

Sorry, can you expand on the debounce settings? Like, are you saying to make them zero? I have tried everything I can think of, even to the point of making a transistor circuit to further isolate the input pulse from the board. The RPM still shows on Mach 3, but does the same, erratic. Go up past 900RPM, it will drop to 450 rpm and then start going up from there as if normal. But the actual speed is probably at 1200.

My hand held tacco is broken, I am waiting for a replacement to arrive but still, I should be able to get this going.

I have replaced the encoder, rewired it even. How I see it, the BOB is just a straight through input into the serial port of the PC with an opto coupler in the middle. Is is not possible I need to change my BOB to one that works with a spindle input? I am unsure where to go with this now. B

This was dumb. I sorted it this morning.

1 - The hall effect module I replaced with one that was faulty out of the box. Hey, it was an Aliexpress piece. What I do with them on orders below $4 is buy several so at least one goes. Haha. I should have tested it. So replacing it didnt sort my problem.

2 - The hall effect module that was installed on the lathe had a cold solder joint on the output pin.

3 - Resoldered, installed, satis.