pwm schematic help required please?

[Doddy]

Nothing more fun than trying to diagnose boards from photos :)

You're right - Pins 1+2 look to be the local +V supply from the on-board switched-mode PSU, and pin 4 is the ground. Now, pin 3 is connected to the cathode of the opto-isolator (U4), with the anode pulled up to +V via R5 (4k7?, can't make out band 3/4, think its [4][7][0][10^1]... could be wrong) - the output from the opto isolator heads off to the vertically mounted control board - which looks to be the brains of the speed control. That basically means that pin 3 is pretty much all you can use to control the motor - it could be basic PWM, or some other form of digital signalling - unclear, and would need images of front and back of vertical board to even begin to guess). What it almost certainly isn't - is any form of analogue control on the pin-3 input, so I'd bin the pot. I did wonder if the pin-3 was an spindle encoder feed-back input but the absence of any other connector would tend to suggest not.

Connecting 3-4 spins the motor?, yeah, can see that. So presumably it is a PWM input. What you need now is a PWM controller that generates an inverted output (e.g. more "Space" than "Mark" as the demand increases). The problem is that it's hard to guess what the PWM frequency should be to generate the M/S signal. Something like that would be easy to knock up on an Arduino if you have the inclination - and would allow you to explore the speed range easily. That'd be where I'd be heading next in the absence of any data on the board. You could instead experiment with (I assume you're using Mach3?) the PWM output from the BoB (if available) - don't use the analogue output. Or, re-map the Mach PWM output pin to an unused axis on the BoB and use that to drive the PWM input to the speed controller.

You say you can get the motor to Start AND Reverse?, there must be some other control/switchgear to support that - this only allows a variable 0-XX VDC to the supply, so it should be unidirectional. Is there other switchgear? (heading off on a tangent since this doesn't really address the speed control issue).

Rough-arse sketch of the signalling around the ribbon...



It's only a partial schematic after the opto-isolator, what I'm trying to get at is that the only control you have is the signalling between pin 3 and 4 of the ribbon - that's where you have to introduce a digital PWM signal.