pwm schematic help required please?

[Tel 27]

You say:-

"PWM to wire 3", and separately, "although the PWM output voltage does alter accordingly".

What have you wired to the speed controller pin 3?, the PWM ("...output voltage does alter...") or the P1 pin?


EDIT: Sorry, I appreciate I seem to be repeating myself, without explanation:-

The PWM ("Pulse Width Modulation") output from the PC is typically Pin1 of the parallel port - and you've confirmed this is how it's assigned in Mach. Okay so far. This pin/signal is a digital signal, alternative between On ("Mark") and Off ("Space"). The ratio of Mark/Space defines the PWM value, essentially a per-unit measure from 0 to 1 for Off to Full-speed. Increase the Mark ratio vs Space and you denote a speed increase.

Pin 1 of the BOB is connected (using the schematic from John), to two inputs on one of the octal transceivers (74x245) - inputs B2 & B3. The "DIR" direction pin on that chip is set to transfer from port B to port A. So the PWM input appears on A2 & A3. A3 is connected to the connector P1 on the BOB, and as such presents a buffered copy of the digital PWM (Mark/Space signalling) from the PC. It is this that needs to be connected to the speed controller. The other port, A2 is connected to an opto-isolator, through to the op-amp (half of LM358) which is configured as an integrator - it converts the Mark/Space ratio to an analogue voltage. This would be used for an analogue input to a speed controller (but NOT a digital PWM input).

It's for this reason that I'm asking you to confirm which PWM signal you have connected to the speed controller - because you refer to the PWM signal in an analogue sense.

Unfortunately much of what you are telling me is going over my head!

This is how its currently wired:



Does the fact the altering of the pwm voltage through mach3 commands makes no difference to the output from the controller board to the motor indicate a problem with the board itself?

[Doddy]

Unfortunately much of what you are telling me is going over my head!
Does the fact the altering of the pwm voltage through mach3 commands makes no difference to the output from the controller board to the motor indicate a problem with the board itself?

No. In fact it's exactly as I'd expect from the information that you've supplied to date. If you was to set the speed to 10% of max (assuming you've calibrated it) then I'd expect the spindle to be OFF. And above about 25% I'd expect it to be full-on. This is simply the (wrong) application of the analogue output from the BOB to the opto-isolator input to the speed controller, which instead expects a PWM input.

Simply. Connect the BOB output pin P1 to ribbon Pin 3. Connect the Ground used for the BOB to ribbon Pin 4. There is no need for any of the resistors.

Rough-arsed sketch - the PC output pin-1 is a digital PWM output. The BOB routes this to two different outputs - the BOB "P1", which is a facsimile of the PC output - and is the signal you need. There's also an on-board (the BOB) integrator that converts the PWM to the analogue output, that you don't need. Your speed controller takes a digital PWM input and uses this either to generate the analogue drive to the onboard speed controller, or simply uses this to drive the onboard MOSFET to drive the spindle. Regardless, the important bit is that the speed controller around the pin 3/4 terminals is designed around having a Digital PWM input, and NOT an analogue input (which, confusingly, is derived from a PWM source)

[Tel 27]

No. In fact it's exactly as I'd expect from the information that you've supplied to date. If you was to set the speed to 10% of max (assuming you've calibrated it) then I'd expect the spindle to be OFF. And above about 25% I'd expect it to be full-on. This is simply the (wrong) application of the analogue output from the BOB to the opto-isolator input to the speed controller, which instead expects a PWM input.

Simply. Connect the BOB output pin P1 to ribbon Pin 3. Connect the Ground used for the BOB to ribbon Pin 4. There is no need for any of the resistors.

Rough-arsed sketch - the PC output pin-1 is a digital PWM output. The BOB routes this to two different outputs - the BOB "P1", which is a facsimile of the PC output - and is the signal you need. There's also an on-board (the BOB) integrator that converts the PWM to the analogue output, that you don't need. Your speed controller takes a digital PWM input and uses this either to generate the analogue drive to the onboard speed controller, or simply uses this to drive the onboard MOSFET to drive the spindle. Regardless, the important bit is that the speed controller around the pin 3/4 terminals is designed around having a Digital PWM input, and NOT an analogue input (which, confusingly, is derived from a PWM source)

confused really is the term that springs to mind!

how exactly would I calibrate the speed?

[Doddy]

Just do this:-
Connect the BOB output pin P1 to ribbon Pin 3. Connect the Ground used for the BOB to ribbon Pin 4. There is no need for any of the resistors.


To answer your question:-
Google Mach3 Spindle Settings to find out how to setup. What I meant by "calibrate" was perhaps misleading, my fault.

My intent, when you issue lets say a speed of S1000, that the actual speed would be a ratio of the commanded speed vs the maximum spindle speed - so if the max spindle speed was set within Mach to 2000rpm, then a S1000 command would set the PWM output at 50% Mark/Space. If the max spindle speed was set within Mach at 4000rpm, then the same S1000 command would set the PWM output at 25% Mark/Space ratio. My comment was to ensure that the commands that you issue to test the speed control would respond with a sensible response from the PC/machine.

[Tel 27]

Just do this:-
Connect the BOB output pin P1 to ribbon Pin 3. Connect the Ground used for the BOB to ribbon Pin 4. There is no need for any of the resistors.


To answer your question:-
Google Mach3 Spindle Settings to find out how to setup. What I meant by "calibrate" was perhaps misleading, my fault.

My intent, when you issue lets say a speed of S1000, that the actual speed would be a ratio of the commanded speed vs the maximum spindle speed - so if the max spindle speed was set within Mach to 2000rpm, then a S1000 command would set the PWM output at 50% Mark/Space. If the max spindle speed was set within Mach at 4000rpm, then the same S1000 command would set the PWM output at 25% Mark/Space ratio. My comment was to ensure that the commands that you issue to test the speed control would respond with a sensible response from the PC/machine.

Well, that didnt work either, I'm getting to the end of my tether with it now, got a few things I'd like to do with it looming large (been calling in favours elsewhere too long now)
Is there anyone in the UK I could take it to?, (preferably in the North East but it's easily transportable in my van)
Happy to pay someone for their time....

[Voicecoil]

If you can't find anyone over in the NE, I'm not too far away ont' t'other side of the Pennines - not exactly on your doorstep but at least the roads are good. Shame, I was over your way for a guitar show back at the end of March, could have dropped round and sorted it.