pwm schematic help required please?

[Tel 27]

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.

The direction is switched via relays on the other board (I assume as they click when direction is programmed), the voltage from the breakout board when I mdi input s240 m4 is 0.5v, then at s500 measures 1.0v, at s1000 2.0v etc etc.

Are you advocating connection of the + PWM lead from the breakout board go to wire 3 and the other pwm to wire 4?

I did say electrics are not my field!

[Doddy]

The direction is switched via relays on the other board (I assume as they click when direction is programmed), the voltage from the breakout board when I mdi input s240 m4 is 0.5v, then at s500 measures 1.0v, at s1000 2.0v etc etc.

Are you advocating connection of the + PWM lead from the breakout board go to wire 3 and the other pwm to wire 4?

I did say electrics are not my field!

Hmmm, looking at that you might want to take up Italian cooking, to make sense of that spaghetti :). <-- intended with tongue in cheek

Okay, I don't know your BoB - but looks pretty generic. That makes me think that the "outputs" from the controlling PC will be buffered with the two large chips (74HC244s?) - they'll be able to drive the PWM output low enough to activate the opto-isolator, and so *should* work (or at least not blow anything up). Suck it and see. My other comment was thinking that if, and I don't know about this, but if the BoB doesn't output the standard PWM pin out, but instead only provides the resulting analogue drive, then instead of trying to route the standard PWM, use the other outputs that are associated with the typical 4/5 axis drives on the BoB - as these are easily available (and from within Mach its easy to remap the PWM output to any pin).

My conversation about arduinos is simply to take an unknown (mach) out of the equation to help better understand how to drive the speed controller, but I'm presuming - perhaps too much - that that's in your interest/comfort zone. It's nothing to do with CNC but would be a great way to test the board in (almost) isolation.

[Tel 27]

Hmmm, looking at that you might want to take up Italian cooking, to make sense of that spaghetti :). <-- intended with tongue in cheek

Okay, I don't know your BoB - but looks pretty generic. That makes me think that the "outputs" from the controlling PC will be buffered with the two large chips (74HC244s?) - they'll be able to drive the PWM output low enough to activate the opto-isolator, and so *should* work (or at least not blow anything up). Suck it and see. My other comment was thinking that if, and I don't know about this, but if the BoB doesn't output the standard PWM pin out, but instead only provides the resulting analogue drive, then instead of trying to route the standard PWM, use the other outputs that are associated with the typical 4/5 axis drives on the BoB - as these are easily available (and from within Mach its easy to remap the PWM output to any pin).

My conversation about arduinos is simply to take an unknown (mach) out of the equation to help better understand how to drive the speed controller, but I'm presuming - perhaps too much - that that's in your interest/comfort zone. It's nothing to do with CNC but would be a great way to test the board in (almost) isolation.

Truth be told the whole electrical thing is outside my comfort zone!

I've no problem with programming and machining, (been doing that since I left school in 79') but electrics are a mystery to me!

This is a sketch of how the potentiometer was previously wired up - I think its incorrect, looking at previous comments, there is NOTHING going to wire 3 (this was merely cut off), and it sounds like wire 3 is the ONLY way the PWM output can connect to the controller board? (with or without the potentiometer in the circuit)

I'm at a bit of a loss here - is there anyone in the UK who could take a look at it for me?

[Jools]

I've just done this to my MX3660 BOB and driver. The thread is here https://forum.linuxcnc.org/38-genera...-output-solved have a read through and then see how it stacks up to yours. On mine in the end I removed the whole POT circuit board and wired mine straight to the wires. If you have a spare output you can get the spindle to reverse too incase you want to tap.

Jools

[Jools]

If you measure voltage across the middle and right hand pin on the POT this should go from zero to 5v (or what ever the voltage in is) The missing central wire from the pot is the variable part of the voltage that controls speed. I would think that this should be wired up to your wire four from previous posts.

On mine I simply took out the pot and wired the PWM 10v in to the right hand pot connector (wire 1) (So I took my power from the machine) . The left hand ground to ground (wire 4). and the wiper to wire three. This controls mine perfectly.

Page 8 from this BOB manual helped me http://cnc4pc.com/Tech_Docs/C11GS-R1_1_USER_MANUAL.pdf though your's might differ. Though it may be the same.

This is my BOB's wiring digram though it was the same to my machine not using a VFD as they show.

Jools

[Doddy]

The issue here is that the OP's spindle speed control looks to be a digital PWM input drive, not an analogue input voltage. I accept this is somewhat different to the standard option on many speed-controllers on a standard spindle inverter driver.

In using the BOB the OP has inadvertently adapted the PWM output from the PC to an analogue voltage.

The Speed Controller looks to use only a PWM input.

The easiest test now would be to try to source the PWM output from the PC (looks to be available on pin 'P1' output on most BOBs), and feed this to the pin-3 of the speed controller. Connect BOB ground to pin 4. If this works at all - if the speed range is inverted (low = high speed, high = low speed) then write to confirm.

Or, if the PWM output from the PC (into the PWM input on the BOB) then look to remap via Pins/Ports from Mach to a different output than '1', and try again.

The original Pot set-up looks (a) to be mis-wired, and (b) likely intended to be a potential divider to scale input - whether this was PWM or analogue to a lower voltage/current. If the value of R5 is 4k7 then this just isn't needed for the opto-isolated input for any supply up to 10V (If ~= 4mA on the opto-isolator LED at 10V input). BUT, unless you get a PWM signal into it I doubt from the quick look at the board that this will give anything other than On/Off. The OP needs a PWM source.

EDIT:

OP: On the image of your BOB - what's the label on the fourth pin from the left on the top edge of the board (after the Red/Red/Yellow cables)? - Is that P1?

[john swift]

looking at the second photo in post 8
the BOB looks like this BOB



John

[Voicecoil]

The direction is switched via relays on the other board (I assume as they click when direction is programmed), the voltage from the breakout board when I mdi input s240 m4 is 0.5v, then at s500 measures 1.0v, at s1000 2.0v etc etc.

It would be instructive to measure on that same point with your meter set to AC rather than DC whilst inputting s240, s500, s1000 etc. and see what you get: if there's a decent (a volt or two) AC level there at s1000 then it's a PWM output, if not then as Doddy says it will have been converted into DC. A DC meter will average out a PWM signal and give a reading corresponding to the duty cycle:

The AC level will be zero at 0% and 100% duty cycle, but doesn't vary so much in the middle range.