pwm schematic help required please?

Quote:

---

Originally Posted by Doddy

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?Attachment 25495

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

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.Attachment 25496

Jools

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?

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

Attachment 25497

John

Quote:

---

Originally Posted by john swift

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

---

Thanks John, that's very clear and I think supports my advice above.

Quote:

---

Originally Posted by Doddy

Thanks John, that's very clear and I think supports my advice above.

---

Thanks for the replies gents - good to have people at least trying to help me despite my limited electrical understanding!

Havent had much time to look at it for a couple of days, but having read the reply about measuring the output voltage with the meter set on ac, it does indeed read 0.2v ac when programmed s1000 via mach 3 (assume that means its a result of pwm "wave"?)

Attachment 25498

As you can see pwm is activated to output on p1

Be bold :) Just wire it up. There's not much that you can do via ribbon #3(+) / #4(-) to cock it up. #3 to P1, #4 to gnd.

Quote:

---

Originally Posted by Doddy

Be bold :) Just wire it up. There's not much that you can do via ribbon #3(+) / #4(-) to cock it up. #3 to P1, #4 to gnd.

---

Well, tried that, (pwm to wire 3) the spindle fires up and goes to 3500rpm (when s250 m4 is mdi input on mach3)

Altering the s value makes no difference to the spindle rpm, (i.e. s25 gives the same 3500rpm!) although the pwm output voltage does alter accordingly...

any more ideas?

Quote:

---

Originally Posted by Tel 27

Well, tried that, (pwm to wire 3) the spindle fires up and goes to 3500rpm (when s250 m4 is mdi input on mach3)

Altering the s value makes no difference to the spindle rpm, (i.e. s25 gives the same 3500rpm!) although the pwm output voltage does alter accordingly...

any more ideas?

---

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.