pwm schematic help required please?

[Doddy]

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.