View Full Version : Recommended DAC please?
11-09-2011, 11:44 PM
Guys i have been looking franticly for a thread on here that showed a link to an ebay item for allowing speed control of the vfd from Mach3/ EMC2. It was only about £10 does anybody remember it or can recommend one? The VFD in question is 2.2kw chinese job and matching VFD.
12-09-2011, 06:25 AM
I think you can use the PWM output from mach3, possibly with a capacitor/resistor to smooth it. Use the input for the potentiometer on the VFD.
Worth trying before buying anything?
12-09-2011, 07:55 AM
Jonathan that is a way i would prefer not to go and would rather use a dedicated DAC for the job. I would stll use pwm control settings in EMC2
12-09-2011, 05:54 PM
There's an option on the VFD to read 3 digital inputs to give 8 different speeds. If you've got enough I/O (i.e. another parallel port) then that could work. Might take a bit of fiddling to get EMC to provide the correct outputs? Not sure...
12-09-2011, 06:28 PM
Yes i have the same but would feel better about using ramp control of the spindle. This way i would ever need to remember top and bottom speeds.
Most VFDs I've seen require 0-10VDC on the potentiometer terminals, but check your manual to be sure.
What you need is something like the Spindle V3 (http://www.diycnc.co.uk/html/spindle_v3.html) from diycnc.
13-09-2011, 12:52 PM
This is practically the same as the one i was looking for, the only difference was the price £10 instead of £21 with free p&p. The option for now is o just wire manual controls up and build my own circuit. I've just ordered another Par card so that i can dedicate the pins for external controls etc in a single package. we will see where we go from there.
I just done a bit searching, and it would appear from a couple references, that the older spindleV2 board was cheaper.
13-09-2011, 04:31 PM
Is it worth mentioning that a DAC is a simple resistor ladder, ADC's are the tricky blighters :whistling:
13-09-2011, 05:53 PM
LOL! normally harder to climb ;-)
13-09-2011, 06:10 PM
Is it worth mentioning that a DAC is a simple resistor ladder
I've tried making DACs with R2R resistor ladders. They were OK, but not especially accurate due to the way the small errors accumulate. If you buy the resistors in a reasonable quantity then you can spend a bit of time with a meter matching them which can help a lot.
Probably easier just to buy the IC. Something like this:
(There's probably cheaper ones that are adequate - that's just one I've used before so I know it works easily!)
13-09-2011, 08:14 PM
No worries mate i have plenty of Dill's and QFP's suitable for the job :-)
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