PDA

View Full Version : Recommended DAC please?



Swarfing
12-09-2011, 12:44 AM
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.

Thanks

Paul

Jonathan
12-09-2011, 07:25 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?

Swarfing
12-09-2011, 08:55 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

Jonathan
12-09-2011, 06:54 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...

Swarfing
12-09-2011, 07:28 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.

m_c
13-09-2011, 02:22 AM
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.

Swarfing
13-09-2011, 01:52 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.

cheers guys

Paul

m_c
13-09-2011, 03:07 PM
I just done a bit searching, and it would appear from a couple references, that the older spindleV2 board was cheaper.

Robin Hewitt
13-09-2011, 05:31 PM
Is it worth mentioning that a DAC is a simple resistor ladder, ADC's are the tricky blighters :whistling:

Swarfing
13-09-2011, 06:53 PM
LOL! normally harder to climb ;-)

Jonathan
13-09-2011, 07:10 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:

http://uk.farnell.com/jsp/search/productdetail.jsp?sku=8454647

(There's probably cheaper ones that are adequate - that's just one I've used before so I know it works easily!)

Swarfing
13-09-2011, 09:14 PM
No worries mate i have plenty of Dill's and QFP's suitable for the job :-)

Thanks