Re: [CAD_CAM_EDM_DRO] Re: Controlling VFDs from your PC?

On Sun Feb 10 02:04:55 2002, stevenson_engineers, <machines@...> wrote:

>>--- In CAD_CAM_EDM_DRO@y..., "audiomaker2000" <audiomaker@s...>
>wrote:
>> Thanks guys.
>>
>> That makes me ask....
>>
>> How do you produce an analog signal of varying voltage from one of
>> your computer's ports?

You tell the computer to feed your device a number, (into a latch for instance),
and run the latch output into an R2R network. You can use the level info thus
derived, to control the VCO stage of a PLL for variavle frequency output. Or,
you could do that once, feeding instead, an up/down counter, and feed the
counter with occaissional count up/down pulses, the output again feeding the
R2R/PLL.

I don't know much about this, but from what

>> I've read, most pins produce either a "high" or "low" condition
>>which
>> I can see triggering a relay, but not a variable "pot".
>> I suppose this is normally taken care of by the complex electronics
>> of a CNC machine, but I am retrofitting with a system that appears
>>to
>> only produce step and direction signals.
>> So how do you turn your computer into a "dimmer" instead of
>> a "switch"?

Pulse width modulation. If for instance, you have a logic gate or inverter type
RC oscillator, you can change the pulse width by running a pot feeding two
diodes off the ends of the pot. The two diodes are oriented so that one is,
"pointing", in the oposite direction to the other, Tie the free ends of the
diodes together, and drop the whole shebang into your RC feedback loop. You can
use the pot to control the pulse width, independent of the frequency.

Bill

>> Any ideas?
>
> Sean,
>What system are you using?
>I ask because AHHA is able to output an analog signal 0 - 10V on it's
>card to control a VFD. You just take two wires from the port to the
>VFD and whatever you program in is then sent to the VFD as a
>referance voltage.
>
>John S.

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