Variable motor control via pc -- Help--!

[SME]

Hello Group,

I have a variable motor controller board that is controlled by voltage.
I wish to control this board via my computer's printer port. Ideally using
CNC software such as EMC.
Any help would be very much appreciated.
The input has 3 wires lets say A B C.

Voltmeter Testing.

A and C = 12V Steady
A and B = Variable voltage 2.3 - 9.7 V Approx.
B and C = Variable Voltage 2.3 - 9.7V Approx.

When A + B carry low Volts, B + C are carrying high Volts and vice versa
(I.E. they complement each other and are relative adding up to the total of
12V)

The Higher voltage across B and C = Faster Motor Speed
The Higher voltage across A and B = Slower Motor Speed

So when B and C are reading max voltage the voltage to the motor is approx.
190V.

BTW this is off of a very old CNC machine.

What I am going to need to-do is have these voltages controlled via EMC + a
circuit to produce the above output voltages.

Does anyone have any idea what is required or what this circuit is called.

Congratulations on getting this far ... ;-)

TIA
Steve.

 

[Bob Masta]

On Thu, 6 Nov 2003 11:30:25 -0000, "SME" <nospam@nospam.com> wrote:

Hello Group,

I have a variable motor controller board that is controlled by voltage.
I wish to control this board via my computer's printer port. Ideally using
CNC software such as EMC.
Any help would be very much appreciated.
The input has 3 wires lets say A B C.

Voltmeter Testing.

A and C = 12V Steady
A and B = Variable voltage 2.3 - 9.7 V Approx.
B and C = Variable Voltage 2.3 - 9.7V Approx.

When A + B carry low Volts, B + C are carrying high Volts and vice versa
(I.E. they complement each other and are relative adding up to the total of
12V)

The Higher voltage across B and C = Faster Motor Speed
The Higher voltage across A and B = Slower Motor Speed

So when B and C are reading max voltage the voltage to the motor is approx.
190V.

BTW this is off of a very old CNC machine.

What I am going to need to-do is have these voltages controlled via EMC + a
circuit to produce the above output voltages.

Does anyone have any idea what is required or what this circuit is called.

Congratulations on getting this far ... ;-)

TIA
Steve.

It sounds like B is the wiper of a pot between A and C.
You might only need to supply a control voltage between
B and ground, and let the other input float. If that doesn't
work, then you will need to make a little subtractor circuit
to subtract your control voltage from 12 and present that
to the other lines.

You can generate the control voltage with your printer
port by building a little R-2R ladder DAC from 10K and
20K resistors. Use 1% tolerance if you want the full
8 bits of control. Depending on your port, you may need
to digitally buffer its output bits (74HC373 etc) before
they drive the resistors. This will give you 0-5V control,
which you can amplify to your desired range.

You can find some info on the buffered and unbuffered
ladder DACs at <www.daqarta.com/lptx.htm>. This
is intended for use with my Daqarta software as a
DAC (or ADC), but you can easily adapt to your needs.

Hope this helps!




Bob Masta
dqatechATdaqartaDOTcom

D A Q A R T A
Data AcQuisition And Real-Time Analysis
www.daqarta.com