INterface stamp with 24v logic

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hello all,

I would like to use my stamp to control a VFD (variable frequency drive 220v three phase). This happens to be 24v control logic 30ma max. It has the option of sourcing or sinking.

My solution was to use a darlington array. Stamp input pin to pin 1, vss to pin 9 (darlington ground uln2803a), VFD 24v to pin 10, vfd gnd to pin 9 on darlington. VFD control pin to pin 2 on darlington...

First, do I have this correct? second will this keep my 24v and my 5v separate. Third, how do i prevent noise from entering my 5v system? am i on the right track?

Thank you,

DP

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DP
(ΜΟΛΩΝ ΛΑΒΕ)

[stamptrol]

I don't have the circuit of the uln2803a right at hand, but basically, set your drive controls as sinking and use the transistor to pull the control line to 0v.

You can also use an opto coupler to do the same thing. The Stamp pin drives the LED in the optocoupler and its transistor pulls the drive control line to 0v. It also provides the best isolation. I've also used small reed relays to isolate the Stamp from the drive.

Similarly, if the drive has signals you want to get back to the Stamp, (like "At target Speed") let the drive signal operate an optocoupler's LED and use the transistor to switch 5 volts to the Stamp.

Cheers,

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Tom Sisk

http://www.siskconsult.com
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