PLC Stamp input voltages 24v vs 5v.

jeffjohnvol

If I use a PLC Stamp, I have several switches that are already at 24 volts, which according to the PLC manual is the normal High value ("on"),, but if I use other switches that are tied to 5 volts, will the PLC recognize it as high, or do I need to use a transistor to convert the 5 volt value to 24v?

Chris Savage

Jeff,

It’s an opto input so it still should work. I would try it. At a lower voltage you certainly won’t damage anything. You can use DEBUG to monitor the status of the inputs. I hope this helps. Take care.

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Chris Savage
Parallax Tech Support

jeffjohnvol

Chris Savage (Parallax) said...
Jeff,

It’s an opto input so it still should work. I would try it. At a lower voltage you certainly won’t damage anything. You can use DEBUG to monitor the status of the inputs. I hope this helps. Take care.

Thanks Chris, I'll give it a shot.

Nice garage parking project, btw.· You ought to market that.

MinimumWage

Hi Guys,

I'm working with a Stamp PLC right now for a project at work. While I had it on the bench this morning I tested how it worked with a 5V signal, and while the LED on the PLC enclosure flickered a bit I couldn't get the stamp·input to change state. The lowest voltage that gave me reliable switching was around 6.5V. I think the Stamp PLC manual mentions having inputs in the range of 12-36V, although from the text I wasn't sure if this was a recommendation or just an observation that 24V sensors would fit somewhere inside that window.

Mike

jeffjohnvol

MinimumWage said...

Hi Guys,

I'm working with a Stamp PLC right now for a project at work. While I had it on the bench this morning I tested how it worked with a 5V signal, and while the LED on the PLC enclosure flickered a bit I couldn't get the stamp·input to change state. The lowest voltage that gave me reliable switching was around 6.5V. I think the Stamp PLC manual mentions having inputs in the range of 12-36V, although from the text I wasn't sure if this was a recommendation or just an observation that 24V sensors would fit somewhere inside that window.

Mike

Thanks Mike.· I read that same line (12-36) but wasn't sure myself, until I just reread it.· Rereading it, I guess it means that 12-36 volts will produce 0 at the stamp pin, and 0 at the PLC input will produce 5 V on the stamp pin.

MinimumWage

Right. Still, it might be worth a test when you get your PLC. It seems like 5-6V is just on the threshold of making the input switch·on my unit. Maybe yours will beat the spec?

jeffjohnvol

I think I'll play it safe and try to get some full voltage to the input.

Can anyone tell me if the attached circuit would do what I need (create a 24 volt output with a 5 volt input) ?

jeffjohnvol

BTW, on that circuit I attached, if anyone knows a simpler one, that would be great.

stamptrol

Not to quibble....the transistor should be an NPN type with emitter to ground.

A compact alternative to separate transistors are ULN2003's which can be had with a base resistor built in. Plus getting 7 transistors in a DIP package

Cheers,

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Tom Sisk

http://www.siskconsult.com
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jeffjohnvol

stamptrol said...
Not to quibble....the transistor should be an NPN type with emitter to ground.

A compact alternative to separate transistors are ULN2003's which can be had with a base resistor built in. Plus getting 7 transistors in a DIP package

Cheers,

Okay.· I have the August 1995 N&V article that talks of using Switching Transistors that talks of the ULN2003.· I assumed the supply voltage was 5 volts.· Would I be able to use 24 volts, with 0-5 volts on the input to get 24V out?

And on the quibble, please correct me, since my electronics are rusty, but wouldn't switching PNP to NPN just change the polarity of the result?

EDIT: Nevermind, I googled a datasheet on the ULN2003, looks like that would do the trick.· I much prefer the IC's over individual components.

Post Edited (jeffjohnvol) : 4/19/2007 8:07:42 PM GMT