Interfacing to 24VDC

youngdave

Dear All
I need to interface a 6142 comparator (running at 24VDC) to the Prop. The input to the comparator will be the standard 0 - 3.3V.
Is this just a matter of inserting a resistor between the Prop and the 6142 input. If so, what is the best value for the resistor? Or is it more complicated than this.
Any assistance appreciated.
TIA David Young

Post Edited (youngdave) : 9/14/2009 11:38:17 PM GMT

CounterRotatingProps

Hi Dave - you might want to edit in a subject line to get more attention - H

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Mike Green

1) You need to provide a subject for your thread. Use the pencil icon at the upper right corner of your 1st message.

2) You need to provide more information about what you're using, like a link to the datasheet for your comparator.

youngdave

Mike
Thanks.
The question is not so much about the 6142, it's about interfacing to a 24VDC device without wrecking my Prop.
TIA David Young

Peter Jakacki

We are confused Dave. Which chip is this? the MCP6142 which has a maximum supply of 7V? The inputs you state as being 0...3.3V so where does the 24V come in?

*Peter*

P.S. schematic? sketch? description? anything?

Rob7

Dave,
It is difficult to understand what what you want.
I have created a small opto-input and opto-output board for experiments that I preform and it works great, all you have to do is change the input resistor voltage value to the input board to match the voltage that you need .
The link shows 5 V input and 24 V output.
Hope this helps.
Here is the link: http://forums.parallax.com/forums/default.aspx?f=5&m=1343

Rob 7

Post Edited (Rob7) : 9/15/2009 4:05:28 AM GMT

youngdave

I've attached the circuit I wish to use.
I’m a bit uncertain about the common GND for the Prop and the 6142. Is this a problem?
TIA David Young

Peter Jakacki

Dave, can I just say that your circuit looks "weirdly wrong". What's with R7? Turn it down towards ground and you short out the battery and blow the pot!. Also, the Prop doesn't run on +5V either.

However, you don't need any current protection resistor FROM the Prop, only if you connected a higher voltage signal to it. Are you trying to do TENS stuff or what?

*Peter*

P.S. I think this is the circuit you are trying to draw. (slight revision)

Post Edited (Peter Jakacki) : 9/15/2009 12:17:05 PM GMT