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A lump in cord design...

I've got a situation I hope one of you wonderful circuit designers can help me with. In a three wire (+24VDC, DC GND, and a 12-24 signal from a PLC, perhaps 100 ms in length) I need to come up with a monostable ramp signal from 0 to 10 volts, no more than 10-15 mA, approximately 1 sec in duration, adjustable in slope.(gain)

Three thoughts I had were:

  1. A simple RC circuit, (non-linear, I know, but buffered with a cheap op-amp front and back to even things out)

  1. A 555 timer/oscillator to charge a cap until it hit a certain point on an op-amp comparator which discharged the cap...the voltage level would then be tracked by a unity gain follower and actually be my output.

  2. A simple 8 bit d-a, charged by a oscillator circuit,

  1. Of course, a simple rabbit or pic microcontroller...but that's for the future.

Any ideas? I'm a sales guy that sells industrial stuff, and some of the things I sell are ideas on how to do things. I quoted a job, assuming that this type of thing was available, and, well, you know about assuming things.

Howhurley

Reply to
Howhurley
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I'd use an op-amp as in integrator (like your RC idea, but you'll get a linear output) and then either build the monostable "part" out of discrete transistors or use some 555-like device if you can get one for 24V. I'm trying to avoid your needing a voltage regulator here, although if your 24V isn't that well-regulated, it'd affect the ramp rate... which could actually be good or bad, depending on whether you want the adjustment to be in volts/second or percent of full voltage output/second.

The Art of Electronics has all you need to know about building op-amp integrators if you don't already have a reference.

---Joel

Reply to
Joel Kolstad

Well you need to tell us the relationship between the "12-24 signal" from the PLC and the slope/duration of the ramp output, dontcha think? And what does "lump in chord" have to do with anything? We can't read your mind.

Reply to
Fred Bloggs

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