# A lump in cord design...

Discussion in 'Electronic Design' started by Howhurley, Sep 22, 2007.

1. ### HowhurleyGuest

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)

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

2. 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.

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

4. 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

Howhurley

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

3. ### Fred BloggsGuest

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