Some Sort of Multivibrator

--- That won't do it, Jim.

What he wants is something that goes high when the input goes high, stays high as long as the input does, and then when the input goes low stays high a little longer before it times out.

EXCEPT, that if the input should go high while the device is timing out the thing will stay high until the input goes low long enough for the output to time out.

Like this:

IN>--+------------A | OR Y-->OUT +-[DIODE>]-+-B | | +---[R]----+ | [C] | GND>------------+------->GND

JF

Did you test my circuit before commenting ?:-)

I don't think so.

Take another look... I added a changed excitation.

Note that timing begins at the _fall_ of the input. If Input rises again _before_ time-out, time-out is reset.

...Jim Thompson

Maybe you're quibbling about the capacitor dump time?

But I doubt that "DfromBC" is doing any super fast stuff.

...Jim Thompson

No problem!

There's probably some way to do exactly this with an existing monostable chip, but I haven't been able to locate it.

Since I only do chip stuff, I'm always rolling my own, so I'd typically have an open drain doing this kind of capacitor-dumping work.

...Jim Thompson

No speedy stuff this time. I haven't checked yet but I think the minimum source signal pulse time is a few mS. That'll be plenty of time to decharge the cap in your design. Btw..interesting design..

Another alternative is:

If I get into narrow input pulses, then trigger/latching circuits are better.

D from BC myrealaddress(at)comic(dot)com BC, Canada Posted to usenet sci.electronics.design

When you have a need for speeds comparable to gate prop delays, post again. I have my ways ;-)

...Jim Thompson

Cool :)

D from BC myrealaddress(at)comic(dot)com BC, Canada Posted to usenet sci.electronics.design

Isn't this what you want?

Version 4 SHEET 1 908 840 WIRE 256 304 224 304 WIRE -320 320 -336 320 WIRE -256 320 -320 320 WIRE -96 320 -192 320 WIRE 64 320 -96 320 WIRE 160 320 64 320 WIRE -320 368 -320 320 WIRE -96 368 -96 320 WIRE 64 368 64 320 WIRE -320 496 -320 448 WIRE -208 496 -320 496 WIRE -96 496 -96 448 WIRE -96 496 -208 496 WIRE 64 496 64 432 WIRE 64 496 -96 496 FLAG -208 496 0 FLAG -336 320 in IOPIN -336 320 In FLAG 256 304 out IOPIN 256 304 Out SYMBOL diode -256 336 R270 WINDOW 0 32 32 VTop 0 WINDOW 3 0 32 VBottom 0 SYMATTR InstName D1 SYMATTR Value 1N914 SYMBOL res -112 352 R0 SYMATTR InstName R1 SYMATTR Value 10k SYMBOL cap 48 368 R0 SYMATTR InstName C1 SYMATTR Value 1µ SYMBOL voltage -320 352 R0 WINDOW 0 -32 56 VBottom 0 WINDOW 3 -210 -13 Invisible 0 SYMATTR InstName Vtest SYMATTR Value PULSE(0 5 0 1u 1u 10m 20m) SYMATTR SpiceLine Rser=100 SYMBOL Digital\\\\schmitt 160 256 R0 WINDOW 3 -23 127 Left 0 SYMATTR InstName A1 SYMATTR Value Vhigh=5 Vlow=0 TEXT -96 272 Left 0 !.tran 100m TEXT -288 120 Left 0 ;Supply a 5V input pulse at IN. Output is a pulse\\nlengthened by R1*C1*ln(2.5/4.4)

Yup .. Kinda like a AM detector circuit but with square out.

D from BC myrealaddress(at)comic(dot)com BC, Canada Posted to usenet sci.electronics.design

---+------+---------+--- vcc | | | | | . . . .|. . . . | | . VCC(8) . | | .___ . | `---RES(4) OUT(3)-------- out [R] . 555 . | .---TH(6) DIS(7)---- O/C out | | .__ . +------+---TR(2) CV(5)-- | | . . | | . GND(1) . / | . . . .|. . . . |/ | | in --[R]--| ===== | |\\| | | ~\\ | | | | | --+------+---------+ gnd

almost all in 1 chip. you could use a half a 556 instead of the transistor and do it in one chip. (input tp TH,TR of of the other half, DIS to where the collector is, if the power-on pulse is an issue more the ground end of the cap to VCC

input goes high 555 output goes low, I've seen a CMOS 555 survive this for short periods.

input goes low 555 output goes high.

that's not going to work.

Looks like the 555 is just used for hysteresis. The 555 can probably be replaced by a single comparator with hysteresis or a schmitt gate.

Variations like that are fine for my app due to the signal pulse width being a few mS.

D from BC myrealaddress(at)comic(dot)com BC, Canada Posted to usenet sci.electronics.design

Strange - you would't put a diode on the 555 output and a cap on the input? Me culpa, I assume too much. I should have drawn it.

Ed