Some Sort of Multivibrator

You may want to take a look at the good old CD4536 chip. This thing can be hooked up to do a very similar thing to what you are doing. With care you can also hook up an osc to the thing and use the chip also to divide down to the oscillation to a slower using rate. I've used this chip with a 32.768 KHz crystal to generate gate pulsed for a digitial tachometer circuit before one would do such things in an MCU.

- mkaras

It behaves as a monostable, ON time determined by R1/C1

-- "Electricity is of two kinds, positive and negative. The difference is, I presume, that one comes a little more expensive, but is more durable; the other is a cheaper thing, but the moths get into it." (Stephen Leacock)

Before someone pulls me up, it's R1C1. The slash was not intended to imply division

-- "Electricity is of two kinds, positive and negative. The difference is, I presume, that one comes a little more expensive, but is more durable; the other is a cheaper thing, but the moths get into it." (Stephen Leacock)

And makes it look like a monostable.

I've selected this chip:

Looking at the truth table on p.2, I don't see how the output can stay H for as long as the input is high.

I'm looking for Input Output L L (rest state) H H (as long as input H) Fall drop output after time delay time

I'm not sure how to use this the x221 chip.

Note: My posted ltspice circuit reacts to retriggering. I think the x221 doesn't react to retriggering.

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

You have chosen a non-retriggerable part.

You should use 74**123

...Jim Thompson

Aah! - now I see. I'd got your circuit bassackwards. Picked the wrong node as output (R1 - D1 cathode), it was a little obscure (to me at any rate). That gave me a falling edge triggered monostable. Using the node you intended as output it's a pulse stretcher.

I saw the hanging wire as just an edit remnant. I bet John did, too.

Sorry, my mistake. If you'd labeled the end of the wire, I'd have probably noticed, but that's no excuse, it does actually say "Vout" nearby.

I'll go wipe the egg off ;-)

The output is not supposed to oscillate when the input is held H for a long time. :(

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

It'll be great if the spice circuit can be done with 3 NOR or NAND schmitt gates.

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

My ltspice circuit does react to retriggers. C gets discharged for retriggering and stays discharged if the input is held high.

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

The output oscillates when the input is held high. :(

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

I guess that, at the time, John didn't know the input was expected to be held high. I know I didn't. Your SPICE simulation didn't suggest it, using, as it does a continuous pulse train.

Sorry about that.. I should have mentioned that the circuit is independent of the generator. iow..The circuit should work for any pulse duration.

My next post is another circuit based on JF's post.

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

On Sun, 15 Mar 2009 15:05:15 -0700, D from BC wrote:

--- Try this:

Version 4 SHEET 1 948 740 WIRE -928 -32 -960 -32 WIRE -464 -32 -928 -32 WIRE -352 16 -400 16 WIRE -464 32 -496 32 WIRE -352 48 -352 16 WIRE -496 64 -496 32 WIRE -496 96 -352 48 WIRE -352 112 -496 64 WIRE -496 128 -496 96 WIRE -464 128 -496 128 WIRE -352 144 -352 112 WIRE -352 144 -400 144 WIRE -352 160 -352 144 WIRE -288 160 -352 160 WIRE -464 192 -496 192 WIRE -352 208 -352 160 WIRE -928 320 -928 -32 WIRE -832 320 -928 320 WIRE -672 336 -768 336 WIRE -496 336 -496 192 WIRE -496 336 -608 336 WIRE -352 336 -352 288 WIRE -352 336 -496 336 WIRE -928 384 -928 320 WIRE -352 400 -352 336 WIRE -928 528 -928 464 WIRE -352 528 -352 464 WIRE -352 528 -928 528 WIRE -928 576 -928 528 FLAG -928 576 0 SYMBOL res -336 304 R180 WINDOW 0 36 76 Left 0 WINDOW 3 36 40 Left 0 SYMATTR InstName R2 SYMATTR Value 1e6 SYMBOL cap -368 400 R0 WINDOW 0 -38 31 Left 0 WINDOW 3 -56 56 Left 0 SYMATTR InstName C2 SYMATTR Value 1e-6 SYMBOL Digital\\\\or -432 -64 R0 WINDOW 0 -30 7 Left 0 SYMATTR InstName A4 SYMATTR SpiceLine trise 1e-6 tfall 1e-6 vhigh 5v SYMBOL Digital\\\\or -432 224 M180 WINDOW 0 -30 14 Left 0 SYMATTR InstName A5 SYMATTR SpiceLine trise 1e-6 tfall 1e-6 vhigh 5v SYMBOL voltage -928 368 R0 WINDOW 3 24 104 Invisible 0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR Value PULSE(0 5 .1 1e-6 1e-6 1E-3 .5 3) SYMATTR InstName V2 SYMBOL Digital\\\\or -800 256 R0 WINDOW 0 -30 7 Left 0 SYMATTR InstName A3 SYMATTR SpiceLine trise 1e-6 tfall 1e-6 vhigh 5v SYMBOL diode -608 320 R90 WINDOW 0 0 32 VBottom 0 WINDOW 3 32 32 VTop 0 SYMATTR InstName D1 SYMATTR Value 1N4148 TEXT -912 552 Left 0 !.tran 5 uic TEXT -280 160 Left 0 ;OUT TEXT -1000 -32 Left 0 ;IN

JF

On Sun, 15 Mar 2009 07:50:03 -0500, John Fields wrote:

Sorry..forget to mention that the circuit is supposed to work with any input pulse length.

At current, the circuit below uses a 14pin SOIC chip. I'm now trying to figure out a solution with less pins or a smaller chip.

The circuit below uses one quad NOR.

Version 4 SHEET 1 1092 680 WIRE 368 -160 -80 -160 WIRE -80 -96 -80 -160 WIRE 32 -48 -16 -48 WIRE 128 -48 32 -48 WIRE 192 -48 128 -48 WIRE -80 -32 -112 -32 WIRE 32 -16 32 -48 WIRE -112 0 -112 -32 WIRE -112 32 32 -16 WIRE 32 48 -112 0 WIRE -112 64 -112 32 WIRE -80 64 -112 64 WIRE 224 64 80 64 WIRE 32 80 32 48 WIRE 32 80 -16 80 WIRE 336 80 288 80 WIRE 128 112 128 -48 WIRE -80 128 -224 128 WIRE 224 128 192 128 WIRE 336 128 336 80 WIRE 336 128 304 128 WIRE -224 176 -224 128 WIRE 80 176 80 64 WIRE 80 176 -224 176 WIRE 128 176 80 176 WIRE -224 224 -224 176 WIRE 304 240 304 208 WIRE 336 240 336 192 WIRE 336 240 304 240 WIRE 368 240 368 -160 WIRE 368 240 336 240 WIRE 304 304 -224 304 WIRE -224 400 -224 304 FLAG -224 400 0 FLAG 192 -48 Vout SYMBOL res 320 224 R180 WINDOW 0 -84 36 Left 0 WINDOW 3 32 3 Left 0 SYMATTR InstName R1 SYMATTR Value 10k SYMBOL cap 288 240 R0 WINDOW 0 53 14 Left 0 WINDOW 3 46 47 Left 0 SYMATTR InstName C1 SYMATTR Value 1e-6 SYMBOL Digital\\\\or -48 -128 R0 WINDOW 0 -23 10 Left 0 SYMATTR InstName A1 SYMATTR SpiceLine trise 1e-6 tfall 1e-6 vhigh 5v Td=8nS SYMBOL Digital\\\\or -48 160 M180 WINDOW 0 -30 14 Left 0 SYMATTR InstName A2 SYMATTR SpiceLine trise 1e-6 tfall 1e-6 vhigh 5v td=10nS SYMBOL voltage -224 208 R0 WINDOW 3 36 71 Left 0 WINDOW 0 38 41 Left 0 SYMATTR Value PULSE(0 5 0 1nS 1nS 1mS 20mS) SYMATTR InstName AnyDigitalSignal SYMBOL Digital\\\\or 160 208 M180 WINDOW 0 -30 14 Left 0 SYMATTR InstName A3 SYMATTR SpiceLine trise 1e-6 tfall 1e-6 vhigh 5v td=10nS SYMBOL diode 352 192 R180 WINDOW 0 -43 30 Left 0 WINDOW 3 -95 -21 Left 0 SYMATTR InstName D1 SYMATTR Value 1N914 SYMBOL Digital\\\\or 256 160 M180 WINDOW 0 -30 14 Left 0 SYMATTR InstName A4 SYMATTR SpiceLine trise 1e-6 tfall 1e-6 vhigh 5v td=10nS TEXT -200 368 Left 0 !.tran .1 uic TEXT -456 -104 Left 0 ;Pulse Extension Circuit TEXT 8 352 Left 0 ;Uses Quad NOR chip

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

On Sun, 15 Mar 2009 15:05:15 -0700, D from BC wrote:

Try this:

Version 4 SHEET 1 948 740 WIRE -928 -32 -960 -32 WIRE -464 -32 -928 -32 WIRE -352 16 -400 16 WIRE -464 32 -496 32 WIRE -352 48 -352 16 WIRE -496 64 -496 32 WIRE -496 96 -352 48 WIRE -352 112 -496 64 WIRE -496 128 -496 96 WIRE -464 128 -496 128 WIRE -352 144 -352 112 WIRE -352 144 -400 144 WIRE -352 160 -352 144 WIRE -288 160 -352 160 WIRE -464 192 -496 192 WIRE -352 208 -352 160 WIRE -928 320 -928 -32 WIRE -832 320 -928 320 WIRE -672 336 -768 336 WIRE -496 336 -496 192 WIRE -496 336 -608 336 WIRE -352 336 -352 288 WIRE -352 336 -496 336 WIRE -928 384 -928 320 WIRE -352 400 -352 336 WIRE -928 528 -928 464 WIRE -352 528 -352 464 WIRE -352 528 -928 528 WIRE -928 576 -928 528 FLAG -928 576 0 SYMBOL res -336 304 R180 WINDOW 0 36 76 Left 0 WINDOW 3 36 40 Left 0 SYMATTR InstName R2 SYMATTR Value 1e6 SYMBOL cap -368 400 R0 WINDOW 0 -38 31 Left 0 WINDOW 3 -56 56 Left 0 SYMATTR InstName C2 SYMATTR Value 1e-6 SYMBOL Digital\\\\or -432 -64 R0 WINDOW 0 -30 7 Left 0 SYMATTR InstName A4 SYMATTR SpiceLine trise 1e-6 tfall 1e-6 vhigh 5v SYMBOL Digital\\\\or -432 224 M180 WINDOW 0 -30 14 Left 0 SYMATTR InstName A5 SYMATTR SpiceLine trise 1e-6 tfall 1e-6 vhigh 5v SYMBOL voltage -928 368 R0 WINDOW 3 24 104 Invisible 0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR Value PULSE(0 5 .1 1e-6 1e-6 1E-3 .5 3) SYMATTR InstName V2 SYMBOL Digital\\\\or -800 256 R0 WINDOW 0 -30 7 Left 0 SYMATTR InstName A3 SYMATTR SpiceLine trise 1e-6 tfall 1e-6 vhigh 5v SYMBOL diode -608 320 R90 WINDOW 0 0 32 VBottom 0 WINDOW 3 32 32 VTop 0 SYMATTR InstName D1 SYMATTR Value 1N4148 TEXT -912 552 Left 0 !.tran 5 uic TEXT -280 160 Left 0 ;OUT TEXT -1000 -32 Left 0 ;IN

JF

Yup..that works.. Neato! :)

Thanks

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

Since you want the output to remain high as long as the input is high, one might conclude that one needs a retriggerable one-shot. However, most one-shots are triggered on an edge, so that is out. What might do the job is a gae combined with a one-shot that triggers on the input fall (down-going) edge; OR the input with that oneshot output. Or....maybe use a modified one-transistor one-shot... ..input keeps the transistor ON and a RC on the base keeps it on for a (short) period afterwards.