Looking for a Low Cost On Delay Timer

On Tue, 20 Aug 2013 14:12:28 -0700, "Guv Bob" wrote:

--- For way under $20, this'll work, and if you need NC contacts, all you'll have to do is put either a solid state relay or a mechanical relay with a catch diode across the LED.

Version 4 SHEET 1 880 680 WIRE 0 -48 -128 -48 WIRE 160 -48 0 -48 WIRE 256 -48 160 -48 WIRE 352 -48 256 -48 WIRE 400 -48 352 -48 WIRE 528 -48 480 -48 WIRE 528 -16 528 -48 WIRE 0 0 0 -48 WIRE 160 0 160 -48 WIRE 352 0 352 -48 WIRE 528 80 528 48 WIRE 256 96 256 -48 WIRE 0 112 0 80 WIRE 224 112 0 112 WIRE -128 128 -128 -48 WIRE -96 128 -128 128 WIRE 0 128 0 112 WIRE 0 128 -32 128 WIRE 352 128 352 80 WIRE 352 128 288 128 WIRE 464 128 352 128 WIRE 160 144 160 80 WIRE 224 144 160 144 WIRE -128 176 -128 128 WIRE 0 176 0 128 WIRE 160 176 160 144 WIRE 528 256 528 176 WIRE -128 288 -128 256 WIRE 0 288 0 240 WIRE 0 288 -128 288 WIRE 160 288 160 256 WIRE 160 288 0 288 WIRE 256 288 256 160 WIRE 256 288 160 288 WIRE -128 320 -128 288 FLAG 528 256 0 FLAG -128 320 0 SYMBOL Comparators\\LT1017 256 128 R0 WINDOW 0 27 24 Left 2 WINDOW 3 12 52 Left 2 SYMATTR InstName U1 SYMBOL npn 464 80 R0 SYMATTR InstName Q1 SYMATTR Value 2N3904 SYMBOL res 336 -16 R0 SYMATTR InstName R1 SYMATTR Value 10k SYMBOL res 496 -64 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R2 SYMATTR Value 680 SYMBOL LED 512 -16 R0 SYMATTR InstName D3 SYMATTR Value NSCW100 SYMBOL res 144 -16 R0 SYMATTR InstName R3 SYMATTR Value 100k SYMBOL res 144 160 R0 SYMATTR InstName R4 SYMATTR Value 150k SYMBOL cap -16 176 R0 SYMATTR InstName C1 SYMATTR Value 0.47µ SYMBOL res -16 -16 R0 SYMATTR InstName R5 SYMATTR Value 10meg SYMBOL voltage -128 160 R0 WINDOW 3 24 96 Invisible 2 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V1 SYMATTR Value PULSE(0 12 1 10ms 10ms 5s 10s) SYMBOL diode -32 112 R90 WINDOW 0 -38 31 VBottom 2 WINDOW 3 -33 37 VTop 2 SYMATTR InstName D2 SYMATTR Value 1N4148 TEXT -162 344 Left 2 !.tran 20 startup

-- JF

seconds. Then output will go back off and stay off until the input goes to zero. Then cycle starts again.

with NC contacts. Tons of stuff $100+, but for this application, it has to be under $20.

Thanks John, I'm not following you. Can you sketch the circuit?

seconds. Then output will go back off and stay off until the input goes to zero. Then cycle starts again.

one with NC contacts. Tons of stuff $100+, but for this application, it has to be under $20.

Thanks again! Would this work?

NTE955M Timer, (555 Type), 200 mA Iout, CMOS 8 DIP 1.20

seconds. Then output will go back off and stay off until the input goes to zero. Then cycle starts again.

finding one with NC contacts. Tons of stuff $100+, but for this application, it has to be under $20.

mechanical

Vcc)

I was going to say this sounded like a perfect fit for a 555 timer. (So what's the best RC combo to get 5 seconds from a 555?)

George H.

I used to know all that stuff by heart, but I've been swapping modules too long. This not the usual rush job, so it's a nice change to be able to spend some time on it. Now I'm off to re-learn all the RC stuff.

Maybe like this:

in------+-------------+ | | | . . . .|. . . . | . VCC(8) . | . . +-----+-------RES(4) OUT(3)------ out _|_ | . 555 . D1 A [R1] +---TH(6) DIS(7)-- 'T` | | . . +-----+---+---TR(2) CV(5)-- | . . C1 ===== . GND(1) . | . . . .|. . . . | | ----+-------------+--- ground U1 LMC555 / 7555 D1 1N914 C1 10uF R1 470K

modules too long. This not the usual rush job, so it's a nice change to be able to spend some time on it. Now I'm off to re-learn all the RC stuff.

That was my 2nd guess. LOL!

In industrial relay timer parlance, we'd call that an "interval timer". An "off delay" timer would drop out a period of time after the power was removed (a more rare beast since it would have two power supplies or a big capacitor inside). An interval timer is/was just an on delay timer with logic inversion before the relay driver, so it pulled in immediately upon connection to the power source and drops out after the delay.

The terms are used differently in different domains so I wouldn't count on them being valid in any particular instance. For example, some cretinous poltroons will refer to a recycle timer as an "interval timer".

Best regards, Spehro Pefhany

These used to be called "Delay Relays" and looked like a vacuum tube. Now there are solid state models. See .

You can find these on eBay, i.e.

You should be able to figure out a way to get what you need though you may need another regular relay as a latch.

Well under $20.

Yes that is the way I would do it I have done many many projects using a

Simple just use the Reset Pin..

When 12VDC is applied to the input, I need a 12VDC output for 5 seconds. Then output will go back off and stay off until the input goes to zero. Then cycle starts again.

Current for both legs is in the 10-50ma range.

A simple on-delay timer would work but I'm having trouble finding one with NC contacts. Tons of stuff $100+, but for this application, it has to be under $20.

===

Thanks for all the tips and good info. I had wanted to put something together from components but my brain is too far behind these days. I'm going to give this a shot and hopefully I'm not picking the wrong one. It's $5 at Frys...

Velleman MK111

On a sunny day (Sun, 25 Aug 2013 23:29:54 -0700) it happened "Guv Bob" wrote in :

The reason I did not reply with a ciruit or whatever is that your logic is false.

You say: 'until', that means the output goes active again. Then you say : 'cycle starts again', but that cycle is not the same now (starts active).

First, for yourself, work out the correct logic. Then you already have the solution, probably from stuff you have laying about.

It can be modified to do what you say you want.

seconds. Then output will go back off and stay off until the input goes to zero. Then cycle starts again.

with NC contacts. Tons of stuff $100+, but for this application, it has to be under $20.

together from components but my brain is too far behind these days. I'm going to give this a shot and hopefully I'm not picking the wrong one. It's $5 at Frys...

Hmmmm....... in that case, forget the electronics! ;O)

seconds. Then output will go back off and stay off until the input goes to zero. Then cycle starts again.

with NC contacts. Tons of stuff $100+, but for this application, it has to be under $20.

together from components but my brain is too far behind these days. I'm going to give this a shot and hopefully I'm not picking the wrong one. It's $5 at Frys...

- Hmmmm....... in that case, forget the electronics! ;O)

If I disconnect pin 7, would that make it a one-shot pulse?

On a sunny day (Thu, 29 Aug 2013 10:18:17 -0700) it happened "Guv Bob" wrote in :

When power is off C1 is discharged. When power comes on the gate of MOSFET T1 is posive via C1, and C1 slowly charges via R1, R.C time, select a suitable capacitor and resistor. The gate voltage slowly drops, and then T1 stops conducting. When power goes off, then C1 is discharged again via D1.

D2 and C2 are needed to prevent transients on the drain (load line) of T1 piercing the gate electrode isolation layer.

IRLZ34 is a logic level (2 to 3 V gate on IIRC) MOSFET.

Alternative solution: