reynhout@wpi.wpi.edu (Andrew Reynhout) (09/29/89)
Help! This is an amusingly simple question, but I've been working on it for some time now, and can't come up with an answer... I need a circuit that will, on application of power, cause a delay of 5-20 seconds before allowing current to flow through (a different part of the circuit) Basically, it should take, say, 12v, wait 10 seconds, then trip a relay. It's for an alarm circuit. (I didn't see much point in paying $159 for $30 of components and a few hours of work.) I tried a deceptively complex setup with a FET and a timing cap and all sorts of other nasty things, but I can't get ANYTHING out of it. Any help would be greatly appreciated... Andrew
arnief@tekgvs.LABS.TEK.COM (Arnie Frisch) (09/30/89)
To build a reproducible time delay of several seconds to a minute - or more - a good approach is to do it digitally using CMOS. Build an inverter based oscillator out of two resistors a capacitor and two inverter sections (any good CMOS application manual will show how). Follow this with a multi-stage counter. The counter will have to be reset at power on - This will take a diode, a capacitor and a resistor. Limiting yourself to 1 uf capacitors and 1 meg resistors and using a seven stage counter IC, you should be able to get delays up to 300 seconds. I don't do schematics for free! Arnold Frisch Tektronix Laboratories
jans@tekgvs.LABS.TEK.COM (Jan Steinman) (09/30/89)
<I need a circuit that will, on application of power, cause a delay of 5-20 seconds before allowing current to flow through. Basically, it should take, say, 12v, wait 10 seconds, then trip a relay...> Check out the CMOS 4528 dual mono. These suckers will delay up to *days* with careful parts selection. (your basic 10 Gohm resistor: clean a piece of glass with MEK, draw a thin line of india ink on it... the leads are a problem :-) They're re-triggerable, and lack a lot of the nasty behavior of the infamous 555. Plus, you get two of them in a DIP. For a 10 second delay, try 10 Mohm and 1 uf. Capacitor leakage current will reduce the effective time constant -- use non-electrolytic caps with resistors over half a meg or so. Jan Steinman - N7JDB Electronic Systems Laboratory Box 500, MS 50-370, Beaverton, OR 97077 (w)503/627-5881 (h)503/657-7703
larry@kitty.UUCP (Larry Lippman) (09/30/89)
In article <4377@wpi.wpi.edu>, reynhout@wpi.wpi.edu (Andrew Reynhout) writes: > I need a circuit that will, on application of power, cause a delay of 5-20 > seconds before allowing current to flow (a different part of the circuit) > Basically, it should take, say, 12v, wait 10 seconds, then trip a relay. > It's for an alarm circuit. (I didn't see much point in paying $159 for $30 of > components and a few hours of work.) > I tried a deceptively complex setup with a FET and timing cap and all sorts > of other nasty things, but I can't get ANYTHING out of it. I am assumning that this is NOT for an OEM application where you must have this circuit function on a PC board along with other circuit elements. All you need is a time delay relay, with a delay-on-operate mode. The simplest time delay relay is of the thermal delay type, as manufactured by Amperite or GV Controls. You can often find such thermal delay relays (which are usually made for octal sockets, although 7/9-pin miniature also exists) in surplus stores for a buck or so. A far better approach is to use a solid-state timer, which can be purchased new for as little as $ 25.00, and surplus for $ 5.00 or less. Such a solid-state timer - which is available in many package types - will do EXACTLY what you want and will provide an isolated set of relay contacts. <> Larry Lippman @ Recognition Research Corp. - Uniquex Corp. - Viatran Corp. <> UUCP {allegra|boulder|decvax|rutgers|watmath}!sunybcs!kitty!larry <> TEL 716/688-1231 | 716/773-1700 {hplabs|utzoo|uunet}!/ \uniquex!larry <> FAX 716/741-9635 | 716/773-2488 "Have you hugged your cat today?"
morris@jade.jpl.nasa.gov (Mike Morris) (09/30/89)
In article <4377@wpi.wpi.edu> reynhout@wpi.wpi.edu (Andrew Reynhout) writes: > > Help! This is an amusingly simple question, but I've been working on it >for some time now, and can't come up with an answer... > > I need a circuit that will, on application of power, cause a delay of 5-20 >seconds before allowing current to flow through (a different part of the circuit) > Basically, it should take, say, 12v, wait 10 seconds, then trip a relay. >It's for an alarm circuit. (I didn't see much point in paying $159 for $30 of >components and a few hours of work.) > I tried a deceptively complex setup with a FET and a timing cap and all sorts >of other nasty things, but I can't get ANYTHING out of it. Look in a catalog for an Amperite Delay Relay. They come in the same package as the thermeonic high-voltage-depletion-mode-JFETs (a.k.a. Vacuum Tubes), and are just a heater and a pair of bimetalic contacts. They come in 6v, 12v, 24v, 110v and 220v, and in times ffrom 1 second to 3 minutes, normally open ort normally closed. the part number format is obvious: <voltage><contact style><time in seconds> 6NO180= 6v NO 3 minute 12NC1 12v NC 1 second 110C30 110v NV 30 second Note that the heater can take DC or AC, it doesn't care. I've seen both octal format and 9-pin-miniature versions. At the surplus store they are in the $1 region. I saw them new in a Newark catalog a couple of years ago. Mike Morris UUCP: Morris@Jade.JPL.NASA.gov ICBM: 34.12 N, 118.02 W #Include quote.cute.standard PSTN: 818-447-7052 #Include disclaimer.standard cat flames.all > /dev/null
gbell@pnet12.cts.com (Greg Bell) (10/02/89)
jans@tekgvs.LABS.TEK.COM (Jan Steinman) writes: >They're re-triggerable, and lack a lot of the nasty behavior of the infamous >555. Plus, you get two of them in a DIP. For a 10 second delay, try 10 Mohm Speaking of the nasty behavior of the 555, is there any way to "desensitize" the trigger input so that it doesn't trigger when you turn on a flourescent light? (or a TV, or ...) The problem is that the 555 is fast... ie. it reacts to extremely brief negative going spikes on the trigger line, right? I've tried slowing the thing down with bypass caps, but it never helps much... Greg Bell_________________________________________________________ Hardware hacker | Electronics hobbyist | UUCP: uunet!serene!pnet12!gbell EE major at UC San Diego |