Names can be confusing, so here's what I'm doing....
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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 guys. Grainger has it for $30. Before I head up there... this is not something that has to be done right away... would putting together a circuit with this work?
A transistor /amplifier Ic, plus a capacitor, and a few resistors should do it. What time scales you you need? How fast does it need to switch on and switch off? What voltage tolerance do you need? -- ie if it is 11V out is that OK? What supply voltage do you have? Can the input drop to zero before 5 sec and what behaviour do you expect in that case? How accurate must the 5 sec be? etc
this is not something that has to be done right away... would putting together a circuit with this work?
Hey unruh!
Initially input voltage is zero. When input goes to 12VDC, output should energize immediately to 12VDC, stay eneregized for 4-6 seconds, then drop to zero again. When input goes to zero, output stays off until starts over.
Within 1/2 second is fine.
Yes, 9-13 out is fine. Supply is typically 11-12VDC.
expect in that case? Yes it can. Output should go on when input first goes on, then output should go off any time input is disconnected.
Immediately does not mean anything. on a time of 5 sec?1 sec 1 millisecond? 10^-100 sec? If you are looking at relays, they are of order 1/10 sec. Is that good enough?
OK.
So a simple rc circuit opamp should be fine.
The input goes through a resistor divider to the + input of an opamp, the input also goes through a resistor (with a parallel reverse diode)) to a capacitor to ground, and the junction of reistor and capacitor goes to the - input of the opamp. When input goes up, the output of the opamp will peg out positively, until the capacitor charges up sufficiently at which point the ouput will go to zero the resistor/capacitor is chosen so that this is 5 sec. If the output goes to 0, the capacitor is discharged by the divider and the output stays at 0. If the resistor bridge low enough (say 1K ohm) and the risistor/capacitor high enough (eg R=100K C= 2uF) -- I have not checked these values -- they are at best orders of magnitude-- you would not need the diode.
You could run a very high resistor from the cap to the positive rail as well, to make sure that when the input is low, the capacitor remains slightly charged, and the opamp is driven to low output.
Total cost ? < $1 Output current-- only limited by the opamp output current which could be thousands of amps with suitable(very expensive) ouput transistors. (for cheap opamps hundreds of mA.)
relays? why? His current demands are 10s of mA. That the opamp can handle by itself. Cost? $1 vs $30? While the former may not matter to you or to most as a oneoff, if he has to build 100000 of them, it can be significant. We have no idea what he wants this for.
He has not told us what he is doing. You are perfectly correct if a) it is one off, b) it is a job, and c) he can actually get them in a reasonable time. Remember it can take 10s of sheets of paperwork, 5 signatures and 2 week wait time sometimes to get one object. Whipping up a little circuit with spare parts can be done in 10 min.
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...
Except that looks like an oscillator rather than a "oneshot" You said that you wanted something that if the input was larger than 5 sec, the output would go high for 5 sec, and then drop to 0. If the input droped before 5 sec was up, you wanted the output to drop as well. Then you wanted it to wait until the input went high again before doing that again. This device has a relay (why would you need a relay for 50ma? Most ICs can handle an ouput current of 50mA at 12V without the need of a relay.
This kit is an oscillator, where you can adjust the time it is on and the time it is off with the pots. It has no input.
It uses a 555 timer chip. The primary design of the 555 is to initiate a pulse when the input goes high, and stays high for the requsite time even if the input drops again. If the input stays high beyond the time Ie, I think you want to think your way through what you need carefully.
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.
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...
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carefully.
Thanks, yes you're right. What value resistor could I substitute for RV1 to give a pause time between pulse to 10 minutes?
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.
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...
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carefully.
- Thanks, yes you're right. What value resistor could I substitute for RV1 to give a pause time between pulse to 10 minutes?
PS -- This will actually give me another option I can use instead of just the one-shot.
RC=t roughly. (depends on exactlywhee in the charge/discharge cycle the thing triggers). But R probably should not be much over 1Mohm, as otherwise the input resistance of the ic becomes important. Then C should be about 600uF (probably not electrolytic as the internal resistance can become important but finding anything else at that size is pretty impossible)
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.
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...
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for RV1 to give a pause time between pulse to 10 minutes?
Thanks. I think I'll put a fixed 2M ohm in series and see if I can get a 3-5 minute range.
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.
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...
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for RV1 to give a pause time between pulse to 10 minutes?
- Thanks. I think I'll put a fixed 2M ohm in series and see if I can get a 3-5 minute range.
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If I disconnect pin 7, would that make it a one-shot pulse?
2dnUVZ snipped-for-privacy@earthlink.com... > >> > Names can be confusing, so here's wh at I'm doing.... > >> >> > >> >>
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gif > >> >> > >> >> When 12VDC is applied to the input, I need a 12VDC outp ut 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 le gs is in the 10-50ma range. > >> >> > >> >> A simple on-delay timer would w ork 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 pu t something together from components but my brain is too far behind these d ays. I'm going to give this a shot and hopefully I'm not picking the wrong one. It's $5 at Frys... > >> > > >> > Velleman MK111 > >> >
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> >> > >> Except that looks like an oscillator rather than a "oneshot" > >> You said that yo u wanted something that if the input was larger than 5 > >> sec, the output would go high for 5 sec, and then drop to 0. If the > >> input droped befo re 5 sec was up, you wanted the output to drop as well. > >> Then you wante d it to wait until the input went high again before doing > >> that again.
even if the input drops again. If the input stays high beyond the time > >
Jeeeeeze, If you'd have bought the damn Altronix 6062 you'd have been up an d running in 15 minutes instead of EF-en around with this $5.00 piece of cr ap.
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