Long time delay

Hello,

I'm not sure if this is the correct place to post this query but I am hoping someone may be able to help.

I am looking for an accurate way to create a 'one-shot' delay adjustable between 30 - 45 minutes.

People have suggested using a PIC. Is this easy to implement? Are there dedicated I.C's that will accurately do the job?

Thanks.

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M.Joshi
Reply to
M.Joshi
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You certainly could do it with a PIC, AVR or any other microcontroller, which I would suggest if you're already proficient using them. An easier solution would probably be something like the 74HC4060 IC which contains an onboard oscillator and a ripple counter, they're often used to get long delays. If you go to

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you can look it up and see the datasheet and you can even get a few free samples of the SN74HC4060NE4 they offer if you'd like to play around with one.

Reply to
James Sweet

A 555 connected for monostable start on power up will do this. Do a google on NE555 to find a site with the spec sheet which will give details of how.

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*I'd kill for a Nobel Peace Prize *

    Dave Plowman        dave@davenoise.co.uk           London SW
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Reply to
Dave Plowman (News)

A 555 is good for delays of a few seconds to a few minutes, but to get a 45 minute delay will require a huge timing capacitor and the time delay won't be very accurate at all. You really need to use a counter to scale down a higher frequency for such long delays.

Reply to
James Sweet

You can also buy digitally set time delay relays which you can program by little switches on their tops. These cost $50-70, give you a DPDT contact set and can be set to delay anywhere from seconds to hours.

Google on "time delay relay"

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----------------------------------------------- Jim Adney snipped-for-privacy@vwtype3.org Madison, WI 53711 USA

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Reply to
Jim Adney

This is not strictly speaking, a problem - if you use the CMOS version of the 555, from Harris, for instance. This is capable of producing delays from " microseconds to hours ", quoting from the Maplin data, for instance. The only reason that the bipolar 555 had trouble with large values of caps, was the typical leakage of these exceeding the trigger / threshold pins' input currents, when large value timing resistors were used to go with the large value caps. This limited you to a meg or so and a few tens of microfarads if you wanted a stable predictable timer. This is not the case with the CMOS version, where the input currents are in pico amps, so you can use large value resistors and caps to get much longer delays. In terms of sheer simplicity, I'm with Dave on this one, although your clock and divider solution is an elegant way of achieving the same result, and one that I've used in the past ;-)

Arfa

Reply to
Arfa Daily

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Another problem with long time delays is how to calibrate the delay. If you do use the 555 or similar version then it could take a week to set the time. Remember it is 30 minuits between checks. The beter way is to use some kind of devider chain so you can set the timer up. He may want to use the 555 and a 100:1 devider. I have not checked to see what is out on the market now but there should be lots of chips that will devide by almost anything. Probably running an oscillator very fast and deviding it down will be more accurate and maybe easier to set. If the device is operated off AC then deviding the 60 hz will be a good place to start.

Reply to
Ralph Mowery

Provided you use a good quality low leakage cap, and high stability high value resistors, the delay time should be predictable with reasonable accuracy, using the standard 555 timing formula. Shouldn't take more than 3 or 4 runs to get the time delay down to what you need within a few seconds. It seemed to me that the OP needed a 'simple' solution, which the 555 circuit is, requiring only one resistor and one capacitor besides the device itself ( the CMOS version doesn't need either the supply decoupling against crowbarring, or the control pin decoupling ).

This is in contrast to the clock and divider solution, which I accept is totally predictable, but requires a divide ratio of 162000 ie 18 bits to arrive at 45 minutes,even using a low speed clock such as the 60Hz line supply ( which will also need clamping and shaping to form a suitable clock ). Also, some ANDing will need doing on the output of the divider to get an output at the required time delay. Not as simple as the timer chip solution, properly implemented.

Arfa

Reply to
Arfa Daily

You're right of course. I wonder if the U6047 is still available. It was designed for things like car heated rear window timing and can be set from a few seconds to many hours with standard components - and drive a 20 amp relay coil directly with a 12 volt rail. It also gives a choice of simple triggering methods. Luckily, I've got a small stock.

If there's a modern equivalent I'd be pleased to know of it.

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*There are two sides to every divorce: Yours and shit head's*

    Dave Plowman        dave@davenoise.co.uk           London SW
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Dave Plowman (News)

There's lots of similar chips out there, you reminded me too that yet another possible solution would be to use a car window defroster timer, many are built right into the buttons and can be had for a few bucks at a U-pull yard.

Reply to
James Sweet

Thanks for your reply guys.

I think the 555 I.C solution may be the simplest. I have some NE555's

- I believe they are the CMOS type?

Is the formula T = 1.14*R*C

Does the output sink high/low during the timing period?

Can the output signal be used to drive another I.C?

Thanks.

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M.Joshi
Reply to
M.Joshi

IIRC, NE555 aren't CMOS. Look for something like the ICM7555. And apart from allowing much longer timing intervals, the quiescent current is tiny.

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*I'm not being rude. You're just insignificant 

    Dave Plowman        dave@davenoise.co.uk           London SW
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Reply to
Dave Plowman (News)

Agreed. NE555 is the normal bipolar version of the IC. As Dave says ICM7555 is a CMOS

Arfa

Reply to
Arfa Daily

"Arfa Daily" bravely wrote to "All" (05 Sep 05 12:53:28) --- on the heady topic of "Re: Long time delay"

AD> From: "Arfa Daily" AD> Xref: core-easynews sci.electronics.repair:341392

AD> Provided you use a good quality low leakage cap, and high stability AD> high value resistors, the delay time should be predictable with AD> reasonable accuracy, using the standard 555 timing formula. Shouldn't AD> take more than 3 or 4 runs to get the time delay down to what you need AD> within a few seconds. It seemed to me that the OP needed a 'simple' AD> solution, which the 555 circuit is, requiring only one resistor and AD> one capacitor besides the device itself ( the CMOS version doesn't AD> need either the supply decoupling against crowbarring, or the control AD> pin decoupling ). AD> This is in contrast to the clock and divider solution, which I accept AD> is totally predictable, but requires a divide ratio of 162000 ie 18 AD> bits to arrive at 45 minutes,even using a low speed clock such as the AD> 60Hz line supply ( which will also need clamping and shaping to form a AD> suitable clock ). Also, some ANDing will need doing on the output of AD> the divider to get an output at the required time delay. Not as simple AD> as the timer chip solution, properly implemented.

AD> Arfa

The cmos version of the "555" timer is the "7555" and an excellent choice for stable delays. I've used one to get a very stable 42 minutes delay using a poly cap and high value resistor for the timing elements. Only problem with the "7555" is the output can't drive as much current.

The 4060 is a nice binary divider chain with 14 stages but it isn't the only one. The 4045 has 21 stages for example. However, the nicer device is the 4536 which has 24 stages and is programmable. In one mode is accepts BCD inputs to control 14 stages. For example, this goes nicely with decade trimmer switches which output BCD directly.

A*s*i*m*o*v

... That was a fascinating period of time for electronics

Reply to
Asimov

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