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One shots, timers, etc

I have a question about one-shots, multivibrators, and other like devices, if I may be permitted.

I am a somewhat familiar with a number of one-shots and timer such as the hc123 and hc4538 for short pulses, and timing, but I am in need of something that can give me a timeout pulse for up to five minutes. When I look at the data sheets for these devices, I am not sure where I need to check to learn if the device is stable enough for a pulse that long, and if a simple R/C network can accomplish what I am hoping to provide.

The question will be, how accurate? and I can only say that it must be as accurate as I can make it, and still make it affordable, so that is why I am wondering where on the datasheet I can find such information so I can understand my options.

Are these kinds of chips going to be the right approach, or is there another way I should be accomplishing this long of a timeout with some degree of accuracy?

I will need to select five timeouts, from one minute, through five minutes. I thought about using a dipswitch to choose between five different RC combinations. An idea for something more elegant would certainly be appreciated. Thanks for the space and the consideration.

John

Reply to
vanagonvw
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Reply to
not_keith

Hello John,

For such long intervals I would use a CD4060. That chip contains an oscillator and a 14-stage divider. You can even crystal-control it for really accurate timing. This will be much more reliable than messing around with microamps and some one-shot chip.

Regards, Joerg

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Reply to
Joerg

The problems comes with the bias currents into the inputs, the parallel resistors in capacitors and the temperature dependence of the capacitances. You can make your own delay generator by loading a capacitor. You have to take a low leakage cap, such as polypropylene. A big one, 10uF up. Then as comparator take a FET input opamp, with a leakage below 0.1pA. Then load this cap with few hundred MegaOhms from 5V or so.

Much simpler is a small CPU such as an AVR or a PIC.

Rene

--
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& commercial newsgroups - http://www.talkto.net
Reply to
Rene Tschaggelar

IIRR the classic bipolar 555 timer is not a good choice for long time intervals - the bias current on the input that senses the voltage across the capacitor is way too high.

There are CMOS versions of the 555 around which probably can be persuaded to give a 5 minute delay, but the worst case leakage current through the protection diodes may be too high to allow you to guarantee this.

A digital counter based approach is almost always cheaper, more reliable, and more compact. The Xilinx (formerly Philips) Coolrunner CMOS PLDs are probably the simplest single active device you can use to do the job, but a minimal single chip microprocessor is probably going to be cheaper.

------------- Bill Sloman, Nijmegen

Reply to
bill.sloman

========================================================== The 4060 suggested so far is a good starting point, but in order to come up with anything meaningful you should mention what you want the outputs to look like. =========================================================

Yep, you're right, I should have been more precise in my description.

I would like to use an external signal, to trigger a pulse that lasts for either one, two, three, four, or five minutes, depending on a previously configured switch selection. Just one pulse, of that preset length of time is all I need to have. Once the pulse has timed out, the output would reset back to the inactive state, waiting for another trigger to start it again. Nothing fancy, or multiple outputs that are retriggerable or anything. Just a pulse of the proper duration, and then wait for another trigger to do it again.

I am expecting that the ckt would have a reset, that I could control if I wanted to terminate the pulse.

I think the 4060 is the choice of most for a more stable, repeatable configuration. I agree that the one-shots I mentioned are probably not going to be able to do the job.

Thanks for pointing that out so I could make myself a bit more clear on what I need.

John

Reply to
vanagonvw

using

Fred,

I am much obliged for you to take the time to sketch that circuit out for me to see. Helps a lot, and once I figure the starting and stopping sequences, it looks like something I can use, and learn from, so please pat yourself on the back for me, I appreciate your time and efforts. :-)

Thanks,

John

Reply to
vanagonvw

snipped-for-privacy@gmail.com wrote:

The simplest would be a START/STOP 4060 clocking a 4017 and then using the DIP switch to select outputs 1 through 5 of the 4017. This implies that the 4060 produces the 4017 input clock at 60 second intervals. The

60 seconds is 1/2 the period of 4060 2^14 divide register making it 120 second=Tosc x 2^14 or 4060 oscillation frequency=7.3msec which is quite high. A cascade of two 4060's would make this 1.8usec which can be made very accurate- something like RC*2.2 nominally or a 220pF NPO and 5K adjustable pot set for 3.7K or so for the timing. The tricky part is getting the 4017 to clock off the positive and negative transitions of the 4060 output clock- and this is easily done with an EXOR. Then your control is simply to hold all the IC's in RESET, lift RESET to initiate timing, and terminate when selected 4017 goes high. Something like this, press START to initiate timing- use the MR signal as an output- and spare NAND if you want output HIGH during timing interval:

View in a fixed-width font such as Courier.

. .. . .. +-----------------------------------------+--------------------+ .. +-| \ 10K _ | | .. | | O--/\/\-+----| \ | | .. +-|__/ | | O----+ / | .. | +|__/ | 10K | .. | | | / | .. _ | +-------+ | \ | .. GND---o o------+ | | | | .. RESET +-------|-+---+ GND | .. | __ | | SELECTED -----> | .. +| \ | | OUTPUT | .. START | O--+ | MINUTES | .. GND--o o-+----------|__/ | (DIP SW ) | .. | | | .. VCC-/\/\-+ | | .. 10K +----------------+-------------------+ | .. | | | | .. NPO +------4060 +------4060 +------4017 | .. 220p | MR | | MR | | MR | | .. +--||--+CT | |CT | | | | .. | | Q12|--+ | Q14|--+ +--+CP Q1| | .. |5K pot| | | | | | | | Q2| | .. +-/\/\-+RT | | |RT | | | | Q3|>--+ .. | | | | | | | | | Q4| .. | 10K | | | | | | | | __ Q5| .. +-/\/\-|RS | +---|RS(phi1) | | | | CE | .. +---------+ +---------+ | | +---------+ .. | | | .. | | GND .. | | .. +-------------------+ | .. | | .. | | .. | | .. | .--------. | .. | |74HCT132| | .. | .--------. | .. +----------| \ | .. | | O-+ | .. | +-|__/ | | .. 10K | __ | | | .. +--/\/\---+-| \ | | __ | .. | | O--+ +-| \ | .. +---------+-|__/ | | O--+ .. | | | +-|__/ .. ===470p | | __ | .. | | +-| \ | .. GND | | O-+ .. +----------|__/ . .. .

Reply to
Fred Bloggs 

--
The analog timers like the '123, the '4538, and the 555 and its CMOS
versions will, in all likelihood, not give you the accuracy and
stability you need, the reason being that you will be at the mercy of
the variations in output times caused by the timing components and the
chips themselves.
---   

>I will need to select five timeouts, from one minute, through five
>minutes. I thought about using a dipswitch to choose between five
>different RC combinations. An idea for something more elegant would
>certainly be appreciated.
Reply to
John Fields

Fred Bloggs wrote:

I suppose you can eliminate a chip by doing this- 4 cheap chips and a DIP sw: View in a fixed-width font such as Courier.

. .. . .. .. +---------------------------------------------------------+----+ .. +-| \ 10K _ | | .. | | O--/\/\-+----| \ / | .. +-|__/ | | O----+ 10K | .. | +|__/ | / | .. | | | \ | .. _ | +-------+ | | | .. GND---o o------+ | | GND | .. RESET +-------|-+---+ | .. | __ | | SELECTED -----> | .. +| \ | | OUTPUT | .. START | O--+-----|--->OUT MINUTES | .. GND--o o-+----------|__/ | (DIP SW ) | .. | | | .. VCC-/\/\-+ | | .. 10K +----------------+-------------------+ | .. | | | | .. NPO +------4060 +------4060 +------4017 | .. 220p | MR | | MR | | MR | | .. +--||--+CT | |CT | | | | .. | | Q12|--+ | Q13|--+ +--+CP Q1| | .. |5K pot| | | | | | | | Q2| | .. +-/\/\-+RT | | |RT | | | | Q3|>--+ .. | | | | | | | | | Q4| .. | 10K | | | | | | | | __ Q5| .. +-/\/\-|RS | +---|RS(phi1) | | | | CE | .. +---------+ +---------+ | | +---------+ .. | | | .. | | GND .. | | .. +-------------------+ | .. | __ | .. +---+-| \ | .. | | O---------------+ .. +-|__/ . .. . .. .. 1-5 MINS .. OUT +------------------+ .. | | | | | | .. | | | | | | .. | | | | | | .. ----+ +------ . .. ^ .. | .. press .. start . ..

Reply to
Fred Bloggs

Fred Bloggs wrote:

View in a fixed-width font such as Courier.

. .. . .. .. +--------------------------------------+------------------+ .. +-| \ 10K _ | | .. | | O--/\/\-+----| \ / | .. +-|__/ | | O----+ 10K SELECTED | .. | +|__/ | / OUTPUT | .. | | | \ MINUTES | .. _ | +-------+ | | | .. GND---o o------+ | | VCC +-+-+-+-+ .. RESET +-------|-+---+ | | | | | .. | __ | | +-+-+-+-+- .. +| \ | | |o o o o o | .. START | O--+-----|--->OUT DIP SW |/ / / / / | .. GND--o o-+----------|__/ | |o o o o o | .. | | ---------- .. VCC-/\/\-+ | \ \ \ \ \ .. 10K +----------------+------------------+ -------+ .. | | | | .. NPO +------4060 +------4060 +------4017 | .. 220p | MR | | MR | | MR | | .. +--||--+CT | |CT | __ | | / .. | | Q12|--+ | Q13|--+-| \ | Q1| |5 .. |5K pot| | | | | | | O--+CP Q2| | .. +-/\/\-+RT | | |RT | +-|__/ | Q3|>--+ .. | | | | | | | Q4| .. | 10K | | | | | | __ Q5| .. +-/\/\-|RS | +---|RS(phi1) | | CE | .. +---------+ +---------+ +---------+ .. | .. GND . .. . .. 1-5 MINS .. OUT +------------------+ .. | | | | | | .. | | | | | | .. | | | | | | .. ----+ +------ . .. ^ .. | .. press .. start . ..

Reply to
Fred Bloggs

View in a fixed-width font such as Courier.

. .. . .. .. +--------------------------------------+------------------+ .. +-| \ 10K _ | | .. | | O--/\/\-+----| \ / | .. +-|__/ | | O----+ 10K SELECTED | .. | +|__/ | / OUTPUT | .. | | | \ MINUTES | .. _ | +-------+ | | | .. GND---o o------+ | | VCC +-+-+-+-+ .. RESET +-------|-+---+ | | | | | .. | __ | | +-+-+-+-+- .. +| \ | | |o o o o o | .. START | O--+-----|--->OUT DIP SW |/ / / / / | .. GND--o o-+----------|__/ | |o o o o o | .. | | ---------- .. VCC-/\/\-+ | \ \ \ \ \ .. 10K +----------------+------------------+ -------+ .. | | | | .. NPO +------4060 +------4060 +------4017 | .. 220p | MR | | MR | | MR | | .. +--||--+CT | |CT | __ | | / .. | | Q12|--+ | Q13|--+-| \ | Q1| |5 .. |5K pot| | | | | | | O--+CP Q2| | .. +-/\/\-+RT | | |RT | +-|__/ | Q3|>--+ .. | | | | | | | Q4| .. | 10K | | | | | | __ Q5| .. +-/\/\-|RS | +---|RS(phi1) | | CE | .. +---------+ +---------+ +---------+ .. | .. GND . .. . .. 1-5 MINS .. OUT +-------------------+ .. | | | | | | .. | | | | | | .. | | | | | | .. ----+ +------ . .. ^ .. | .. press .. start . ..

Reply to
Fred Bloggs

Naaah! Use a timer running at a reasonable speed where leakage can't get you, then divide down to the timing you want.

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.
Reply to
Jim Thompson

Use a PIC.

--
  Keith
Reply to
Keith Williams

I'm afraid I'm going against the tide here. Unlike the professionals, I think a 555 circuit with a 5-way rotary switch sounds fine!

You haven't been explicit about the accuracy, but the 555 itself is capable of 1%. With a low-leakage electrolytic as timing capacitor, and reasonably careful construction, you could expect close to that in practice. Here's a circuit to do what you specified:

formatting link 

--
Terry Pinnell
Hobbyist, West Sussex, UK
Reply to
Terry Pinnell

I am going to amend that circuit to improve the margin against race on the reset latch, clocking the 4017 through its CLOCK ENABLE /CE input, which is a negative active edge, and this frees the NAND inverter to drive the MASTER RESET MR of the counters and provide a 3:1 Tpd margin on the NAND latch hold time.

View in a fixed-width font such as Courier.

. .. . .. +--------------------------------------+------------------+ .. | __ | | .. +-| \ 10K _ | | .. | | O--/\/\-+----| \ / | .. +-|__/ | | O----+ 10K SELECTED | .. | +-|__/ | / OUTPUT | .. | | | \ MINUTES | .. _ | +--------+ | | | .. GND---o o------+ | | VCC +-+-+-+-+ .. RESET +--------|-+ | | | | | .. | __ | +-+-+-+-+- .. +-| \ | |o o o o o | .. _ | O--+--------->OUT DIP SW |/ / / / / | .. GND--o o-+----------|__/ | __ |o o o o o | .. START| +-| \ ---------- .. | | O------------+ \ \ \ \ \ .. VCC-/\/\-+ VCC--|__/ | -------- .. 10K | | .. +-----------------------------+ | .. | | | .. NPO +------4060 +------4060 +------4017 | .. 220p | MR | | MR | | MR | | .. +--||--+CT | |CT | |__ | /5 .. | | Q12|--+ | Q13|-----|CE Q1| | .. |5K pot| | | | | | Q2| | .. +-/\/\-+RT | | |RT | | Q3|>-+ .. | | | | | | | Q4| .. | 10K | | | | | | Q5| .. +-/\/\-|RS | +---|RS(phi1) | | CP | .. +---------+ +---------+ +---------+ .. | .. VCC . .. 1-5 MINS .. OUT +-------------------+ .. | | | | | | .. | | | | | | .. | | | | | | .. ----+ +------ . .. ^ .. | .. press .. start . ..

Reply to
Fred Bloggs

Fred Bloggs wrote:

....dropped an MR connection in the editing...

View in a fixed-width font such as Courier.

. .. . .. +--------------------------------------+------------------+ .. | __ | | .. +-| \ 10K _ | | .. | | O--/\/\-+----| \ / | .. +-|__/ | | O----+ 10K SELECTED | .. | +-|__/ | / OUTPUT | .. | | | \ MINUTES | .. _ | +--------+ | | | .. GND---o o------+ | | VCC +-+-+-+-+ .. RESET +--------|-+ | | | | | .. | __ | +-+-+-+-+- .. +-| \ | |o o o o o | .. _ | O--+--------->OUT DIP SW |/ / / / / | .. GND--o o-+----------|__/ | __ |o o o o o | .. START| +-| \ ---------- .. | | O------------+ \ \ \ \ \ .. VCC-/\/\-+ VCC--|__/ | -------- .. 10K | | .. +----------------+------------+ | .. | | | | .. NPO +------4060 +------4060 +------4017 | .. 220p | MR | | MR | | MR | | .. +--||--+CT | |CT | |__ | /5 .. | | Q12|--+ | Q13|-----|CE Q1| | .. |5K pot| | | | | | Q2| | .. +-/\/\-+RT | | |RT | | Q3|>-+ .. | | | | | | | Q4| .. | 10K | | | | | | Q5| .. +-/\/\-|RS | +---|RS(phi1) | | CP | .. +---------+ +---------+ +---------+ .. | .. VCC . .. 1-5 MINS .. OUT +-------------------+ .. | | | | | | .. | | | | | | .. | | | | | | .. ----+ +------ . .. ^ .. | .. press .. start . ..

Reply to
Fred Bloggs

You should be able to use a single pot on the CTL threshold setting:

View in a fixed-width font such as Courier.

V+ | +------------+-----------+---+---+---+----+ | | | | | | | | | | | | | | | | | | | | | | | +-------------------+ | +-----+-----+ |o o o o o | | | | | / / / / /| | | | |o o o o o | | | | +-------------------+ / | | | | | | | \ | | [R] [R] [R] [R] [R] /

Reply to
Fred Bloggs

Hmm- maybe this would work better:

View in a fixed-width font such as Courier.

V+ | +------------+-----------+---+---+---+---+---+ | | | | | | | | | | | | | | | | | | | | | | | +------------------+ | +-----+-----+ |o o o o o | | | | | / / / / /| | | | |o o o o o | | | | |1 2 3 4 5 | mins / | | +------------------+ \ | | | | | | | /

Reply to
Fred Bloggs

I suppose you could attempt a first order cancellation of CT leakage current, due to Rleak (also cancels bias currents), like so. The timeout is still KxNxRxCT, where K is adjusted with CTL pot, and N is number of MIN SEL resistor, obviously KxRxCT=60 seconds:

View in a fixed-width font such as Courier.

Reply to
Fred Bloggs

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