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I want to build a monostable circuit (a circuit with one input as a pushbutton), that will output logic '1' when the pushbutton is pressed for one hour (with the least error possible) then go back to its original state of outputting logic '0' until the pushbutton is pressed again.

I know about the 555 timer, but I also know that it does not behave good with very high time periods like one hour, some have suggested using a TLC555 which is a CMOS version, but I am not sure if this is going to work.

What I found on the internet are circuits using 4060 with an astable 555 timer, if you could suggest a way to convert this into a monostable circuit I would really appreciate it, if not please suggest another circuit.

I prefer suggestions with discrete hardware components over the microcontroller suggestions in general, but if it is the most suitable solution, please share with me.

Thank you all in advance.

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    \$\begingroup\$ I would go with an arduino. You won't get anything accurate without a microcontroller. \$\endgroup\$ Mar 29, 2021 at 14:44
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    \$\begingroup\$ A 555, two 16-bit counters (eg: SN74LV8154) daisy-chained and configured as a clock divider, and an SR latch to make it into a one-shot would do it. \$\endgroup\$ Mar 29, 2021 at 14:48
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    \$\begingroup\$ Looks like these guys have the job done for you: adafruit.com/product/3573 \$\endgroup\$
    – Eugene Sh.
    Mar 29, 2021 at 14:49
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    \$\begingroup\$ "... with the least error possible ..." isn't a proper specification unless you're prepared to pay for an atomic clock or use GPS for your timing. Be realistic. What precision do you really require? A fan isn't going to start and stop all that repeatably so why do you care? \$\endgroup\$
    – Transistor
    Mar 29, 2021 at 14:56
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    \$\begingroup\$ Does this answer your question? General directions for a timer circuit which will not use microcontroller and which can measure several hours needed \$\endgroup\$ Mar 29, 2021 at 15:25

3 Answers 3

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Use a CD4060 instead by itself - it has a built-in oscillator so you don’t need the 555. Then gate the circuit to get the one-shot behavior you’re looking for.

MORE: To get an accurate time, use two CD4060s.

  • use a 'watch crystal' with the first one to make a 2Hz signal
  • use the second one to count down from 8Hz (more on why, below.)

Here's the first part to make the reference:

enter image description here

From this Q: Calculating Rs Value for 32kHz Pierce-Gate Crystal Oscillator Circuit

Now comes the second part. Take the 8Hz output (Q11) and feed it to a second 4060. Then that device has outputs that toggle as follows:

enter image description here

Now, you can decode count = 3600s, that is, one hour, as (2048 + 1024 + 512 + 16) off the second device when we see Q13, Q12, Q11 and Q6 = high.

Now, I explain why I chose 8Hz to the second stage: because I wanted to decode counts 2048, 1024, 512 and 16, and you'll see that Q10 isn't pinned out, so I scaled the counter bits so I didn't need to look at Q10.

This will give a 100's of PPM accuracy due to the watch crystal. I'll leave the rest of the design up to you, but I suggest using flip-flop with async set/reset to control MR and your device:

  • push button: set flop, Q=1=device on; Qn=0=MR, counter runs
  • decode count = 3600: reset flop, Q=0=device stops; Qn=0=MR, count stops
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  • \$\begingroup\$ But the internal oscillator is not very accurate with R-C components, and not stable over temperature. AND - there is no crystal that divides down to a 1-hour period in only 14 stages. \$\endgroup\$
    – AnalogKid
    Mar 29, 2021 at 15:59
  • \$\begingroup\$ Could you please elaborate more the one-shot behavior? \$\endgroup\$ Mar 29, 2021 at 20:13
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    \$\begingroup\$ You want the circuit to stop counting when Q14 goes high. You can do that by using an open-drain FET to stop the oscillation. There are many examples of this if you search. Also, you can cascade CD4060s and use a shorter time constant that’s easier to control. \$\endgroup\$ Mar 29, 2021 at 20:21
  • \$\begingroup\$ @hacktastical, aright I will test it and come back to you again. Thanks in advance. \$\endgroup\$ Mar 29, 2021 at 20:38
  • \$\begingroup\$ Extended the comments. Summary: 2 CD4060 chips, a watch crystal, a 4-input AND (or three 2-input AND), a flip-flop. \$\endgroup\$ Mar 29, 2021 at 21:52
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1 Hour Monostable

Components on the left produce a negative going pulse when SW1 is pressed which sets the RS latch and sets the counter running.

C3 ensures counter is in reset at power-up.

Set VR1 such that Q4 goes high 14 secs after SW1 is pressed which will ensure that Q12 goes high just about an hour after SW1 is pressed.

After an hour, when Q12 goes high, it will reset the RS latch which resets the counter ready for the next press of SW1.

High going, 1 hour output pulse available from output of IC2b. Low going, 1 hour output pulse available from output of IC2c.

C2 is a bipolar (non-polarised) electrolytic.

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A 9.545 MHz crystal (Digi-Key: 69 cents) in an oscillator, divided by 2^36 (a 36-stage binary divider string) yields a frequency of 0.500033 cycles per hour. IOW, 1/2 cycle of the output is 1 hour +/- 1/4 second. With cheap off-the-shelf parts, don't get more accurate than that.

A CD4060 oscillator section can run at 10 MHz, barely, and gets you the first 14 divider stages. After that, a CD4521 has 24 stages, 2 more than needed. Last, a quad NAND gate to form the control flipflop.

3 chips, dead-bang accuracy, $10. Requires Vdd = 12 V.

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  • \$\begingroup\$ Sounds pricey. OP will take MCU. Wouldn't an 80p 8-pin MCU and £1 crystal be smaller, have far fewer solder joints, be much cheaper, more flexible and just as accurate? Mind you, I have disregarded the software development/maintenance costs which in a company are notable, even for 5 lines of application software. \$\endgroup\$
    – TonyM
    Mar 29, 2021 at 16:08
  • \$\begingroup\$ Time ago I simulated and built the following circuit by David A. Johnson: discovercircuits.com/DJ-Circuits/astable.htm You might want to try this as well: discovercircuits.com/DJ-Circuits/10secosc.htm Here's a list of many other oscillators by David A. Johnson: discovercircuits.com/O/o-astable.htm \$\endgroup\$ Mar 29, 2021 at 16:48
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    \$\begingroup\$ Tony, I just checked the original post. Quote "I prefer suggestions with discrete hardware components over the microcontroller suggestions". And the $10 estimate is high, but I don't know his parts situation. And, of course, zero firmware development. Gold star for mentioning that cost; many gloss over it. \$\endgroup\$
    – AnalogKid
    Mar 29, 2021 at 17:01
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    \$\begingroup\$ Some always say "MCU!", I like designing in response to assessed requirements. Hence I listed size, cost, assembly and flexibility and why I read the question carefully before I commented...but in quoting it, you appear to have pretended the half you don't want isn't there: "I prefer suggestions with discrete hardware components over the microcontroller suggestions in general, but if it is the most suitable solution, please share with me". We adjust our views to fit the facts, not the other way around. Btw, it's far more fun to make one out of 4060 etc, just harder work for OP to make:-) \$\endgroup\$
    – TonyM
    Mar 29, 2021 at 17:32

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