Long OFF_time timer by 555

Hi to all
Dear friends, I want to have a timer which the OFF time of the output should be 1 hour and ON time to be 10 sec. It should be implemented by IC 555.the accuracy of mentioned times is not important ; OFF&ON times can be higher or lower but not too much. Help me if you have such circuit.

Hi,

If it must be with a single 555 timer IC, then you go for the conventional astable multivibrator circuit. It's everywhere on the internet along with the timing formula. You're just going to need a lot of capacitance.

TIP: You need a duty cycle of less than 0.5 so look for the circuit that offers this. You're going to have diode in such a circuit.

A second option is to use string of digital triggers with the timer to divide the frequency. The digital triggers will activate the power supply on the clock for 10 sec per hour.

Hi,

YOu can reduce the ON time with a diode.
"Diode D connected in parallel to Rb is only used when an output of duty cycle less than or equal to 50% is required."

One hour is a very long time for a 555 timing cycle. I think 20 minutes is the maximum suggested in application notes. It will be very inaccurate with such a large capacitor. The recommendation is to cascade two to four 555s for long time delays.

There is a lot of information on the Internet you can quickly research and find suitable circuits in less than 5 minutes.

The 555 cannot reach such a long period on its own. Capacitor leakage will not allow your circuit to work. You will require "helper" logic.

If you do a 10 second astable circuit (perfectly doable with a 555) and follow it with a common binary counter and some gates, then you decode 1 pulse out of 360.

I agree a NE555 would struggle to produce timing as long as that but the CMOS version might be able to. The timing would be very imprecise and subject to environmental conditions though. A better solution is a simple MCU which would cost about the same as a 555 but be thousands of times more accurate or to use something like a CD4060 and some logic gating to select 10 seconds out of every 3,600.

Brian.

A CD4541 will provide LONG Time Delays

betwixt said:

I agree a NE555 would struggle to produce timing as long as that but the CMOS version might be able to. The timing would be very imprecise and subject to environmental conditions though. A better solution is a simple MCU which would cost about the same as a 555 but be thousands of times more accurate or to use something like a CD4060 and some logic gating to select 10 seconds out of every 3,600.

Brian.

Click to expand...

Mr. Brian could you please give me such circuit with 4060 or other ICs?

Hi,

Sorry, I'm truly sorry to be tactless and forthright. I have to ask very sincerely: Do you actually ever try to research or make a circuit yourself or just first ask a lazy guy question here and then latch onto members here (and rudely ignore many other valid suggestions) and ask them to make your circuits after getting advice on how to do it yourself? Do you get paid for the stuff you ask others to provide turnkey solutions for here on this forum? I don't want to sound rude but I find your general approach lazy and a bit rude/arrogant, especially for a person who calls themself Dr. - someone I can only assume wishes to infer he has a doctorate in something.

Recipe ingredients:
· Three ICs: 2 x LMC555, 1 x CD4017
· Passive components: as seen in every of the millions of 555 schematic on the Internet.

Mixing and cooking instructions:
1) Make a 3mins on, 3 mins off astable timer. Place a diode across the relevant resistor to make the high pulse as short as possible.
2) Feed that signal into the clock pin of a CD4017.
3) Connect a monostable 555 input to pin 11 of the CD4017. Select timing components to create a 10 seconds on pulse.
4) Experimentally perfect the basic idea either with a simulation tool and then a breadboard or just with a breadboard.

That's about it.

If someone as hopeless as myself with no formal training nor university education can try to make these things and get them to work, be confident, I'm sure you can make such basic circuits, too.

Hi,

Really don't want to seem unpleasant, to you or anyone. Here is a circuit that works in simulations (and therefore, from my real-world experience of this exact kind of circuit, with fine tuning of timing components only, will work). Do expect a little unpredictable drift of the 3mins on/3 mins off "clock timer" as 66uF is not a precise method of creating timing. For greater repeatable precision, the way around that would be to make that first astable timer far less time (half the capacitance or much less, preferably - I don't like going over 10uF with 555s), and connecting it to another CD4017 stage to get another 10 (really 9) time stages out of the whole circuit - roughly 180 second (3 minutes) long on and off clock pulses rather than 360 seconds (6 minutes) long. You could use a CD4060 (divide by x ripple counter) instead of the 4017 I recommend, and use an astable 555 as the clock rather than RC network or XTAL for the 4060 - but, this can become quite annoying as working out the clock timing based on repeatedly multiplying or dividing an initial clock pulse length or the desired time by 2 can result in repeatedly getting results that give frankly unrealistic clock times to create, especially with passive components, like e.g. 6.25 seconds and so on.

I hope you can use this, it is a complete schematic and exactly what you have asked for.









- - - Updated - - -

The schematic says TLC555. This is not a common 555 and I do not recommend it. I only use it as it is the least annoying version to use in the simulator due to pinout and similarity to SE555 and LMC555, a simulation with the TLC555 should always work in the real world with the TTL (NE, SA, etc.) and CMOS (LMC) versions I've used a lot. While most often used and seen in schematics are the NE555, SE555, SA555 and LM555, these are not as good for timing circuits as the LMC555. LM555 is the same as the SE et al 555s, it's not at all the same as the LMC555. LMC555 is CMOS and frankly, more precise; only "downside" is its output power is only 100mA, not 200mA as in SE/SA/LM/NE - but it's not common/recommendable to make circuits feeding the timer output to high power-draw devices as it lowers the device's output voltage a lot, it's better to use the 555 as a power source driver (e.g. for a BJT or MOSFET driving whatever is used) rather than as the power source itself.

Good luck with the endeavour!

- - - Updated - - -

Hi,

Whoops, fuzzy division in last post, to add a second CD4017 would be a(-nother) divide-by-ten, not a divide-by-two result. This is a two-stage version using two CD4017s - the astable timer capacitance is divided by 10, the gain in accuracy and repeatability is really worth the few extra parts and PCB space it requires. To add a third CD4017 would mean the astable capacitor were around 660nF - even better for repeatable timing events that don't constantly go over and under the estimated 1 hour required. Given that most ICs come in packs of 2 or 5 or 10, it's not a bad idea.



My objection to the CD4060:
1hr = 3600 seconds. Start dividing down to get a sensible clock for that with an RC combination that won't be wildly inaccurate each hour, and forget using a crystal for such long times with one 4060, even a 555 needs an unrealistic RC clock to get 1 hour...

3600s/2 = 1800s
1800s/2 = 900s
900s/2 = 450s
450s/2 = 225s
225s/2 = 112.5s
112.5s/2 = 56.25s
56.25s/2 = 28.125s
28.125s/2 = 14.0625s
14.0625s/2 = 7.03125s
7.03125s/2 = 3.515625s

- I've tried this and frankly, getting anything usefully near 3.515 seconds from a resistor and a capacitor is nonsense on more than one level, for that it's best to use a PIC or whatever similar device than can do precise time. That's why I'd use the 4017.