Hello everybody,
I have a very low-frequency astable oscillating circuit (555) operating at 15V Dc, the on/off times are several minutes (adjustable 20 to 35 mins).
- I wonna build a control circuit to control the supply voltage to the oscillator that operates like a timer to completely power down the entire system after repeating the cycle for 4 times (4 times on) then only reset when main power switch is flipped off then on again.
- One extra option is to have a LED to indicate that the entire routine is completed.
All ideas are appreciated,
Thanks in advance

 

This is a perfect job for a small microcontroller.

 

Keyword- "pulse counter , CMOS " . When 4 pulses are counted, the counter halts oscillator based on 555' timer.

By the way, it's not a good idea to build an astable oscillator with such a low frequency on the 555' . Much better if oscillator works at tens of hertz, and after frequency is divided . CD4017' will do the job. And a lot of other pulse counters.

Or a microcontroller can perform all the job

 

Keyword- "pulse counter , CMOS " . When 4 pulses are counted, the counter halts oscillator based on 555' timer.

By the way, it's not a good idea to build an astable oscillator with such a low frequency on the 555' . Much better if oscillator works at tens of hertz, and after frequency is divided . CD4017' will do the job. And a lot of other pulse counters.

Or a microcontroller can perform all the job

Thanks a lot for the reply, I'll give it a try and let you know. I also know that 555 oscillator at such low frequency is not the best solution but I'm trying to keep it as simple and cheap as possible.
If you can share a simple schematic for the CMOS counter circuit will be much appreciated.
Also any schematic ideas for the extra low frequency oscillator.
Thanks again

 

Thanks a lot for the reply, I'll give it a try and let you know. I also know that 555 oscillator at such low frequency is not the best solution but I'm trying to keep it as simple and cheap as possible.
If you can share a simple schematic for the CMOS counter circuit will be much appreciated.
Also any schematic ideas for the extra low frequency oscillator.
Thanks again

Here is an example :
https://www.electronicsforu.com/electronics-projects/hardware-diy/pulse-generator

Very low frequency oscillators :
https://www.electronics-tutorials.ws/waveforms/generators.html

As you see, circuits are not very simple.
The circuit can be built on a single microcontroller, too

 

I would like to see how a micro can handle the issue of having an LED lit after the power is removed. Battery?

The OP is starting with 15 volts so most likely there will be the need for a regulator, then the need for some external circuit to keep the LED lit and switch the power so you might as well have some fun building the entire thing without a micro.

Also, the term "Main Power" must be defined.

My point is...how much of the BOM will a micro replace?

I can see it replacing the 555 and a 4017 but that is matched by the regulator and the micro.

Then you still need the parts to perform the tasks of switching the power...etc.

 

If the 15 volt supply will stay on, then the solution is fairly simple. use a CD4017 counter IC to count the pulses, and when the count of 4 is reached then the output switches off the power mosfet. Then to start it over, a momentary pulse to the reset of the 4017 resets the counter. You may need to invert the 555 output to the 4017 so that it will switch off when the fourth pulse ends.

 

The circuit is simple in any case, but there is much more info needed.

Such as what exactly is meant by "Main Power Switch".

And is there a task to be performed when the countdown is in progress.

Also, one issue when using a 555 in astable mode right from the first cycle is that cycle is always longer than the rest, so if that is a problem it would have to be solved. Perhaps jigging up the 555 to operate in monostable mode instead.

 

I'm trying to keep it as simple and cheap as possible.

Then it would seem a small, cheap microprocessor for less than a dollar US, which can perform all the desired functions with very few added parts, would be the best solution.
It also would allow the easy addition of added features down the road, if wanted.

Learning to program it will take some effort, but the required program would be relatively simple and should be worth the effort.

 

If you are already skilled in using microcontrollers, it’s a no-brainer.

 

That "cheap processor" requires a non-cheap computer to program it, a non-cheap interface to do anything useful, and non-simple programming experience to make it do anything at all. AND it needs a program loaded in to do anything. The counter IC
MC14017, can operate on the 15 volt supply, and deliver a 15 volt output when the #4 pulse ends. So the input can be to pin 14, the clock enable pi, with pin 13, clock, pulled to +15. The count of 4 output can drive an MPSA13 transistor to enable the "main power shutdown. And then a reset pulse to the reset pin will remove the shutdown signal and the thing is ready to go again.
All the program resides inside the IC., no computer needed.

 

a non-cheap interface to do anything useful,

What "non-cheap" interface?

MC14017, can operate on the 15 volt supply, and deliver a 15 volt output when the #4 pulse ends.

Fine, but you also need the pulse generator and its parts, which must be included in the total.

I'm also generally not an advocate for using a micro for simple functions, but if the TS wants the simplest and cheapest circuit, I think, for this job, that's a small micro.
(I'm assuming he wants to build more than one).

 

So you have a low frequency oscillator that you want to latch up after 4 cycles, and it's run by a 555 at its very limits of low frequency operation.

Solution: Replace the 555 with a CD4060. This is an oscillator plus a 14 stage divider all in one. In round numbers, the timing components will by 1000x more reasonable, and you get both the low freq you want plus a signal that changes state after four counts of your main output.

The 4060 does hot have every one of the 14 counter stages brought out to a pin. For example, Q11 is not brought out, but that is not a problem in this application. The Q10 output is the main clock output signal, and when Q13 changes state it latches off the 4060's oscillator through a diode. The 4060 has a reset input that can do a POR (Power-On Reset).

Schematic later.

ak

 

I agree on looking at the micro, especially if the OP intends on exploring other avenues/circuits.
It is amazing what is packed into an 8 pin microchip now.
I have gone through the path of creating circuits with Descrete devices, just that that was the only option.
But the micro is my first go-to now.

 

I have a very low-frequency astable oscillating circuit (555) operating at 15V Dc, the on/off times are several minutes (adjustable 20 to 35 mins).

Please post the schematic.

ak

 

I agree on looking at the micro, especially if the OP intends on exploring other avenues/circuits.
It is amazing what is packed into an 8 pin microchip now.
I have gone through the path of creating circuits with Descrete devices, just that that was the only option.
But the micro is my first go-to now.

I have yet to learn about any micro processor package that does not require programming, which programming always requires external physical resources and always requires a fair amount of knowledge and skill.
Using a CD4017 requires the ability to read and understand the data sheets and some soldering ability.

 

I have yet to learn about any micro processor package that does not require programming, which programming always requires external physical resources and always requires a fair amount of knowledge and skill.
Using a CD4017 requires the ability to read and understand the data sheets and some soldering ability.

Most creative activities require tools. Is a circuit better because you can build and debug it without a multimeter?

If you need to make 10,000 of something, is it cheaper to use a circuit that costs $1 more, or one that requires $100 worth of new tools?

 

Using a CD4017 requires the ability to read and understand the data sheets and some soldering ability.

No argument there.
But you seem to be ignoring the fact that the job also requires a very low-frequency oscillator.

 

I have yet to learn about any micro processor package that does not require programming, which programming always requires external physical resources and always requires a fair amount of knowledge and skill.
Using a CD4017 requires the ability to read and understand the data sheets and some soldering ability.

All the S/W and instruction is free, the programing device can be had for $30.00!!
The CPU's a $1 ea. !

When transistors first appeared and you needed a simple flip flop, it required a couple of transistors and a handful of R - C's. and time constructing.
But I've moved on since then.

 

If one of the basic requirements is "simplicity" I can't see how learning to code meets that requirement.

Now if the OP already knows how to code then the suggestion to use a micro is like telling a carpenter to use a hammer on the nails.

Of course, someone can provide the code, but that is something I rarely see working out very well.