Timer Circuit

Thread Starter

Arjun_Reddy07

Joined Aug 21, 2022
5
Hello,

I am trying to make a timer circuit that can hold a FET or a relay high for 4 hrs. and low for 4 hrs.
555 timer is the option I have so far and want to make sure that it can stay that long. are there any better options ?
 

MisterBill2

Joined Jan 23, 2018
13,144
Several questions come to mind: The first is just how accurate does the timing need to be, and then is this to be on and off at specific times, or just simply alternate actions? There are two quite different approaches depending on which mode is required.
 

Ian0

Joined Aug 7, 2020
6,315
Assuming “4hrs” means somewhere between 3.5 hrs and 4.5hrs (otherwise it would have been specified as 4.0hrs, or 240 minutes) then the 4060 circuit (post #2) should be adequate.
 

Ya’akov

Joined Jan 27, 2019
6,575
Because it must be said by someone…

An 8-pin MCU like the ATTiny85 or 13A with an RTC would be very flexible, reasonably accurate, and relatively easy and cheap. If you don’t need to be minimalist in the packaging, then a Digistump ATTiny85 development board* or clone (which is still very small) and a DS1307 RTC module (also not very large) would do the job nicely. Both of those have very good Arduino environment support which makes programming very easy, and in your case the program would be trivial while also offering a lot of flexibility.

This could also be done with the bare components (i.e. ATTiny85 MCU dip or SOP package, the DS1307 chip and supporting passives, etc.) on your own PCB. The ATTiny85 can still nbe programmed in the Arduino IDE as well.

*The board at the link is intended as an example. They can be found cheaper if speed of shipping isn’t critical, and there is another form factor that includes a MicroUSB female port instead of the integrated type A male.
 

MisterBill2

Joined Jan 23, 2018
13,144
Adding an "AND " gate to the CD4060 circuit in post #2 is a simple way to gain a longer delay time with a faster clock frequency, because you can use the sum of the binary counts. There does need to be a change in that circuit to provide the alternating on/off function requested. That circuit is only for a single time period, after that it must be reset.

Using a digital clock IC that provides BCD outputs would be a way to be accurate within a second.

Now another question: Can the timer be mains powered or does it need to be battery powered. Mains power is an easy source of either a 50 0r 60 cycle clock signal is why the question.
 

Thread Starter

Arjun_Reddy07

Joined Aug 21, 2022
5
Several questions come to mind: The first is just how accurate does the timing need to be, and then is this to be on and off at specific times, or just simply alternate actions? There are two quite different approaches depending on which mode is required.
It's a battery operated LED circuit that needs to be powered. It needs to shut off after 4-5 hrs to not completely deplete the batteries and allow them regain.
 

Ya’akov

Joined Jan 27, 2019
6,575
It's a battery operated LED circuit that needs to be powered. It needs to shut off after 4-5 hrs to not completely deplete the batteries and allow them regain.
In that case maybe it would be better to monitor the SoC of the battery and shut down based pin that instead of time.
 

MisterBill2

Joined Jan 23, 2018
13,144
OK, now we have a very important piece of information about both power and application. Certainly "Y" is correct, presuming that it is possible to access the battery packs. Otherwise, some sort of timer using a CMOS IC like the CD4060 will make the most sense. There are also now quite a few very low power ICs that will awaken periodically from a sleep mode to execute some task, and then return to sleep mode. While I am aware of them I am not familiar enough to offer suggestions in that area. They are often referenced as "Low Iq" devices, meaning low quiescent current designs. So that is probably a good area to investigate.
 

Thread Starter

Arjun_Reddy07

Joined Aug 21, 2022
5
Adding an "AND " gate to the CD4060 circuit in post #2 is a simple way to gain a longer delay time with a faster clock frequency, because you can use the sum of the binary counts. There does need to be a change in that circuit to provide the alternating on/off function requested. That circuit is only for a single time period, after that it must be reset.

Using a digital clock IC that provides BCD outputs would be a way to be accurate within a second.

Now another question: Can the timer be mains powered or does it need to be battery powered. Mains power is an easy source of either a 50 0r 60 cycle clock signal is why the question.
Adding an "AND " gate to the CD4060 circuit in post #2 is a simple way to gain a longer delay time with a faster clock frequency, because you can use the sum of the binary counts. There does need to be a change in that circuit to provide the alternating on/off function requested. That circuit is only for a single time period, after that it must be reset.

Using a digital clock IC that provides BCD outputs would be a way to be accurate within a second.

Now another question: Can the timer be mains powered or does it need to be battery powered. Mains power is an easy source of either a 50 0r 60 cycle clock signal is why the question.
The whole idea is to have a battery operated device. No programming, cause that increases the complexity.
 

Thread Starter

Arjun_Reddy07

Joined Aug 21, 2022
5
Adding an "AND " gate to the CD4060 circuit in post #2 is a simple way to gain a longer delay time with a faster clock frequency, because you can use the sum of the binary counts. There does need to be a change in that circuit to provide the alternating on/off function requested. That circuit is only for a single time period, after that it must be reset.

Using a digital clock IC that provides BCD outputs would be a way to be accurate within a second.

Now another question: Can the timer be mains powered or does it need to be battery powered. Mains power is an easy source of either a 50 0r 60 cycle clock signal is why the question.
The whole device is powered by batteries in series adding to 5V.
And the idea is not to involve any programming to keep the minimalistic design and low cost.
 

Thread Starter

Arjun_Reddy07

Joined Aug 21, 2022
5
In that case maybe it would be better to monitor the SoC of the battery and shut down based pin that instead of time.
I want mention that the cells I am using are Alkaline, not rechargeables.
Sounds like a good idea to try. But my application needs power conservation. I don't want to turnoff when battery is 30% (lets say) when there is still energy left. I want it to turn off after 4-5hours of operation and reset when a power cycle (turn Off and ON) is performed.
 
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