Hi guys,I need to build a timer that can come on for a few seconds every 24hours . Can this be done with the 555 ic? If possible can you point me in the direction of a circuit diagram please

 

You cannot get a period of 24 hours from a '555.
You could use a CD4060 which is a combined oscillator and 14 stage divider. If you set up the oscillator to run at about 5.27Hz the '4060 will complete a full cycle in 24 hours. Then use the Q14 to trigger a monostable (possibly a '555) to get the 'few seconds' pulse output.

 

No. A 555 is only good for a few minutes at best.

Does it have to be exactly 24 hours?

If not, you can use a CD4060 circuit such as this.
It can trigger a 555 timer to give you the few second pulse you want approximately every 24 hours.
For that, you don't need the relay. The transistor can trigger the 555 directly.

Edit: AH beat me to it.

 

Hi guys,I need to build a timer that can come on for a few seconds every 24hours . Can this be done with the 555 ic? If possible can you point me in the direction of a circuit diagram please

How about a lamp timer that comes on once a day, to power a 555 circuit that runs for a few seconds. Cheap and easy, if it meets your needs.

 

How about a lamp timer that comes on once a day, to power a 555 circuit that runs for a few seconds. Cheap and easy, if it meets your needs.

I like it.
If it's not obvious, the 555 circuit can be powered by a wallwort supply that plugs into the timer.
You probably have one laying around in your junk box that would work.

What is this pulse going to do?

 

Here's the LTspice simulation of a simple 555 timer circuit that gives about a 3 second pulse when powered up.
The time can be adjusted by changing the value of R2 and/or C1.
The operating voltage is not critical and can be anywhere between 5V and 18V.

 

You could use a CD4060 which is a combined oscillator and 14 stage divider. If you set up the oscillator to run at about 5.27Hz the '4060 will complete a full cycle in 24 hours. Then use the Q14 to trigger a monostable (possibly a '555) to get the 'few seconds' pulse output.

If you cut the 4060 osc freq in half and add two diodes and one resistor, you can eliminate the 555. Now, 1/2 of the Q14 output cycle equals 24 hours. Diode-OR Q5 and Q14 into the Reset input for a 6 second output pulse on Q4.

ak

 

If you cut the 4060 osc freq in half and add two diodes and one resistor, you can eliminate the 555. Now, 1/2 of the Q14 output cycle equals 24 hours. Diode-OR Q5 and Q14 into the Reset input for a 6 second output pulse on Q4.

ak

Shouldn't that be a diode and?
I think you need something more complicated than that. The Q4 output will be pulsing for the whole 24 hours. Diode and Q4/Q14 for the output perhaps?

 

Shouldn't that be a diode and?
I think you need something more complicated than that. The Q4 output will be pulsing for the whole 24 hours. Diode and Q4/Q14 for the output perhaps?

Correct, it is a diode-AND. Q14 goes high after 24 hours and stays there (for the next 24 hours unless something resets the circuit). Q5 goes high after Q4 has been low and then high and then goes low again for the first time after Q14 went high. Now Q14 and Q5 are high, and a pullup resistor pulls the Reset input High. Everything immediately goes to zero, removing the reset signal in less than 1 us, and the cycle restarts. This is in several of my previous posts; I'll find one.

Just a minute ... just a minute ...
The *period* of the 4060 oscillator is equal to the desired output pulse. My standard circuit for long delays requires that the minimum output pulse be at least 8 times the osc period, so it will not work in this application. However, a gate package can be used instead of a 555 to gate out one clock pulse every timer cycle. Hmmm...

ak

 

What is the output of the timer doing or driving? LEDs, buzzer, relay...?
What is the power source for the circuit?

ak