Hi, I'm an amature trying to make a timer using a 555 cmos in astable mode to light an led at a specific time say 10 hours and then run for around 3 hours and stop. The Vcc should be +6 volts, any help on resistor and cap values would be great as I'm having trouble working out the math. thankyou.
Hi, I'm an amature trying to make a timer using a 555 cmos in astable mode to light an led at a specific time say 10 hours and then run for around 3 hours and stop. The Vcc should be +6 volts, any help on resistor and cap values would be great as I'm having trouble working out the math. thankyou.
Sorry, you won't get 10 hours with a 555 timer on its own. The periodic time depends on the CR product, (seconds = C in microfarads x R in megohms x a constant) and the values for 10 hours are far higher than the 555 can handle.
You need to drive a divider chip from your 555. Your question has been asked before, so do a search for previous answers.
May be in Giga Ohms and capacitor in Farads If you use C = 10,000uF then using formulae:
T_on = 0.693 * (R1+R2) * C
T_off = 0.693 * R2 * C
We get R1 = 4.08 M and R2 = 4.6 M
This I think is practically impossible. I don't think the circuit will be reliable at all.
Well, it can be done using long duration timer IC from EXAR. Its XR22?? along with 555 serving a clock to this IC. I don't remember the number of this IC since I studied it quite long back and have never used it practically. May be some on here knows it.
How about using a 4060, on board clock with RC timing and then binary counting........ timing can be set quite accurately if you use a preset....... or else, a 4047, and 4040 combination......
just a suggestion of course, unless you need to use a 555 8)
Those Exar devices were:
XR-2240 Programmable Timer/Counter: 16-pin DIP, Timing from uS to days, 4V-15V, 0.5% accuracy.
XR-2242 Long Range Timer: 8-pin DIP, Timing from uS to days, 4.5V-15V, 0.5% accuracy.
i have a problem about my project i dont know how to connect them using 555 timer, 74LS92 and 74LS47 driver to make it counting 00-99, so i decide to ask from you guys if you know the diagram. tnx and God bless you