Hi all,

I'm new to this forum, spent a good 2 hours just now reading and reading and I must say, I'm getting more and more interested in everything on this forum.

Anyway, I have a question for some ideas of how to design a circuit to do the following :

Probably will use 4 AAA batteries for 6V supply. A momentary pushbutton switch triggers an LED to turn on. At the same time, a 555 timer starts a 10 minute countdown before turning the LED off. If the switch gets triggered again, the LED must remain on, but the countdown timer should reset the countdown from 10 minutes again. Ultimately, if the switch is not triggered for 10 minutes, then the LED should turn off. If switch is triggered, the whole thing starts again with the 10 minute countdown.

Can someone provde me with some directions or circuit on how to achieve this?

I'm downloading some of the free PCB design programs now and will play around with it this weekend.

Thanks.

 

hi,
The 555 is not the best device to use for a timer as long as 10 minutes.

A 555 astable could be used to drive multistage divider ic, example, HEF4020, HEF4040 dividers.

Some extra CMOS logic would be required to latch/detect the start pulse and the end count.

How much experience do you have in using logic ic's.?

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

 

Or just a 4060, because it has built in inverters for an internal oscillator.

http://www.coolcircuit.com/circuit/timer_4060/

With modifications.

Ken

__________________
"To invent, you need a good imagination and a pile of junk."
Thomas A. Edison (1847 - 1931)

 

Hi Eric,
I understand how CMOS logic IC's work (I think). But would like to use the "KISS" theory. I figure that using a 555 timer would be simplest, but the only thing is that I can't figure out how to reset the 555 timer count whilst keeping the output high. From what I have read, by triggering the RESET on the 555, the output is reset too. Is it possible to reset a 555 timer count whilst keeping the output HIGH?

Thanks for the reply Ken... I can't figure out how the 4060 would allow me to once again, keep output HIGH whilst resetting the countdown timer.

 

hi,

Use a 4093 or 4001 or 4013 ic as a latch, [the latch is set by the push switch]the output of the latch enables the 4060 to start timing, at the required time the output of the 4060 resets the latch.

The output of the latch also drives the LED, so the LED is lit while the latch is set.

Do you follow this.?

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

 

Thanks Eric, I've got some bits and pieces and playing with it all on a breadboard. Interesting, but also frustrating.

Slight change to my little alarm project. Still want to keep it as simple and as small as possible.

Using the 6V battery supply, a normally closed vibration sensor drives the whole circuit to turn on and off an LED. When there are no vibrations detected, LED is off. If vibration detected (very brief open circuit), latch LED on. If no vibrations detected, start the 2-5 minute timer and when it expires, unlatch the LED to switch it off. If during the timer count, vibration is detected, reset the timer to start the count again but the LED should still be latched on.

I need some ideas on how to do this. I've played with 4013, but I can't work out how to latch the output since when the set input goes low, the output also goes low.

Thanks in advance for any help.

 

I need some ideas on how to do this. I've played with 4013, but I can't work out how to latch the output since when the set input goes low, the output also goes low.

hi,

Draw and post a simple diagram on how you are connecting the 4013.

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/