timed light circuit

[bigsteve80]

I want to make as simple a circuit as possible, but can't figure this one out (I'm a ChE, so go easy on me).

I want a circuit with 2 LED's - one red and one green. A clock will turn off the green and turn on the red every 12 hours (at 5 am and 5 pm). If someone pushes a button at any point, the lights will switch, red off, green on, until the next 5 o'clock rolls around. ie: if someone presses the button at 6:00, the green light will be on for 11 hours, but if someone presses it at 4:45, it will only be on for 15 minutes.

I have a 12V DC source.

Any suggestions?

 

[IRstuff]

Is this for school?

TTFN

FAQ731-376

 

[bigsteve80]

No - I want to have a quick way to indicate whether a pre-shift inspection has been done.

 

[zappedagain]

Look at DigiKey for timers (

http://www.digikey.com)

or Mouser (

http://www.mouser.com).

Have a push button activate a relay that turns on/off the LEDs, and then the relay output latches the input (like the button is still pushed) until the master timer resets everything at your 5 AM/PM intervals.

I'm curious how long this can run before you'll need to reset the timing for 24 hour accuracy.

12V is good for LEDs; red LEDs typically need 1.8V, and green LEDs typicaly need 2.1V, so for 10mA through a red LED you'll want a ((12-1.8)V/0.010A =) 1000 ohm resistor in series with the red LED. The green LED will need a ((12-2.1)/10mA = ) 1K resistor. If your LEDs take more or less power then recalculate the current limiting resistor with the above equations.

John D

 

[MikeHalloran]

Because of the real time clock requirement, it might be a good application for an old computer that you'd otherwise discard.

Or just a cron job on one that's already there.





Mike Halloran
Pembroke Pines, FL, USA

 

[VEBill]

Inspection? Use a log book. You can't bring an LED to court as evidence.

 

[IRstuff]

Not only that, but just alternating the colors will make it impossible for any operator to determine whether the operation has been done or not.

TTFN

FAQ731-376