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timed light circuit

timed light circuit

timed light circuit

(OP)
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?

RE: timed light circuit

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

RE: timed light circuit

Look at DigiKey for timers (www.digikey.com) or Mouser (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
 

RE: timed light circuit

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

RE: timed light circuit

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

RE: timed light circuit

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

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