View Full Version : Simple adjustable timer

05-31-2011, 11:25 AM
As i am in a process of making a UV LED lightbox these days, i was looking for a convenient timer circuit for an automatic turn-off feature. I found many simple solutions using just one 555 timer and a few components, and many elegant ones using a PIC16F84 and a 7-segment display. I decided to use this circuit that uses a 555 timer and a 4020 counter. The PCB and schematic are in the attachment. The PCB has a few differences than the schematic, but nothing to worry about. I don't have a specific reason for using this circuit, maybe because of it's versatility or something else, i just liked it when i saw it.

06-01-2011, 03:53 AM
good , please explain some application

06-01-2011, 06:41 AM
I will use this circuit to delay turning off a grid of about 230 UV LED's after some time. I ordered a lot of 1000 LED's from ebay a few days ago, 34 dollars. If you read carefully in the PDF file with the schematic there is an explanation of how this works. When you have soldered the last part to the PCB, you select the mode you want, the delayed turn-on or turn-off. Then power up the circuit with the 3mm LED jumper connected. It should be flashing. Then with the trimpot you adjust the flashing rate of the LED to 1 second (trial and error method). Now with the jumpers around the 4020 counter you can set your circuit for 8, 16, 32 etc. seconds turn-on or off operation. Or you can experiment with the frequency of the 555 oscillator (doesn't have to be 1Hz) and number of counts the 4020 does to get shorter or longer delay times for the relay.

Hope this helps.

06-02-2011, 05:03 AM
Some parts soldered other will be tomorrow. Only thing left is to find a suitable 12V supply...


06-03-2011, 10:32 AM
the board is done :D


06-06-2011, 10:51 AM
good job