A Variable, On/Off Timer

Created "Dec 9, 2010".
New Revised Circuit at bottom of page, "August 12, 2014 

More Adjustable Timer Circuits using a CD4541B IC.

This Circuit has adjustable "On and Off" times and is capable of Very Short
to Very Long settings, and it keeps Repeating this sequence continuously.

I designed this circuit to control some home made "2 foot by 4 foot" heater panals in my garden.
These heaters are Low Power (50 Watts each) and with a bit of insulation over them,
they keep the earth from Freezing, even at -30 degrees Celsus. (About -23 F)

This is just so I can dig up my Carrots, Beets and Parsnips, All Winter long.
Its Great to have FRESH Vegitables All winter long.

I am quite sure these timers can have MANY other applications also.
And the Resistor/Capacitor Values can be changed to create much longer or shorter times also.



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The Schematic.
This Circuit Randomly starts in Either the "ON" or "OFF" State.
This also gives Formulas for the On & Off Time calculations.

The PCB.

Overlay Picture.



My Revised Version.
When turned On, this Always Starts with "ON" State.

The Revised Schematic.
This also gives Formulas for the On & Off Time calculations.

The Revised PCB.

The Revised Overlay Picture.





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 Chemelec 
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