555 timer - Egg Timer Circuit

Thread Starter


Joined Mar 30, 2009
I need to design a circuit that provides timing between 3-6 minutes...the clock needs to be based around a 555 timer.

The timing can be controlled using a variable resistor, however I am wondering how I could go about using digital control.

Any ideas?
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Thread Starter


Joined Mar 30, 2009
Thanks, one more thing...

How could I go about adding a 7segment display arrangement to display the counting process. Would this be overly difficult?


Joined Jul 17, 2007
What circuits are available for you to use?
Do you have 74 series TTL IC's, or 4000 series CMOS?
If 74 series TTL, a 7490 counter and 7447 decoder could work.

If 4000 series CMOS, a 4026 or 4033 IC would be handy.

A digital pot might be a bit expensive for a project like this.


Joined Mar 29, 2009
Instead of a digital pot, could you take the output of a voltage over an analog pot, throw that into an ADC and take the digital output to your counter or display?


Joined Aug 7, 2008
A little wild: Use 2 555's, first counts 30 sec. periods, 2nd inhibits 4017 counter for 2 min. Out "0" not used or tied to a green LED, remainder connected to a ring of 9 LEDs & 9 positions on rotary sw[ digital selection ] , armature to FF for memory, not Q resets, or inhibits 30 sec timer. " Sonalert" connected to Q , FF reset by killing power or PB SW on reset input. Count is from 2 min to 6 min. by 30 sec incriments. Or use 2 4017 , and no 2 min inhibit; as many SW positions and LEDs as desired ; OR ....


Joined Mar 24, 2008
You could also use a CD4052 (dual quad mux/demux, a solid state switch) along with resistors to set the time via binary. You can also use a 1 of 4 or 1 of 8 decoder to program the input. A variable timer would work better though.

Have your read this, 555 Monostable?