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I am attempting to build a very simple 4 bit counting machine using a CD4029 ic and a 555 timer. I have built my circuit on a breadboard and everything seems to be working perfectly, however on the power up of the circuit the outputs id the CD4029 seem to be set to random values and not to 0000 as I had expected. I need my counter to start at 0 for the project I am working on. How would I manage to achieve this.

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2 Answers 2

up vote 7 down vote accepted

Set Jam Inputs J1-J4 to 0V (pulldown) then give a short positive going pulse on Preset Enable. That should set the all the outputs to low. Once Preset Enable goes back to 0, pulses on the clock input will cause the counter to count up or down (depending on how you've set UP/DOWN.)

A simple, easy, and not terribly reliable way to do this would be to connect a 100nF capacitor from VDD to Preset Enable, and a 100k Resistor from Preset Enable to ground. Powering on the circuit will cause Preset Enable to go high through the capacitor. This is then discharged through the 100K to ground, bringing Preset Enable back to ground.

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May I ask why this would not be reliable –  popgalop Jul 28 at 15:05
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Not TERRIBLY reliable. It should work, though you might have to play with values for the resistor and capacitor. The unreliable part is that you can't guarantee that a clock pulse won't get lost during the initialization, and if you turn it off then on again quickly it might not reset properly. –  JRE Jul 28 at 15:07

You need to use the preset (jam) lines and pulse to reset the counter to 0000. According to the datasheet:

A logical '1' preset enable signal allows information at the 'jam' inputs to preset the counter to any state asynchronously with the clock.

So you can ground all J lines (J1-J4 - pins 3, 4, 12 and 13) and send a HIGH signal briefly to the PRESET ENABLE line (pin 1), with a push-button, for example.

For more info, see: The 4029 CMOS Counter IC

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