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7-segment counter with IC 4029 and 4511

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Daryl Musashi

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Hello everyone,

I am fairly new to electronics and going to make my first larger project at the moment. One main element of it is a 2 x 7-segment-display counting down from a certain value to 0. To realize that I used a 555-timer in astable mode to generate the pulses for the first of my two 4029 ICs. Furthermore I use 2 x 4511 ICs to convert the input for the 7 segment displays.
At the moment I have a running circuit, which counts down from 99 to 0. Now I want to modify the starting value, which can be achieved by putting "high" or "low" to the 4 jam inputs (4, 12, 13, 3) of IC 4029. For example if I want to start with "5" the code for the jam inputs is 0101 (for the jam inputs 4, 12, 13, 3) - I hope I am right?

But in detail I cant get the circuit work. I can try every possible combination of "high" and "low" to the jam inputs 4, 12, 13 and 3 - it always starts counting from 9 to 0 !

I thought for a time that the "Preset Enable" pin needs a permanent "high" if I want to define a certain starting value, but the counter does not count any more in this case. But this is no surprise referring to the data sheet of the IC 4029 I realized, as this behaviour is cleary described in the general description section.

Can anyone please guide me what to do in order to achieve a countdown from a certain value? A simple circuit diagram as an example would be sufficient, too.
 
I just simulated in ISIS... Hers what I ended up with... Works okay!!
Capture.jpg
 
Ian,

at first thank you for your efforts. Primary I realized that I made a little mistake during conversion from decimal to binary - but that doesn't really matter. What matters is the fact, that my circuit looks identically to yours (besides some resistors).

As mentioned in the datasheet of 4029 it does not count if PIN 1 (PRESET ENABLE) is high.

1. I power the circuit (with both 4029 PIN 1 "high"). It boots with my chosen number...fine. But it does not start counting (because PINs 1 stay high).
2. I manually change PIN 1 of the right 4029 from high to low (by switching the wires).
3. As expected it counts down now...fine.

My question is:
How can I switch this PIN 1 automatically from high to low after the circuit is powered? One idea might be another 555 chip, but in bistable mode (then I could trigger when it starts counting down after waiting a certain time).
But I hope there is an easier way to accomplish this. I suppose it exists an easy to implement "flip-flop" IC...? Which one would you suggest?



Ian or ramuna or anyone else:Which (freeware) tool do you prefer drawing schematics? ISIS looks fine, but it seems to cost.

Unbenannt.jpg
 
My question is:
How can I switch this PIN 1 automatically from high to low after the circuit is powered?

Try connecting a 0.1uF capacitor from the supply to pin 1 and a 10k resistor from pin 1 to the 0v line.

JimB
 
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