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increment/decrement counter

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I'm trying to put together a project for some students, and it's a bit out of my field. The portion that's stumping me right now is to get a counter that also backslides.

The output is 8 LEDs. Everytime we receive a pulse, the number of lit LEDs should increase by 1. However, every two minutes (or so, adjustability would be nice), the number of lit LEDs should automatically decrease by 1.

The more compact the circuit the better - we're space limited in the housing.

Thanks for your help.


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Look at these links.

led counters
The Last circuit is closest.
If you use a switch debouncer circuit instead of the timer it will count up when you push the button . Use a delayed on timer with a reset triggered by the same debouncer for the down sequence then you will have your circuit. The only problem is resetting the whole circuit. I think you can just turn off the power to reset the sequence. ???





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Thanks for the leads. I looked them over, and the first one is for a numeric display, which is too tech-y for what we want. The second looks to be a binary counter, which is also not quite there. The last knight-rider diagram is really cool, and I may build one for another project, but also not quite right.

I think I may not have described it quite enough.

Think of the LEDs as the counters from a battleship game...

0 = oooooooo
1 = xooooooo
2 = xxoooooo
3 = xxxooooo
4 = xxxxoooo
5 = xxxxxooo
6 = xxxxxxoo
7 = xxxxxxxo
8 = xxxxxxxx

So the number of lit LEDs tells you the number you're on.

Thanks again for all the help.


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I think that is a shift register with a parallel ouput going to the LED's. The input to the register is pulled high. Each pulse will send a high that migrates through the shift register. At the end, all the LED's are lit and the device needs to be reset. This is a way of counting clock pulses where the clock shifts a one instead of shifting the sequence.

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If we could figure out a way to use a button to increase voltage every time you push it and have a capacitor discharge timer to decrease the voltage slowly unless the button was pushed again we could use a Bargraph Display Driver like the LM3914 ,5 or 6 to do the job. Look at the Datasheet for more Ideas.




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Hmmm... The bar displays look interesting, but I think would be difficult to run off a battery. I spent the weekend looking over the shift register information, and think that the best solution would be a bidirectional 8-bit shift register, with some sort sort of limiter that when all 8 LEDs are lit, it doesn't increment any more. Same limits on the decrement function, so that when none of the LEDs are lit, we don't fall further below zero.

Would something like http://www.eelab.usyd.edu.au/digital_tutorial/part2/register06.html work, but expanded out to 8 bits? I'm still not sure what the limiters would look like, but I'm still fumbling along...

Thanks for all the continued suggestions, I appreciate them!


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