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bob_monsen
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I'd use 3 4017 counters, chained together. Just clock the chain from your microcontroller. The 4017 is very cheap, has an output for each LED (so no decoding), and can be set up very easily to be chained. You would need 3 for your application. The 23 pin output should just reset them all to restart the count.

Edit: You might be able to hack up something using diodes and pull-downs to test whether the 'reset' (ie, the 23 output) is high using the clock pin. A diode from 23 to the clock output through a 10k resistor, with a 100k resistor at the pin as a pull-down. When the clock is being driven low by the uC, momentarily change it to an input. If it stays low, it's not the end yet. You might also have to test 24 (ie, have them both connected to clock through a diode and 10k resistor) since the pullup will probably clock it again (but only once, until you drive it low again). Not sure, haven't tried it, but probably.

Much easier just to blow another uC pin to test 23, but you said you didn't want to do that.

I'd use 3 4017 counters, chained together. Just clock the chain from your microcontroller. The 4017 is very cheap, has an output for each LED (so no decoding), and can be set up very easily to be chained. You would need 3 for your application. The 23 pin output should just reset them all to restart the count.

I'd use 3 4017 counters, chained together. Just clock the chain from your microcontroller. The 4017 is very cheap, has an output for each LED (so no decoding), and can be set up very easily to be chained. You would need 3 for your application. The 23 pin output should just reset them all to restart the count.

Edit: You might be able to hack up something using diodes and pull-downs to test whether the 'reset' (ie, the 23 output) is high using the clock pin. A diode from 23 to the clock output through a 10k resistor, with a 100k resistor at the pin as a pull-down. When the clock is being driven low by the uC, momentarily change it to an input. If it stays low, it's not the end yet. You might also have to test 24 (ie, have them both connected to clock through a diode and 10k resistor) since the pullup will probably clock it again (but only once, until you drive it low again). Not sure, haven't tried it, but probably.

Much easier just to blow another uC pin to test 23, but you said you didn't want to do that.

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bob_monsen
  • 351
  • 1
  • 5

I'd use 3 4017 counters, chained together. Just clock the chain from your microcontroller. The 4017 is very cheap, has an output for each LED (so no decoding), and can be set up very easily to be chained. You would need 3 for your application. The 23 pin output should just reset them all to restart the count.