Simple LED Push Button Sequence

audioguru · Apr 18, 2009

colin55 said:
How much more current do you want to deliver?

Use 12v, if you want to deliver 20mA from the chip.

No.
The max allowed dissipation in each output transistor in a CD4017 is 100mW. With a 12V supply the voltage across an output transistor is typically 8V when the current is 20mA. Then the power in the output transistor is 8V x 20mA= 160mW and the output transistor will melt.
A current-limiting resistor must be used to share the heat.

Roff · Apr 19, 2009

jmb4370 said:
In the "push to advance" LED circuit like in Ron's post #9, each LED stays ON until the next one is lit with another push of the momentary swtich, as the OP asked for. Besides connecting a 555 as a monostable to each emitter of the outputs, is there another simpler way to make the different LEDs lite up for just a brief moment, say 0.1 second?

You can make the pulse width of the debouncer 555 the required width, then AND or NAND each 4017 output with the output of the 555. The gate outputs can drive the LEDs directly, or through transistors.

jmb4370 · Apr 19, 2009

Thanks! I actually understand that, and looks like a good way to go.

Addiing the separate 555's to each output would allow each output to have a different pulse width if that function were desired.

Simple LED Push Button Sequence

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Simple LED Push Button Sequence

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