# Cycling Through a Series of LED's with Each Button Push

#### Sir Kit

Joined Feb 29, 2012
188
I have a momentary button that pulls low to trigger individually, in sequence, a series of 6 logic functions. So I know what function has been triggered, I would like the button to also cycle individually through 6 LED's, returning to the first upon the 7th push.

Can someone please tell me what type of circuit would do this. Available power is 12VDC.

#### dl324

Joined Mar 30, 2015
17,017
What is the desired LED current?

#### crutschow

Joined Mar 14, 2008
34,715
Do you have a separate signal output for each step of the sequence.

#### Sir Kit

Joined Feb 29, 2012
188
What is the desired LED current?
Not critical. Anything that visibly lights up.

#### Sir Kit

Joined Feb 29, 2012
188
Do you have a separate signal output for each step of the sequence.
Not to the LED's. They just need to light in sequence.

#### wayneh

Joined Sep 9, 2010
17,498

What is Vcc? Is there any way to eliminate the LM317?
Yes, the LM317 is not needed. A current-limiting resistor for each LED is the more typical solution. Vcc is just the voltage of your power supply.

#### crutschow

Joined Mar 14, 2008
34,715
Not to the LED's. They just need to light in sequence.
So the LED lit doesn't need to correspond to a particular logic state?

#### dl324

Joined Mar 30, 2015
17,017
Not critical. Anything that visibly lights up.
CD4017 outputs will source 1-2mA with a 12V supply. If you don't use more than that, you don't need extra circuitry to drive the LEDs.

#### Sir Kit

Joined Feb 29, 2012
188
Yes, the LM317 is not needed. A current-limiting resistor for each LED is the more typical solution. Vcc is just the voltage of your power supply.
I would use a CD4017 as shown below. The LM555 would be replaced by a momentary switch.

If Vcc is 12VDC can I feed that straight into the clock input? If that is too high, I also have 3.6VDC in the circuit. Would that be too low?

Given the 12VDC Vcc, what would the voltage output to the LED's be?

In response to crutschow, the LED's only need to indicate the number of times the momentary switch has been pressed. For example, after six pushes the sixth LED lights. One more push and it restarts at number one.

#### dl324

Joined Mar 30, 2015
17,017
The LM555 would be replaced by a momentary switch.
You'll need to debounce the switch.
If Vcc is 12VDC can I feed that straight into the clock input? If that is too high, I also have 3.6VDC in the circuit. Would that be too low?
CD4017 will operate from 3-18V. As long as the clock signal isn't greater than Vdd it will work.
Given the 12VDC Vcc, what would the voltage output to the LED's be?
Logic HIGH will be about Vdd.

Typical source current at 10V is 2.6mA, but can be as low as about 1mA (at 125C). Assuming a 2V forward voltage for the LEDs (depends on color), 10k would give you 1mA.

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#### wayneh

Joined Sep 9, 2010
17,498
Debouncing the switch will be critical to prevent each press from counting as many make-break counts. A 555 is good for debouncing but it can be done fairly well with just an RC filter.

#### crutschow

Joined Mar 14, 2008
34,715
A simple debounce circuit from the switch is an RC filter as wayneh mentioned.
100kΩ in series with 1uF to ground at the clk input should be sufficient.
To protect the input from excessive current from the cap when power is suddenly removed, add a 1kΩ in series with the input after the capacitor (below).