3 led on consecutively with different time intervals

Thread Starter

MrsssSu

Joined Sep 28, 2021
200
Above is related from here but this ic only allows the led to be on at the same time interval. Is there a circuit which can help to activate 3 led consecutively for different time intervals. For example, led 1 will on for 3s (the other 2 led will be off), followed by led 2 will be on for 2s (the other 2 led will be off), then finally led 3 will be on for 5s (the other 2 led will be off) and this cycle repeats itself?


Thank you for reading and have a nice day :)
 

djsfantasi

Joined Apr 11, 2010
8,391
Another solution can be made with digital logic. A binary counter, such as a 74LS193, feeds a 4:16 decoder, such as a 74LS154. The 16 outputs are grouped to create the three times, using diodes. Each group drives a transistor for each LED. A 555 provides the clock.

The three times are a multiple of the clock frequency. You may need another counter to divide the clock frequency to obtain the desired times. There is another IC which contains the clock and divider function. I can’t remember which one it is.

Or if you’re into coding, an 8 pin microprocessor, such as an ATTiny45 or 85, can do this with a simple program.
 

crutschow

Joined Mar 14, 2008
30,089
Here's the LTspice simulation of a circuit using the CD4017 decade Johnson counter with the outputs OR'd by resistors to three BJT LED driver transistors to get the desired time intervals.

The 1 second clock can be provided by a 555 astable oscillator as shown in the video.

1657172688461.png
 

Ian0

Joined Aug 7, 2020
5,480
You could also use a 4017 and a 555, and use the 4017 outputs to switch different timing resistors to the 555.
 

Ian0

Joined Aug 7, 2020
5,480
I was going to sketch it, but realised it was Thursday and I had to take the rubbish out!
Rubbish is out for collection and here is the sketch.
2283E749-BD00-4E46-9084-525605A456CE.jpeg
 

Ian0

Joined Aug 7, 2020
5,480
Okay, I see how it works for changing the resistors.
But don't you want the diodes on the bottom side of the resistors to prevent crosstalk from one resistor to the next?
Actually I drew the connection to the LED drive transistors in the wrong place. They should go directly to the 4017 outputs. Then it makes sense.
The 555 needs one resistor permanently between pin 7 and V+ to make sure it can get started if the 4017 starts up with output 7 On, for instance.
That can be the resistor for the slowest state.
Then it needs only n-1 resistors for n states, as the quicker states connect the resistors in parallel.
 
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