Question about LED Chaser Sequencer...

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criteria101

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This board operates on 3-12 volts. Appears to be using a 16F688 PIC. It appears designed for use with 8 5mm LEDs, but I was wondering if I could expand it to 16 LEDs, preferably 3mm or 1.8mm. Basically just adding a second to each of the current outputs. Would I just need resistors to do this?



Here is a link to the product: Led Chaser Sequencer YELLOW

Thank you.
 
It depends on what current is already been taken by the single LED's - check the values of R1.
 
I presume that if you pair up two leds per output, you will not be disappointed if they light at the same time (there are not enough outputs on the PIC to do otherwise).

Note the Resistor pack R1. You would need another just like it, and your eight new leds would fed through the eight resistors inside it...
 
Will the replacement LEDs be yellow too? Also I know you wrote that it can operate on 3 - 12V but what supply voltage do you actually plan on using?
 
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vne147 said:
Will the replacement LEDs be yellow too? Also I know you wrote that it can operate on 3 - 12V but what supply voltage do you actually plan on using?
Click to expand...

I would be using 9v. and the LEDs will be red and blue.

The 16f688 has a 25ma limit per pin.
 
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So your end result is that you want a pair of LEDs to light up at a time? If that's what you are looking for it can probably be done with the existing circuit. It looks like the board has a voltage regulator that feeds supply voltage to the PIC and the LEDs are direclty driven from the PIC's I/O pins through current limiting resistors in the resistor network R1. You probably won't be able to place the two LEDs in each pair in series because the volatge regulator output is like too low. You can place each LED in the pair in parallel with a small maybe 1Ω resistor per LED. It would be nice to know the actual volatge output of the regulator and the value of the resistors in the R1 resistor network.

If you want 16 LEDs to light up individually in sequence, it would be difficult to modify this circuit to do that for you.
 


Here is how I expand the ports for more outputs:
 

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