Sound to light unit

[Rushmoore]

Hi there,

I am making this circuit, but want 4 blue leds instead of 4 read ones. Would I need to change anything in the circuit to accommodate for this? Here is the schematic:

Thanks!!

Evie

 

[Alec_t]

That circuit would be very marginal even with red LEDs. Blue LEDs have a higher forward voltage (Vf) than red ones, so you would need to arrange them as 2 parallel strings of 2, rather than 1 string of 4 as shown. Each string would need its own current-limiting resistor. The resistor value would be given by (9-2*Vf)/I, where Vf is the blue LED forward voltage and I is the required LED current in Amps.

 

[KJ6EAD]

Evie, I recognize this is the schematic from the Velleman MK103. Are you intending to build on the kit PCB or design your own?