- Tue Mar 17, 2015 7:14 pm
#12143
I'm no expert but I don't think one is required in this case. If you do the maths, 3.3v minus the two LEDs means the resistor would be zero ohms anyway. The point of the circuit is that only one or the other LED is lit depending on whether the gpio is set high or low, and there is a resistor on that part of the circuit.
martinayotte wrote:BTW, this wiring looks very bad : there is no current limiting resistances across the 2 leds ...
I'm no expert but I don't think one is required in this case. If you do the maths, 3.3v minus the two LEDs means the resistor would be zero ohms anyway. The point of the circuit is that only one or the other LED is lit depending on whether the gpio is set high or low, and there is a resistor on that part of the circuit.
- Thu Mar 19, 2015 12:39 pm
#12270
If both diodes were alone across 3.3 supply, yes, the current limiting resistor is probably useless, although good to have one, even only few ohms. But since the GPIO driving them, then the 3.3v is apply to only one LED at a time, so the current limiting resistor is absolutely needed ...
- Thu Mar 19, 2015 12:43 pm
#12271
That's what R1 is for in the diagram?
Could have used one on each arm instead though, I guess.
martinayotte wrote:If both diodes were alone across 3.3 supply, yes, the current limiting resistor is probably useless, although good to have one, even only few ohms. But since the GPIO driving them, then the 3.3v is apply to only one LED at a time, so the current limiting resistor is absolutely needed ...
That's what R1 is for in the diagram?
Could have used one on each arm instead though, I guess.
