# Only one of 4 LEDs are lighting up

Before you ask - I've checked that the LEDs worked before putting them in my circuit. They all work.

I've connected 4 LEDs, shown in the arrangement below, up to my Adruino Lilypad. Pin 9 was used as the + 5V, the "- pin" was used as ground. In the schematic below, the "1" represents pin 9. simulate this circuit – Schematic created using CircuitLab When I start my sketch, I set pin 9 to high to check that all the LEDs are working. (this is a PWM pin so I write, `analogWrite(9, 255);`). At this point, only D5 lights up. If I connect up the two wires connecting R9-D6 and R10-D7, then both D5 and D8 light up... but never D7 or D6?

Doing some basic circuit calcs, the total resistance of the circuit is 100 Ohms (1 / (1 / (100 + 100)) + (1 / (100 + 100))). I'm powering from the usb connection to the computer so power source should be 5 V. Total current draw should therefore be 50 mA? Is that too much? If so, why does only D5 - or D5 and D8 when adjusting the circuit - light up?

• you have 200 ohms in series with the LEDs .... remove one of the resistors in each leg – jsotola Mar 28 '18 at 20:08