# HTM(a)A Arch Section Group Work

## Output Devices

The group assignment was: to measure the power consumption of an output device.

We decided to measure the power consumption of a red LED. We started by opening up the red LED's datasheet.
From here, we found that this LED has a reported power dissipation of 100mW, and we were going to find out if that was true.
We found that the datasheet also reported a forwward voltage (Vf) of 1.8V and a forward current (If) of 20mA.
We measured the supply voltage using a multimeter on the VCC and GND pins of the board: Vs = 5.09 V.
The 470 ohm resistor on the positive leg of the LED had a measured value of R = 466 Ohms (with the board not powered).
We then plugged in the board and measured the voltage drop from the resistor to be Vr = 3.17V.
From this information, we calculated the current from the resistor to the positive leg of the LED using Ohm's Law:
Ir = Vr/R = 3.17/466 = 0.0068 A = 6.8 mA
The power consumption of the LED was then calculated using P = Ir * Vf = 0.0068 * 1.8 = 0.012 W = 12.24 mW.
This means that we were being too conservative with selecting the 470 Ohm resister to limit the current to the LED, and could go with something as low as ~57 Ohms in order to get the 100mW output for a brighter LED.
This was a fun excercise.