Circuitboard 1

Component list:
-2xNPN C547 transistors
-2x1.6v LEDs (1 red and 1 green)

-2x 560ohms carbon film resistors

Calculations

-2x 1kohm carbon film resistors

Calculations NOTE# According to the data sheet .2 milli amps is not enough to fully saturate the transistors so instead i needed to use 5mA, therefore had to change the original resistors to suit this change.(the ones above in the component list)

How the circuit works

Relating to the circuit i drew up on lochmaster shown on the right:
when the 12v supply is applied the LEDs do not operate, but when the 1st %v supply is applied the green LED is turned on. This 5v supply is what switches the transistor on which completes the green LEDs 12v circuit which therefore allows the voltage go through the transistor to switch the green LED on because that circuit is now grounded. When the 2nd 5v supply is switched on the same thing happens to this circuit as the 1st LED circuit (12v supply is still on).
Note# the 560ohm resistors are there only to protect the LEDs.

Test procedure
A simple test to see if the circuit is working is a visual test, are the LEDs working when the 5v is supplied?
but to see if the circuit is working "properly" various test can be made with a multimeter. The 1st test i did was a availible voltage test at the LEDs and got 12v which is normal, another test i made was a voltage drop test across the LEDs, the legs of the transistors and across the resistors, all where normal voltages.

Problems
A problem which i encounted was that i had a short somewhere in the circuit, i dignosed this with a multimeter by doing various voltage drop tests. i got 12v across the emitter and the collector which indicated there was a shot somewhere. so to solve this i checked the tracks on the circuit board to find twotracks touching because of some solder, i cleared it with a cutter.


2nd 5v supply applied



both 5v supplys added

Reflection
to improve this circuit i could have placed the components closer together to make the circuit tidier.another thing was my soldering wasnt the best so i would get some practice before i made it.