Component list
• 1 board
• 2x 470 ohm resistors
• 2x 1k ohm resistors
• 2x c547 NpN transistors
• X2 L.E.Ds (red and yellow)
R13 = 1k ohm resistor
R14 = 470 ohm resistor
R15 = 470 ohm resistor
R16 = 1k ohm resistor
Problems I encountered.
I encountered a problem with one of my L.E.Ds not lighting up and my other staying on all the time. I came to the conclusion that the L.E.Ds where not bright enough due to the 560 ohm resistors. I replaced these with 470 ohm resistors and the circuit worked perfectly. I think this problem was caused by me having on high density L.E.D and one normal.
Caculations I have used
Calculations
R = (sv – Vled) / I
R = (12 – 1.7) / 20
R = 10.3 / 20
R = 51.5 ohms or 515 ohms
B = Ic / Ib
B = 20 / 200
B = 0.1 – 100
.5 – 0.7 = 4.3
R16 = 4.3 / 5 (input voltage)
R16 = 4.3 / 0.005 = 860 ohm - 1k ohm
Test Procedure
To test this circuit I used the Power supply and a Function generator to see if the L.E.Ds would flash individually which they did after I replaced the resistors with smaller ones. Then I did a constant 5v test and took readings of voltage drop across all of the components, these are the readings I got.
R13 = 4.71v
R14 = 10.4v
R15 = 10.65v
R16 = 4.71v
LED1 = 2.16v
LED2 = 1.91v
The voltage drop across the leds is the voltage required for them to work so this is the voltage they use.
Transistor 1 = 0.05v
Transistor2 = 0.05v
With the transisors reading 0.05v this is showing that they are fully open or fuly saturated.
Reflection
The only thing I would do differently next time would be to make sure I’m using the right resistor. I should have taken the resistor size down rather than up.
Finished Circuit
Circuit Design
