R5 = 338ohm resistor
R6 = 10K ohm resistor
R7 = 270 ohm resistor
R8 = 460ohm resistor
R2 = 1k ohm resistor
R3 = 1k ohm resistor
R4 = 1kohm resistor
D1 = 9.1v zener diode
D2 = 1N4001 Diode
D3 = 1N4001 Diode
C1 = 0.1uF capasitor
C2 = 0.1uF capasitor
LED1 = red 3mm L.E.D
LED5 = yellow 3mm L.E.D
LED6 = green 3mm L.E.D
Caculations I used to work out resistors in this O2 sensor circuit
.63 / .23 = 2.7
9.1 - .63 = 8.47
9.1 - .23 = 8.87
Rt = 10000 * 9.1 / 8.47 = 10744 - 10000 = 744
744/2.7 = 275ohm
744 - 275 = 469ohm
(12 - 1.8)/0.0095 = 1073ohm
(12-1.8 - .7)/0.0095 = 1000ohm
Problems encoutered
There was a problem I encoutered with this circuit when I built it was when I introduced 12 supply to it, the red led would not light up, after testing the led I discovered that the led was not connected to the circuit and after looking into the problem some more found that I had cut the track in the wrong position sepirating the led and resistor from the ic chip.
Another problem i encountered was when I introducted the 12v supply the green and red led would light up, after looking at my design for a while i discovered that i had a mix up in my design and had put the green led and yellow led in the wrong posistion, due to this I had a few components also in the wrong posistion. This problem was quickly fixed. After rectifying these two problems the circuit worked perfectly and without problmes.
Test procedure
To test this circuit I connected it to a 12v supply voltage, when this happens the red Led should light up because there is no input signal. Then I needed to use a voltage regulator made by kirill to test the circuit in more depth, when changing the input voltage the leds should change, this is due to the change in input signal the leds respond.
After testing the circuit I took voltage drop reading across the omponents.
R5 = 1.93v
R6 = 9.03v
R7 = .24v
R8 = .42v
D1 = .47v
D2 = .71v
C1 = 11.65v
C2 = .45v
LED1 = 1.93v
LED5 = 1.77v
LED6 = 1.29v
Reflection
The only thing I would do differently next time would be to check my design more carefully frist time around, if I did this this time I would have avoided all the problems that I had.
