Cicuit board 3-O2 sensor tester

Component list.
One LM324 quad opamp.
LED red
LED yellow
LED green
3 diodes 1N4007
1 Zener diode 9.1v
Capacitor x2 0.1uF
R2=1000
R3=1000
R4=1000
R5=380
R6=10000
R7=270
R8=470

Calculations
To find R8 and R7
9.1-(.23+.63)=8.24
8.24/3=2.74
2.74+2.74=5.48
270 and 550 ohm. but i used 470 ohms

Technical explanation
This circuit tests the O2 sensor in your car which will ultimately tell you if your car is running rich or lean. The lower the voltage the leaner the car is.
When the Green LED is on:
The Green LED is on when there is under .23V coming from the signal going into the 12 input. As the input is smaller than the .23 going into the 13 input the ouput at 14 negative, which switches the Green LED on. The yellow and red LEDs are off as there is less than .23V.

When the Yellow LED is on:
The signal voltage is between .23V and .63V. The signal goes into the 9 and .23V goes into the 10. As the signal is higher than the input voltage the output is negative and acitvates the yellow LED. It does not activate the Red LED as the input voltage is higher there. And does not activate the Green as the input voltage is to high for it and so there outputs would be positive.

When the Red LED is on:
There is more than .63V from the signal going into the 6 input. As this is greater than the .63 voltage input, the output is negative which activates the Red LED. As the signal input is also at 3 and the input voltage at 2 the output is postive which flows through D3 down to the negative side of the yellow LED, this shorts the Yellow circuit causing it to not light up when the Red is lit up. The Green LED will not light up also as it is getting a positive output, but it needs a negative to work.
Voltage drop readings.

	Red is on .65V	Yellow is on .3V	Green is on .1V
Red LED	1.99	1.34	1.34
Yellow LED	1.70	1.97	1.10
Green LED	1.25	1.24	2.08
R2	8.64	0	0
R3	8.49	8.12	0
R4	0	0	8.68
R5	2.14	2.15	2.12
R6	8.50	8.51	8.49
R7	0.22	0.22	0.22
R8	0.38	0.38	0.38
D1	9.10	9.10	9.10
D2	0.69	0.70	0.69
D3	0.65	9.04	10.43
D4	0.50	0.69	0.05

Problems with the circuit:
The first problem I had with my first board was I didnt break the tracks properly, so when i first connected it to the tester I shorted out the tester and my board as there was a short directly from negative to positive. From there it was problem after problem. The Green LED circuit worked, but the Red and Yellow didnt. I found another short accross the red and yellow circuits. I think when the first short occured I think that i shorted D2 as both the Yellow and Red LED would come on together.
On my 2nd circuit, I redesigned my circuit to have a common signal and common negative so to simplify the design. The first attempt at building the 2nd board was a success.

If I were to redo this board again, I would simplify the circuit once again. I would also double check the board before connecting it to a power supply. As the first short is what destroyed my board.