CIRCUIT BOARD 3

COMPONENTS: Resistors x7 carbon film, R2,R3,R4= 1kohms, R5= 380ohms, R6= 10kohms, R7= 260ohms, R8= 470ohms. Quad op-amp. L.E.D x3- LED1 red, LED5 yellow, LED6 green. all 1.8volts. Rectifing diodes x3, D2,D3,D4 1N4001. Zener diode- D1= 9V1. Capacitors x2 C2,C1= 0.1uF. 12v supply. sensor input= 0-1volt

CALCULATIONS: I=V/R= 8.47/10000= 0.000847amps. R=V/I. R8= .4/.000847= 472.2ohms. R7= .23/.000847= 271.5ohms. R6= 10kohms. R5= 2.2/.0056= 392.8ohms. R4= 9.5/.0095= 1000ohms. R3= 8.8/.0095= 926.3ohms. R2= 9.5/.0095= 1000ohms

HOW THE CIRCUIT WORKS: As the supply voltage comes through it powers the op-amp and goes to the zener where you could say is regulated down to 9.1volts and the other 2.9v charge and store in the capacitor. The 9.1volts then go down through R6,R8,R7 and voltage is divided because of the different size resistors. The voltage at points between these resistors go to the op-amp at there specific points. This is so when the sensor input changes between 0-1volt the op-amp will non-invert and invert amplify causing different LEDs to light up and turn off.

TESTING: We know by the diagram what voltage should be at certain points. I used available voltage to test for these known voltages and also to find out if I had any open circuits. Also I did some voltage drop testing to make sure components weren't high in resistance or open or shorted circuits.
Test 1 my board didnt work. All LEDs were on when only the red LED should of.
Test1: RESULTS: VD- R2, R3, R4 9.5v, 8.8v, 9.5v. LED1, 5, 6 2.03v, 3.66v, 1.29v.
Test2 my board still didnt work but this time the zener was earthed to the common ground.
Test3 my board finally worked.
Test 3: RESULTS: When the sensor input was .91v LED1 Vd= 2.05volts, LED5, 6 Vd= 0volts. sensor input .41v LED5 Vd= 3.91volts, LED1, 6 Vd= 0volts. sensor input .12v LED6 Vd= 2.62volts, LED1, 5 Vd= 0volts.

PROBLEMS: I had many problems with my board. My first problem I come across was I never earthed the zener to common earth. I solved this problem when I tested for available voltage and found 12.3v before the zener and 0v after, but i should have got around 3v. My second problem was only the red LED was lighting up, and changing the input signal still didnt change a thing. I tested available voltage with 12Vs and no input signal. I found I had the correct voltage readings at the specific points, this meant that the problem was in the op-amp. But I had diode tested it at the start and it was fine. I ended diode testing it again and found circuits were shorted together. I then scraped the board so the circuits werent shorting any more. Then I set it up for testing again and it finally worked.

If I had the chance to do the circuit board again I would triple check everything. The soldering, the earth (all of them), the power to the op-amp and earth from the op-amp, and diode test close wires and make sure they're not shorting to each other.