Sunday, November 14, 2010

Oxygen Sensor Tester Circuit Board Write-Up

Regan's Oxygen Sensor Tester Circuit Board Write-Up

Component List: 
  • 9V1 Zener Diode, IzRm 5.6mA
  • 2x 0.1uF Capacitor
  • 3x 1N4001 Diode
  • 14 Pin LM324AN Integrated Circuit
  • Red, Green, and Yellow Led's (1.8V, 9.5mA)
  • R2, R3 and R4 = 1K
  • R5 = 390R
  • R6 = 10K
  • R7 = 270R
  • R8 = 470R
  • Jumper Wires
  • Veroboard, 16x25 Holes

R2= (12V - 0.7V- 1.8V) / 0.0095A= 1K

R3= (12V-0.7V -0.7V- 1.8 ) / 0.0095A= 1K

R4= (12V - 0.7V- 1.8V) / 0.0095A = 1K

R5= (12 - 9.1) / 0.0095A = 305Ω = 390R   

R6 = 10K (Specs from Circuit Diagram)

R7 = (0.23V) / 0.00091A = 252Ω = 270R

R8 = (0.63 - 0.23V) / 0.00091A = 440Ω = 470R

What It Does?
This circuit's purpose is to act as an oxygen sensor tester, not an actual oxygen sensor.

How It Works? 
A 12V supply is connected to the 12V positive wire, the current flows through a protection diode and a capacitor, in order to filter the voltage into a smoother flow. The zener resistor (R5) limits the current flowing to the zener diode, which regulates the voltage down to 9.1 volts. Current for the various inputs of the Integrated Circuit is then further limited by the resistors R6, R7 and R8. Also 0V is connected to the negative lead which is connected to earth via R7 and the IC’s pin 11. After R5, pin 4 on the IC is connected to the 12V positive rail. The sensor input is connected to a supply of 0 to 1V which represents an actual oxygen sensor output range. A low voltage of 0.01V will cause the red LED to light up, if a higher voltage of 0.3V is detected by the oxygen sensor tester then the green LED will light up and when an even higher voltage of 0.4 - 0.5V is detected the yellow LED will light up, and finally when a high voltage of 0.6 to 0.9 is detected the red LED lights up. 
Testing Procedure: To test this circuit you will need to connect a 12V supply to the 12V positive wire and then the 0V negative wire to earth. At the same time a variable supply of 0 - 1V is to be connected to the supply wire, and again the earth to the 0V negative wire. The LED's will emit light in relation to the variable voltage you have placed upon the circuit.

Faults: I had to make two attempts at this circuit. My first attempt taken had many faults come along with it. All three of my diodes did not have drillings under them as they ran along the same track. My yellow LED had shorted after multiple times of taking out and putting back in the LED. Pin 10 and 13 were not connected as they should have been, also Pins 6 and 9 were not connected. I put a drill hole under the Integrated Circuit (IC) which seperated pins 6 and 9 when I should not have, I then had to connect these two points by means of a jumper wire. One track was bridged to another due to a solder fault. I simply resoldered that point to remove the bridged connection made. My red LED was the wrong way round. My Cathode leg should have been facing toward the IC. This was easily replaced by taking out and placing the Cathode at the correct point. After all of these faults occured my circuit was still not running. My green LED lit up and then at 0.1V it switched off and the yellow LED came on but only slightly. My red LED never lit up. All of these mistakes gave me a good understanding of what can be done to avoid these faults from occuring. I began from scratch and redesigned a second Sensor Tester, taking into account all my faults and mistakes from before. I constructed my new Sensor Tester and it worked straight away with no faults. The need not to change any components resulted in a tidy finished board.

Reflection: My first at this circuit resulted in a numerous amount of faults which in the end left me with a messy looking board. Although my first attempt at this board was not useless, infact it was extremely helpful. My experience's from my first Sensor Tester allowed me to identify the possible faults that were to occur, and also how to avoid them for next time. This was proven correct by my second attempt at this circuit where no faults were encountered and it made for a clean looking Oxygen Sensor Tester.

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