Testing Noise on Steering Interface Board

Measuring resistance setup:

• Inserting steering interface board in the car, with a cable connecting to ground, and another to AIN1 (the input for Cruise Control Speed)
• Connecting a multimeter to both cables, to see the differences in resistance for each state on the Cruise Control Setting
• Following Data measured:

Test 1:

Test 2:

Measuring the resistance after populating R4 with a 3.9k resistor:

• The following are the values received:

Measuring voltage setup:

• Adding a 3.9K resistor to R4 on the circuit, as well as adding a red cable to 3V0 that will connect to the power supply. Testing with everything else similar to the last circuit, except connecting the power supply to same ground as in the circuit.
• Measuring the voltages with the multimeter, after turning on the power supply and setting it to 5 Volts.
• The following data was received:

Switching from AIN1 to AIN3 (from cruise control speed to signal from steering stalk)

• The reason for changing was due to the unexpected differences in voltage (were supposed to be around 5, 2.5 and 0).
• Moved the 3.9K resistor to populate R2 and to connected to the circuit for AIN3. Moved the input cable from node in AIN1 circuit to spot in AIn3 at R6.
• The following voltages were measured with the same power supply setup providing 5 volts

Finally, connecting an oscilloscope to the circuit to see the peak to peak difference in potential (Vpp)

• This was done by connecting the positive terminal to the input cable that connected to AIN3
• The power supply was still connected providing 5 volts
• The oscilloscope was on normal mode, and was reading for Vpp and Vavg (Note: Vavg read were the same as in the above table).
• The following data was read:
  Vpp (neutral mode):  80mV

Note: The value of 80 mV becomes extremely high when a walkie talkie signal was tested right beside the circuit. It ranged from 1V-3V, and therefore proved the magnitude of influence in noise.

Walkie off:

Walkie on

Next, to test noise reduction, the circuit was rebuilt with the same 3.9k ohm resistor, except connected to the cruise control F/B(soft) with ribbon cable insulated by an aluminum shield. This itself was tested in a similar layout as the with the uninsulated tests, with the oscilloscope and power supply connected similarly.

The wave shown on the oscilloscope remained affected by the noise of the walkie talkie connected to it.

The next step was to test the insulated wires with a first order low pass filter connected to the input from the board.

Components:

• TL074 op amp
• Resistors
• Capacitor
• Bread board
  

Basic schematic:

The resulting readings on the oscilloscope displayed reduced noise from the walkie talkie signals.

Walkie off:

Walkie on:

(A bit farther from cable’s exposed ends)

(A bit closer to cable’s exposed ends)

Conclusion:

The only way to effectively reduce EMI is by using aluminum shielded wires while connecting it to a first order low pass filter.