EMI Interference

Abstract

   With our current plan of transmitting data over long wire, the possibility arises that they are susceptible to noise generated by Electromagnetic Interference. Since our solar car will be running 4 hi-power brush less motors, their huge AC power spikes can induce heavy amounts of noise into our system. This introduced noise can wreck havoc into our wires, causing data loss and/or inaccurate sensor measurements.Thus this objective is to measure the effects of EMI and determine ways to eliminate it from our system.

The setup

    Our experimental setup follows: an arbitrary voltage DC source that acts as our "signal" is connected on one end of a long wire. We then induce an EMI on the long wire and measure the voltage output from the other end of the long wire. The following image shows the setup on breadboard:  

The "signal" source is a basic DC power supply that will supply 3.3V to our long wire. This will function as an equivalent of a digital "high" signal. A 2.2M resistor is placed in series with the long wire the limit the current that passes through the wire, this will simulate the signal line.

The oscilloscope probe is placed on the node connecting the long wire and the 2.2M resistor. This will measure the resulting "signal" after it traveled over long wire.

To induce the EMI, another wire is wrapped around the long "signal" wire. It is then connected to the output of a function generator. I should be noted that this wire is left floating and it is not connected to anything else but the function generator output. By providing and AC voltage to the output of the function generator, the change in voltage will induce current into the long "signal" wire. The purpose of wrapping the wire is the maximize the induction of current onto the long signal wire.

On the function generator, the output was set to a 16 MHz 10Vpp sine wave with the output load set to high-Z. The image shows the following output parameters:

Measurements

Without the interference applied, by turning off the output of the function generator, the image shows the measurement from the oscilloscope. The DC power supply is on and set to 3.3V output.

 This will form as our basis for the measurements.

The output from the function generator is also measured. This was achieved by attaching a 2.2M resistor in series with the function generator output and probing the voltage across the resistor with the oscilloscope. The image shows the resulting waveform:

The measured Vpk-pk is not exactly 20Vpk-pk as desired, but this error is not significant for the analysis.

With the EMI applied to the long "signal" wire, the measured output follows:

The output result is probably grossly exaggerated, but this should be appropriate enough to form a comparison with the filtered signal output.