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The output result is probably grossly exaggerated, but this should be appropriate enough to form a comparison with the filtered signal output.
Common Mode filters
One possible solution to this problem is using a common mode filter, by taking two wires and removing voltages that a common between then, it can be used as a way of elimination EMI. So far two types of common mode filters are tested: Differential Amplifier, and bypass capacitors.
Differential Amplifier
With the use of a differential amplifier, the signals that common to both inputs (V1 and V2) can be suppressed from the output Vout while the difference between V2 and V1 are amplified. In this case we only want to eliminate noise that are induced in our signal wires, if R1=R2, Rf=Rg and the op-amp is ideal, the theoretical output follows the equation: Vout=Rf/R1*(V2-V1).
By setting R1=R2=Rf=Rg, we will have a unity gain amplifier and thus have Vout=V2-V1. We can make use this feature to eliminate EMI by taking two wires and only passing the signal voltage on one of the wires. By inducing EMI on the two wires, they can be suppressed by the unity gain amplifier and have only have our desired signal on Vout.
Testing setup
Using a Texas Instruments TLV314 op-amp, the unity-gain amplifier was configured using 2.2M resistors with Rout being a 10M resistor. The Op-amp was powered using 3.3V and -3.3V sources respectively. The oscilloscope is probed across Rout.What is not shown in the image is that the function generator's output is wrapped around the long "Signal" wire to act as our EMI source. We desire the EMI to be induced equally along the two wires.
I also tested the amplifier using 100k resistors and with 0.1uf capacitors coupling the Vsig inputs to GND.
Before I began the measurements, I tested the approximate resonant frequency of the long wire to see at which frequency will the highest Vpk-pk will be induced into the long wire. The function generator was set to a sine wave with 20Vpk-pk output with output load set to High-Z. While these measurements are perhaps over-exaggerated compared to more practical measurements, but it does help minimize other uncontrollable noise factors such as 120V AC noise. For now this will be considered the worst case scenario. From what I found a 27 MHz frequency gave me the highest Vpk-pk that was induced onto the "signal" wire.
Additionally, the 3.3v "signal" was connected to Vsig+. This will represent our signal which should show up in our Vout.
Measurements
With 2.2M resistors
Unfiltered
Filtered
WIth 100k Resistors
Unfiltered
Filtered
With 100k Resistors + decoupling capacitors to GND
Unfiltered
The screenshot appears to be missing. But its measured Vpk-pk was 7.5Vpk-pk
Filtered
Bypass Capacitors
This circuit also makes use of the difference between two voltages. The noise that is induced into both Vin+ and Vin- will be shorted to the GND by the capacitors, additionally, any voltages common to both Vin- and Vin+ will be cancelled out at Vout if the voltage is measured about the resistor. It should be noted however that this GND is an Earth GND, which is separate from the common reference GND.
The Setup
In this setup Rout=10M and the capcitance for the bypass capacitors are 0.1 uF. A 3.3v "signal" is passed into Vin+ with EMI induced onto both Vin+ and Vin- wires. The oscilloscope was placed across Rout (Not shown in diagram). The Earth GND was connected to the green "Earth" terminal on the power supply.
Measurements
Unfiltered
Filtered
Results
Setup | Measured Frequency (MHz) | Unfiltered Vpk-pk | Filtered Vpk-pk | Suppression factor ([Unfiltered Vpk-pk]/[Filtered Vpk-pk]) |
|---|---|---|---|---|
| Unity Amplifier (2.2M Resistors) | 27 | 7.44 | 2.16 | 3.44 |
| Unity Amplifier (100k Resistors) | 7.44 | 1.20 | 6.2 | |
| Unity Amplifier (100k Resistors + 0.1uf decoupling capacitors) | 7.5 | 2.56 | 2.93 | |
| Bypass Capacitors only (0.1uF Capacitors) | 5.92 | 3.04 | 1.95 |
Button Debouncing
Abstract
Switches are not prefect components. Sometimes they "bounce" and their state will not be a single transition from one to the other, but transition multiple times before settling to the new state. This is undesired as they are unpredictable and can cause incorrect readings into our driver input. Thus the objective is the measure the behavior of the button bouncing and develop hardware solutions that will prevent the button readings from bouncing. Software solutions will not be a focus for now.
The Setup
Two types of switches will be used for the measurements: a button switch and a toggle switch. As the basis for the measurements, we will first measure the unfiltered button signal. The schematic shows the initial setup:
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The capacitor used in this circuit is a 10000Pf capacitor:
Measurements
Circuit 1: Unfiltered Switches
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