9. Input Devices: Noah, Andrew, Kathryn¶
Our assignment is to probe an input device(s)’s analog levels and digital signals.
Work Distribution¶
| Assignment | Name |
|---|---|
| Noah | Analog Device |
| Kathryn | Digital Device |
| Andrew |
Analog Signal - Noah¶
For an analog input device, I used a thermistor setup to act as a voltage divider. A thermistor is a resistor that changes resistance based on temperature. A voltage divider is a circuit that takes an input voltage, and splits that circuit into 2 paths based on the quotient of 2 resistors. The formula for a voltage divider is Vout = Vin * (R2 / (R1 + R2)). In our case, the vin was 3.3v, and the vout was any number between 0 and 3.3v, with lower meaning a higher temperature.
Analog PCB design - Noah¶
as our lab only had surface mount thermistors, I designed a small circuit consisting of 3 pads, that being vin, vout, and ground, and 2 resistors, a standard 10k resistor and a thermistor that maxed out at 10k ohms. This board was designed to be used with a 1/32in bit to mill faster, and was designed to use pads instead of through hole for interfacing
After milling the board, I soldered a 10k resistor to the left side, closer to the vin pad, and a thermistor to the right side, closer to the ground. I also soldered on the wires, a red for Vin, white for Vout, and black for ground
Multimeter Testing - Noah¶
The groups assignment was the probe the output level of a input with some logic analyzer. As this temperature sensor is really simple and analog, a Logic analyzer wouldn’t be good for it, and as its VERY simple, we didn’t need to use an oscilloscope. In order to test the device, We measured the voltage between it and ground, which, because the resistance changes based on temperature, would also cause the voltage to change based on temperature. In this case, as temperature went up, voltage also went up. We could test with the multimeter either on the connected wires or on the board itself, both being shown below
*Everything was tested at 3.33v here
It can be probed either by placing the probes right onto the board
or probing the signal plate and power plate
The ambient temperature in the room was around 22 celsius, and gave a voltage of 1.581
Just by breathing, heating it up, the voltage increase by .1
A strong thing about this sensor is its range. It’s not that accurate for small ranges, but you could put this in a kiln and (providing you have some magic solder joints) it would be able to work the entire time.
Analog Code - Noah¶
On top of that, we also used the ADC on a esp32-c3 to measure it. The most important feature of the chip for measuring an analog signal is the resolution of its ADC, or analog to digital converter. The esp32-c3 is very strong for this, with a 12 bit (4096 levels). This is the same as the pi pico, but 4x better than the arduino uno’s 10 bit (1024 level) resolution. Because of the increased adc resolution, the sensor is able to detect 4x more steps (4x the quality) in temperature vs the uno.
*Everything was tested at 3.30v here
As seen in the video, as my bodyheat, which is hotter than the ambient temperature touches the sensor, the themistor increases its resistance therefore routing more voltage to the Vout pin.
TTP223 Digital Signal¶
I used the XIAO ESP32C3 end of this board to control a TTP223 touch sensor.
As usual, I first checked to make sure that the touch sensor was working. In the code, if the touchState is HIGH, which is what it should be if touched, serial monitor outputs “Touched: 1.” If not, it’s “Not touched: 0.” That is what happened, so I went forward with measurement.
I used a multimeter to measure the digital signals. I toggled it onto the first node to the right of the OFF button, the one that measures voltage in volts. I had the COM port (the black one) plugged into COM and the red plug on VΩHz. The black plug touches GND and the red one touches output.
Here is a video of what it read.
As you can see, when I touched the sensor, it went high to around 3.3V which is the VCC pin the sensor was connected to. When I stopped touching it, the voltage went back down to 0, low.