ECE 110/120 Honors Lab Section : Week 7

Characterization of the pressure sensor:

We are going to use the pressure sensor in a voltage divider circuit. When no one is sitting on the bike, the pressure sensor would give a very high resistance and the output voltage should be 0V. When there is someone sitting on the bike, the pressure sensor would give a lower resistance and the output voltage should be 5V. Based on these, I have drawn a schematic for our voltage divider circuit (shown below). Now we will try to figure out what resistance is appropriate for the fixed resistance. 

To calculate the fixed resistor's value, I am going to build a voltage divider circuit powered by a 5V Arduino. I programmed the Arduino to read the voltage across R2 in analog (0 to 1023). For an output voltage of 0V, we should expect a reading closer to 0 and for an output voltage of 5V, we should expect a reading closer to 1023. We should also try to avoid having any values that in very close to the middle as that might leave the circuit undefined. 

Test cases we are going to use: 

1) Press pressure sensor with full force of thumb

2) Press pressure sensor with full force of palm (hand)

3) Sit on the pressure sensor

4) No pressure applied at all

We should expect the output voltage to be 5V for all expect the last case. I am going to start off with a fixed resistor at 45 M Ohms. This value has been roughly estimated based on the readings we got across the resistor (look at week 6 for values). 

-- to be continued –