Week 7, 1 Oct

After CA1, I heeded Dr. Cheok's advice and focus on my output circuit part by part.

I tested part by part on breadboard. To begin with, I started off with the buffer. That's pretty easy. The output voltage depends on the power supply of the buffer. Since the buffer is used to turn the MOSFETs on or off, I realise we can actually use 3.3V instead of 5V as stated in the previous design. So I decided to change it to 3.3V.

Next, I worked on the amplifier part. With a single resistor of 5.1k Ohm, the amplifier is able to give a gain of 10. Nevertheless, it is kind of noisy so I think I have to give it a big enough ground plane and it will be fine.


Then, I continued to test out the air pressure sensor. The output voltage is very low, so by feeding it into the amplifier, I applied different voltages to the motor to pump air into the air pressure sensor. The following data is obtained:

Voltage Applied / V Current / A Output Voltage / V
0.0 0.00 0.16
3.0 0.22 0.39
3.5 0.23 0.46
4.0 0.23 0.77
4.5 0.24 0.98
5.0 0.27 1.05

After plotting with excel, I got a graph which is not strictly linear but in some sense, have some degree of propotionality.


Maybe I can work out an equation to map the inputs to the output voltage in a more linear manner when i develop the firmware for PIC.

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