Week 4, 3 Sep

I was told by Roshan to work on the output circuit of the prototype. The prototype is an armband version of Internet Pajama, whereby it consists of only 1 air pump. This prototype is mainly to demonstrate the feasibility of the system, and the correctness of design.

So, I started off by designing the schematic diagram. This includes reading through all components' datasheets and wire up all the components together. My goal is to make the circuit as small as possible, thus MAX1760 is used for step up voltage converter.
MAX1760

max1760

I need to implement 2 power supply circuits, which are 5V and 3.3V. For both power supplies, the input voltage will be 2.4V, and step up voltage converters are used to get our desired voltage levels.

A DC voltage of -3.3V is needed for the amplifier to get working. Thus, MAX1673 is used as a voltage inverter.
MAX1673

max1673

For microcontroller, PIC16F76 is chosen. This is because it is small in size, and yet its functions are sufficient.
PIC16F76

pic16f76

A buffer is needed so that the output voltage is sufficient to turn on the transistor controlling the air pump. So, CD4050BCN is used here.
CD4050BCN

cd4050bcn

For pressure sensor, I use MPX10GS. It is a low-cost pressure sensor which can sense up to 10kPa.
MPX10GS

mpx10gs

Because the sensor voltage from the sensor itself is in the range of microvolts to milivolts, an amplifier is needed. In this case, AD620AN Low Cost Low Power Instrumentation Amplifier is used. I set the gain of amplifer to be around 10 to 100 so as to amplify the small signals from sensor itself, and feed it to PIC for comparison.
AD620AN

ad620an

Below is the complete design of schematic diagram, a rough draft I would say. Changes may be needed when I work on the firmware of PIC.

OutputCircuit
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