Building a Low Pressure Sensor for Pasco Capstone
Welcome to the Low Pressure Sensor for Pasco Capstone project page hosted by Walla Walla University. This project was developed and is maintained by Dr. Tom Ekkens. If you have comments or suggestions please send email to tom.ekkens@wallawalla.edu. This page was last updated on March 13, 2024.
Some years ago, Pasco sold a Low-Pressure Sensor (CI-6534) for the Science Workshop 750. That design has been retired and replaced by a high pressure sensor. If the high precision of the low pressure sensor is needed, an similar part to the CI-6534 can be constructed using the following process.
The Electrical Design
The electrical system consists of a MPX10GP (JP3) chip to do the actual pressure to voltage conversion and four amplifiers to get the voltage scaled to what the Science Workshop expects. While all four amplifiers can be used on a TL074 chip, slightly better results are obtained using the AD620AN (IC2) amplifier for the sensitive signals and the TL074 (IC1) amplifiers for everything else. Power is supplied by the Science Workshop through the 8 pin DIN connector (JP1).
The board file (Click for file) was sent out for fabrication since it is a two-sided board. The picture of the board is shown below. Both amplifier chips were socketed so they can be changed if necessary. This design has one major construction issue. The fourth quad (pins 12- 14) isn’t used but the space is needed to get to the AD620 pins so the schematic shows the pins connection. During build, those three pins are removed from the socket so the unused quad doesn’t see strange signals.
The 3D-Printed Case
The case for the low-pressure sensor circuit board is based off the May 2022 box for the Type-K sensors. It is printed from black PLA with a 60% fill. The case is held together by four ½” #2 sheet metal screws from the bottom. The middle two support legs are not screwed in since the force from student use is not on the circuit board. The sensor on the circuit board is connected to the quick release port by a 28mm length of vinyl tubing. ¼” OD by 0.170” ID is the easiest tube to use but it doesn’t seal the ends as good as ¼” OD by 1/8” ID. The finished product is shown below.
