Sometimes you’re just lucky. I have a project on my list for a long time. I have delayed this project for several months because I hate part of it – sensitive and high-precision analog measurement. Then, unexpectedly, I stumbled upon a completely correct trick, and my problem disappeared. Thank you, hacker network!
The project is a low vacuum regulator for “bagging” fiberglass laminates. What I need is some way to read the pressure sensor and turn on and off the vacuum pump accordingly. The industrial standard vacuum gauge is a neat device. In essence, it is a tiny strain gauge, which is located on the film between the vacuum side and the atmospheric side and encapsulated in a dime sized container. (this is a strain gauge, which is a sign, but I didn’t know it at that time.) I bought one for $15 15 15 years ago. It sat on my desk and waited for its analog circuit.
See, the MPX2100 operates at 12 volts and signals approximately 40 mV at the top of the 6-volt offset. This voltage level is inconvenient for the modern 3.3V microcontroller ADC. If I add a voltage divider to it, the resolution will be affected by the 6V signal. This means that some instrument amplifier circuits are combined to eliminate 6 volts and amplify 40 mV for the ADC. All the circuits I found on the Internet need a resistance value of 1%. I don’t have any. There are some special operational amplifiers. No fun, at least for me. So it’s right there.
Until I came across a project that used a part to cut a knife in the simulated jungle, and it happened to be a part of what I had in hand. Vacuum pressure sensor is a strain gauge, which is installed like a Wheatstone bridge, just like weighing with a load cell. What is the solution? A load cell ADC chip, hx711, can be found in every cheap scale or online, and the price is less than one dollar. The only other trick was to find a low-pressure pressure sensor to use it, but it turned out to be easy. I delivered one in two days.
In short, this project has dragged on for months, but as long as I have the right idea, I just need to click and weld for five minutes. If you are making millions of such devices, industrial applications and manufacturers’ application annotations are meaningful. In these devices, the one-time cost of making hard block prototypes is amortized, but the solution of hackers using weighing chips is only one-time. This shows just how useful it is to share our tips and Tricks – you won’t get that from the industry. Therefore, please send us your success stories and useful failures, and read more hackday every day!