Progress Report – Hall Transistor based Level Measure

Below you will find a progress report video. The video shows a demonstration of my work-in-progress project that I have mentioned, at least the 3D Print portion, in previous posts. The actual product is a powder level alerting system used in reloading. While reloading, if a case’s powder level is out of Tolerance, a beeper will sound. The firmware is written in C and C++ and while I am testing on an Arduino Nano the final product will be on a surface mounted ATTiny85. In fact all but two components on the circuit board will be surface mounted.

The only output on the device is a beeper and the only input is a single push-button. Despite this limitation I can change nine different settings based on the duration of the button press. The main body of the code uses a state machine with non-blocking code with the exception of routines that decode button presses and sound button press related beeps, which do use blocking subroutines.

I now consider the firmware to be complete. Next, I must start on the printed circuit board design and then fabrication. Once the product is finalized I will post an update. The entire product, both hardware and software, will be released open source when it is final. That is probably some months away.

By the way, I almost threw in the towel on this project because I could not get the hall effect transistor to be stable. After much frustration and, ultimately, a great deal of investigation, I discovered that the problem was that, during debugging, I was powering the Arduino device using a USB cable while also sending out debug serial ASCII text messages over the same cable. Apparently using serial data over the same USB cable that provides power was introducing sufficient noise to destabilize the hall effect transistor. Once my project switched over to a standalone power supply instead of using the USB cable, the hall effect transistor became stable. The final product will run off of a 1/2-AA battery. This bug should be of interest to anyone doing embedded system design – be careful about supplying serial data over the same cable that provides power.

 

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