Internal resistance meter - low quality version

I've been interested in internal resistance meters for a long time, but I didn't have a strong need for them. Plus, my skills weren't great, so I only worked on one so far with poor results, and then I gave up. Every now and then, I'd get interested again, and then I'd think, "What's the harm in playing around?" So I started working on them again and studied the internal resistance meter circuit by [yjmwxwx](https://oshwhub.com/yjmwxwx). Later, while playing with bridges and tweezers, I saw Piao Zong's internal resistance meter circuit. They're actually quite similar, so I just modified Piao Zong's circuit.
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The main controller chosen is the STM32F103RC, which is relatively expensive. However, I got a bunch of these from an old POS machine through a scam, so it cost me nothing. The GD32 tested fine, and other compatible chips should also work.

Resistance settings are two-level automatic: 0-150mΩ and 0-3Ω. Voltage range is 0-100V (not yet implemented in software). Actually, because the internal resistance hasn't been stabilized, other voltage settings, UI, calibration, etc., are all unimplemented. Updates will be slow, taking years. I didn't originally intend to open-source it, but then I thought, what if some expert insists on optimizing the software? (Dream on!)
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The casing was directly generated from LCSC EDA and 3D printed using a monkey
! ![IMG_20240417_155057.jpg] [Image 1] Three buttons: the rightmost one is the power button; the other two functions are undetermined. There's an upgrade button (boot0) on the back, with upgrade method SWD + serial port
. [Image 2] Currently uncalibrated; test results show a 0.5mΩ drift (

previously measured by scraping the EVE code), and a test result of 13.52mΩ
. [Image 3] Another section shows 13.48mΩ
. [Image 4] A 14500 from a disassembled counterfeit mouse; test result shows 95.
[Image 5] A 10mΩ sampling resistor; test result shows 10.41
. [Image 6] 30mΩ test result: 30.33
![IMG_20240417_154454.jpg] 60mΩ test result: 60.16
![IMG_20240417_154513.jpg]
The current performance is terrible; treat it as a toy. If you really want to use it properly, go for the TS457 or HIOKI.

Temporary code
: https://gitee.com/feixiangjusha/internal-resistance-meter.git