Shared Projects by Bear_Metal

This is a small board to experiment with the STM32H503, a 250 MHz ARM Cortex-M33. The board will fit into a Arduino Nano socket, though it is only partially compatible with the Nano pinout. The KiCad project, BOM, and firmware are on GitHub. The firmware consists of a small command-line interpreter for testing boards, and uses the on-chip USB to communicate with a virtual terminal on your PC.

This board is centered around an STM32L412CB, which has a Cortex-M4 running at 80 MHz, 128K of flash, 40K of RAM, single precision FPU, USB FS Device, and a typical set of other peripherals.

The board is somewhat compatible with the STM32 Nucleo-32 boards, which are somewhat compatible with Arduino Nano. This is mainly so that I can use the Nano terminal blocks (https://www.amazon.com/gp/product/B095XVVGQ8).

The main purpose of the board is as a voltage/current logger for the study of battery charge/discharge curves. For this reason it has a large current sensing resistor connected to the L412’s op amp.

Another unique feature, for a board this size, is that it has an ETM Trace connector. This board works nicely with Segger’s J-Trace probe and Ozone debugger to provide instruction trace. The L412/L422 is the only STM32 Cortex-M4 (as far as I know) that has trace in a package smaller than 100 pins.

The KiCad schematic and pcb files are included in the download. All the parts are available from Digikey.

As of this writing I am bringing up basic software. I am also working on an update of the board to fix a couple minor bugs. I have not tried out the analog stuff yet.

I recommend Nefastor’s USB tutorial and STM32_VCP library:
https://nefastor.com/microcontrollers/stm32/usb/stm32cube-usb-device-library/usb-fundamentals/ https://github.com/Nefastor-Online/STM32_VCP

I followed the steps, wrote a little bit of my own code, and now I can use the L412’s native USB port as a virtual serial console, providing printf and getchar.

(experimental and as yet untested)

This is a differential buffer for connecting cheap voltmeters (for example: https://amazon.com/CenryKay-4-5-30v-Digital-Display-Voltmeter/dp/B08PB5NDMC) to the individual sticks of a Honda hybrid car’s IMA battery pack. The battery pack of a Honda hybrid car has 120 NiMH D-cells arranged in 20 sticks of 6 cells each. The cable running from the battery pack to the BCM (Battery Condition Monitor) has voltage sense taps for every two sticks. We tried attaching ten of the cheap voltmeters to these sense lines. The voltmeters have only two wires, which are used for both sensing the voltage and powering the meter. The problem is that it seems the taps are not tied directly to the battery – there must be some sort of current limiting resistor in each wire. The current drain of the voltmeters is enough that it changes the voltage read by the BCM, which throws a hissy fit and shuts down the hybrid assist system.

Here are some pictures from our first attempt: https://www.insightcentral.net/threads/yet-another-ima-problem-post.130739/page-2

This experiment uses a high impedance differential amplifier to read the voltage across each pair of sticks, and translate that to a ground referenced voltage with enough drive to run each voltmeter. The maximum voltage that might come out of the battery is less than 200 volts with respect to ground. The maximum differential across each pair of sticks is around 19 volts. The buffer that reads the highest stick pair might see inputs at full charge of 184 and 165, with a difference of 19 volts. With these inputs, the buffer would output 19 volts, referenced to vehicle ground, with a drive of around 25 ma to drive the voltmeter.