First you should disassemble your logger and check out the model of MCU. Two out of four boards I examined had STM32L152 low-power MCU, one had Atsam4S16b MCU and one had Atsam4S4b MCU. Atsams are more powerful, but official debuggers are expensive, so I shelved those boards for further experiments.

If you know about some affordable way of programming Atsam MCUs, please share your ideas in the comments.

If you are lucky enough and have a board with STM32 MCU, it might be possible to use a cheap ST-Link dongle to program it. It’s what I’m going to do.

On some boards you might find other usable items, like flash and EEPROM memory chips. Please check out the attached pictures.

Do it only when the board is powered off! Remove the battery even if you think it is worn-out.

I decided to start with Q-tag logger because it had thru-hole pads for standard pin headers, and I assumed they must had been designed for debugging purpose. To detect which is which, you’ll need a multimeter set to continuity mode and a datasheet for your MCU. This one is for STM32L152. Touch gently MCU's pin and a pad on the PCB with your probes to detect whether they are connected. At least you’ll need to detect VCC3.3V, GND, SWDIO and SWDCLK pads to be able to program the microcontroller.

I have attached the pictures with my layouts, but I don’t guarantee that your board would have the same design. So I encourage you to test it yourself.

If you have a Q-tag board with thru-hole pads, you could just use standard headers. If you have surface-mount pads, like on Temptale boards, use thin wires.

Connect 3.3V, GND, SWDIO and SWDCLK pins to your programmer. For the first connection test I suggest that you use an official ST-LINK utility. Connect your programmer to USB port and press “Connect to the target” button. If everything is ok, you should be able to see data from your microcontroller.

When you are sure that everything works, you may install STM32CubeIDE or configure an opensource development environment. Now you have an affordable development board, and it’s up to you to decide how to use it. Maybe it might be possible to port Arduino to it and implement a USB bootloader or build some customized HID device.