Open Source Voltage, Current, Power and Temperature logger

[AndrasH]

Deleted. Please delete the post.

[ledtester]

For battery operation it is nice to be able to shutdown or disconnect power from chips when they are not needed -- e.g. the display, SD card, etc.

Consider making it possible to use different MCU modules with the board. For instance, someone may want to use an ESP32 to offload the data via WiFi, Bluetooth, Zigbee, etc.

[2N3055]

IMHO, beware of feature creep.
2 ch are going to be limited use if they are not galvanically isolated from each other.
Low power is important. A month of battery time is good, longer is better, for standalone logger.
Like Ledtester said, do aggressive power shutdowns of components and processor peripherals and sleep modes for anything that is not used.
Making it USB-C charged would make for easy top up charging without interrupting logging and or simply power from the outside when power is available.
Do not rely on software for data exchange. You can do it if you want realtime reading, but that is not logger anymore..

Make it storage device that when you connect to PC it gives you disk with CSV log. Import to anything you want.

How will you configure it? Will you provide full UI on the device, or you will use a config software or even a config file (like XML for instance) that you can make simple app to create it from GUI. It can be python or even HTML page with Javascript. Both will be portable and not rely on OS.

Put enough buttons on it to make easy start/pause/stop logging on the spot where you are monitoring. What will you show on the screen? Draw a mockup.

My comments are here to show you that you need to define the target BEFORE you start designing.
What is exact use case?

You basically need to write a datasheet of imaginary device, and a mockup of user manual. While writing those, you will get many eureka moments, where you will remember "oh I need to provide Cancel button here too..".

Try it as a method. It might seem slow (we all like to start soldering as soon as possible) but it will give you refreshing clarity in what are you trying to accomplish. Design process proceeds organically from there.

My 2 c.....
Best,

[Swake]

This would be my workflow:
1/ List the use cases, only the must haves, anything else is a waste of time especially for the first version.
2/ Define the specs required to support the use cases. Think of all operational items such as how to power the device, durability, size of the case/box, portability, test leads, data exchange with the external world, long term support/warranty, software/firmware licenses, etc... Do not overspec it will only bring cost and difficulty.
3/ Check for existing open source projects that can meet the requirements, often something already exists or can be used as inspiration. Ideally you can reuse or contribute to that other project.
4/ Start the design. You might want to define multiple versions like basic and advanced.

Use case example: Monitor the voltage of a lead-acid vehicle battery (12V or 24V). Perform an action (send alert, close contact/relais) in case of rapid voltage drop or low state of charge. Device is powered from the lead-acid battery under test.