Assemble it with completely off the shelf parts
Most aspiring hobbyists don't have a full SMT workstation. I didn't when I started out. I only had a crappy soldering iron. However you can also substitute modules here for off the shelf parts so that you can throw together a kit on a breadboard.
The caveat is that the overall build will be bigger. I have included the parts that can substitute each module below.
1. Soldering iron (optional)
2. A phone or gatttool to see the data.
Connect wires from the voltage or current measurement outputs. When the device is powered, the MCU will automatically start measuring voltages and pushing the converted values to the Bluetooth chip. The converted values are in the format "[voltage_1],[voltage_2],[current_1],[current_2]"
Manufacture the board and solder the components on. If you prefer, you can also breadboard it.
The JDY-08/HM-11 forms the wireless core of this project. It is an extremely cheap (<$2) Bluetooth BLE module that already has a complete set of AT-like commands preprogrammed. The key usefulness of this module is that it already has a transparent mode included as part of the application, which allows us to send arbitary sets of data to and from the IC.
To make it easily programmable, is paired with ATMega-328P, the 'Arduino' chip. This also means that you don't need a special board to use it. Simply use it as a shield for an Arduino Uno, wire it to a Teensy, or build your own board as I have done here.
Alternatively, use SiLab's Laser Bee MCU that is specifically designed to collect analog data and work at 3.3V.
To make it usable and safe, it can take either an AA rechargeable or standard alkaline non-rechargeable battery. I think this provides better flexibility in power options - you can get batteries at a gas station, but it is unlikely you can do the same with a LiPo. I use a single battery here to minimize bulk, with a step-up voltage boost regulator to get it to 3.3V for the MCU and Wireless device.
Additional advanced functionality includes:
1. uA current measurement
2. Sleep mode
4. Graphing App
5. Record data in App (in development)
6. Pin toggling (in development)
To retrieve data very simple. simply use nRF connect app to scan for "JDY-" device. Once connected, first service will output the data from the wireless measurement.
If you really want the data collection to be remote, you can also use a Raspberry Pi 4's Bluetooth to scan and connect to the device. That way you can SSH in to grab the data.
You can also use the dedicated App to scan for and connect to devices, which will then display and graph the information from each of the terminals.
1. This device is mainly used for measuring low-power wireless devices (3.3V). It can measure high currents and voltages, but would need modifications to the existing circuitry to do so. For high voltages, you'll need to create a voltage divider circuit in front of the input.
2. It doesn't have a noise rejection circuit