Android Multimeter Premium 2.0.0
In the new version of multimeter 2.0.0 you can find new functions such as serial monitor and possibility of communication via USB cable (OTG connection) or Bluetooth. You can use the circuit of the previous versions but if you want to use USB connection (OTG cable) you will have to upload the sketch with the version of code 2.0.0. At the moment you will only have to upload the sketch and you will not have to make any modifications to be able to use the circuit of the previous version. But if you want to use both connections with the same sketch 2.0.0 you will have to connect Rx pin and Tx pin of the bluetooth module to the Rx and Tx pins of the arduino. The Rx pin of the bluetooth module must be connected to the Tx pin of the arduino and the Tx pin of the bluetooth module to the Rx of the arduino. The sketch with the lower version of 2.0.0 can not use USB connection. To use USB connection your smartphone must have that option (not all smartphones support this mode of connection, although today most smartphone support it).
At the moment I tried arduino uno, arduino nano and ESP32. To be able to connect our arduino to the smartphone we will need an OTG cable as you can see in the image below. Do not forget: in the menu you must choose USB connection.
After uploading the sketch 2.0.0 and connecting the OTG cable you can use the multimeter without the need for a bluetooth module.