The problem of the separation of the power supplies also arrived as regards the loading of the software in the memory of the Attiny controller.

To program Attiny microcontroller I used the Arduino as isp programmer, realized by Arduino Uno board.

But how to connect the programmer (signals powered by the Arduino UNO 5v supplied by the PC USB) with the Attiny microcontroller powered by the lithium cell?

How to separate the power supplies?

To solve this question I decided to carry out a hardware separation by means of jumpers connected to 2 connectors:

Connectors inserted = battery power supply

Connectors removed = it is possible to connect the programmer isolated from the battery

This technical solution, in addition to allowing the software upgrade without removing the module from the cell, also allows you to:

- remove power from the module (recommended during installation and removal of the module)

- perform a hardware reset of the module, avoiding the installation of the reset button