## 6 Communication between Battery and Charger via Bluetooth Module  
As an additional work, a Bluetooth module HC05 was added to the circuit to turn off the charger via a voice message from a smartphone--which is programmed by Arduio Uno--if all cells are fully charged and all cells are at a high level of charge and also turn on the charger if the cells are at a low voltage level. In order to control the charger via Bluetooth module, a mobile app \"BT Voice Control for Arduino\" is used. This app is available in the Google Play store. If a cell is high, it will be detected by the circuit at the end of each battery section transistor Q7 as shown in Figure 3 and if all cells are high it will be detected by transistor Q8 as shown in Figure 3. These transistors provide a signal to the analog pin of the microcontroller (Arduino) in order to turn off charging process. These detections are displayed by the LCD using the text \"all cells high\" or \"one cell is high\". It can also be observed by LED for each cell when the LED is turned on, it means this cell is at its high level. If one LED is not turned on it means that the cell is not high or it is damaged. The algorithm flowchart of smart monitoring is presented in Figure 11. Firstly, it detects if all cells are high, if it is true, it stops charging, if its not it continues to next stage. Next, if one cell is high it stops again charging, if it is not it countunes charging. Figure 10: (**a**) Cell voltages (fully charged) vs. time; (**b**) cell voltage (threshold voltage) vs. time. Figure 9: Cell voltage vs. balancing current of one cell. A picture of the testing layout is represented in Figure 12a. As can be seen in the figure, an LCD is expected to warn the user if one cell is higher than the desired voltage or if all cells are higher than this voltage. To avoid too much self-discharge by this feature, it can turn off itself after 10 days. If it draws \(<\)1 W for 10 days it is 0.24 kWh, which is reasonable. It also avoids that the battery stays at its maximum charge level when for some reason it is not used during the month. A picture of the testing layout with Bluetooth module is represented in Figure 12b. The state of charge of the cells is also detected by the microcontroller, so if all cells are at a high level of charge it automatically turns off the charger by sending a signal to the charger. It can be done both automatically by the microcontroller and also by voice message from the smartphone. The voice message can be generated by the smartphone with a mobile app \"AMR-Voice\", which is available in the Google Play store, then this message will be received by Bluetooth module HC05 which is connected to the Arduino, thus, the Arduino will disconnect the charger. In this paper, eight cells are considered, but the number of cells can be extended by adding more parts to the whole circuit, which are all the same and connected in series, but for simplicity, one circuit is shown in Figure 2.  
To monitor individual cell voltage, a new smart-monitoring system based on Bluetooth was made. The system provides users to monitor the cell voltages of the battery pack from a safe distance. The smart-monitoring system has played an important role during the last few decades [30; 31; 32]. The system was designed using the Arduino Nano as a microcontroller, a Bluetooth module (HC05), and a smartphone. This microcontroller is cheap and capable of measuring eight cell voltages by eight analog pins (A0-A7), which is suitable for our special purpose. Figure 11: Algorithm flowchart of the smart monitoring. Figure 12: (**a**) Printed circuit board (PCB) prototype of HVED; (**b**) PCB prototype of HVED with Bluetooth module. The Bluetooth module is HC05 which is a wireless device. To monitor the cell voltages, first, the individual cell voltages are measured by analog pins of Arduino Nano via isolated voltage probes, and then the data will be transmitted wirelessly by Bluetooth module to a new android application.