Problem: The prototype experienced a battery outage (abnormal discharge) for a short period of time. After inspection, it was found that Bluetooth had a voltage of about 2.1V during sleep, causing the battery power to be consumed too quickly. Because the machine has a voice function, it requires a lot of current when playing voice. The machine is equipped with two Nanfu batteries, with a maximum voltage of about 3.2V. After about a week, the machine in operation became unresponsive and it was discovered that the battery was dead.
Troubleshooting:
1. First consider the circuit that powers Bluetooth. PNP transistors are used to control the power supply.
Transistor conduction principle: PNP transistor conducts at low voltage; NPN transistor conducts at high voltage.
Control Bluetooth power supply as follows:
One end of the transistor is connected to IO to control whether it is conductive, and the other two ends are connected to the Bluetooth power supply terminal BLE_VCC and the voltage VCC. The IO output is turned on at low voltage, Bluetooth gets the voltage, and Bluetooth is turned on. When closing, set IO to a high level and the transistor is turned off.
After inspection, there is no problem with the principle, code and transistor. However, when turning off Bluetooth and cutting off the transistor, BLE_VCC will have a voltage of 2.1V. This voltage consumes a lot of power and uses up my Nanfu battery.
2. Check whether the sleep mode is the serial port setting.
Use a multimeter to measure the RX and TX voltages of the serial port during sleep. It is found that the voltage of RX is about 2.8V, and the serial port is supplying power to the Bluetooth chip in the direction! ! !
Be sure to pull the serial port IO low during sleep.