Microchip Technology

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  • Battery Fuel Gauge

  • Created: Jan 09, 2017

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This reference design is a circuit that determines the total consumed fuels in the battery and also its remaining available fuels. It calculates the voltage and the current that is charging into or discharging from a battery and is displayed to an LCD display. The design is mainly built around the MCP3421 ADC devices, MCP73831 battery charger, and a PIC18F4550 MCU.

The circuit requires a 9V power supply to provide power to its active components, which includes the MCU, ADC and battery charger devices. The user could connect either a 9V battery or a 9V supply through the DC adapter. When the board is powered, the user could connect a battery to be measured. When JP1 jumper is connected, a battery-discharging path from the battery to the current sensor to the 100Ω resistor (R11) to ground is created. This simulates how battery fuel is consumed in real applications. The differential input pins of U1 (ADC) are connected across the current sensor and measure the current passing through the current sensor. The ADC can determine whether the measured current is discharging current or charging current by testing the sign of the current value. The data from the ADC is communicated to the PIC18F4550 MCU. The calculation of the battery voltage, discharging current and consumed fuel takes place in the MCU and is displayed to the LCD. The measurement takes places approximately every one-second and updates the measurement data and calculated results on the LCD for about every second.

A buzzer is included in the circuit, which beeps during start-up, when the battery is used more than 50% of its initial value and when the battery is connected. A potentiometer is also available for calibration of the ADC input voltage. If the user finds the battery voltage reading in the LCD suspicious, he can connect a voltmeter between the battery and ground then adjust the potentiometer until the readings on the LCD and voltmeter are the same.



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