bigjosh · April 7, 2022 09:51 · Nov 7, 2014 · Nov 7, 2014 · Nov 7, 2014
diff --git a/NoPartsBatteryGauge.c b/NoPartsBatteryGauge.c
@@ -63,7 +63,7 @@ uint8_t readVccVoltage(void) {
 
 	// Enable ADC, set prescaller to /8 which will give a ADC clock of 1mHz/8 = 125kHz
 
-	ADCSRA |= _BV(ADEN) | _BV( ADSC) | _BV(ADPS1) | _BV(ADPS0);
+	ADCSRA = _BV(ADEN) | _BV(ADPS1) | _BV(ADPS0);
 
 	/*
 		After switching to internal voltage reference the ADC requires a settling time of 1ms before
@@ -72,17 +72,11 @@ uint8_t readVccVoltage(void) {
 	*/
 
 	_delay_ms(1);
-
 
 	/*
 		The first conversion after switching voltage source may be inaccurate, and the user is advised to discard this result.
 	*/
 
-	ADCSRA |= _BV(ADSC);				// Start 1st conversion
-
-	while( ADCSRA & _BV( ADSC) ) ;		// Wait for 1st conversion to be ready...	
-
-	// Start a Conversion			
 
 	ADCSRA |= _BV(ADSC);				// Start a conversion
 

diff --git a/NoPartsBatteryGauge.c b/NoPartsBatteryGauge.c
@@ -47,7 +47,7 @@ time and an initial system clock prescaling of 8, resulting in 1.0 MHz system cl
 // For faster readings, you could initialize once, and then take multiple fast readings, just make sure to
 // disable the ADC before going to sleep so you don't waste power. 
 
-uint16_t readVccVoltage(void) {
+uint8_t readVccVoltage(void) {
 
 	// Select ADC inputs
 	// bit    76543210 
@@ -108,9 +108,9 @@ uint16_t readVccVoltage(void) {
 
 	// Compute a fixed point with 1 decimal place (i.e. 5v= 50)
 	//
-	// Vcc    =  (1.1v * 1024) / ADC
-	// Vcc100 = ((1.1v * 1024) / ADC ) * 10				->convert to 1 decimal fixed point
-	// Vcc100 = ((11   * 1024) / ADC )					->simplify to all 16-bit integer math
+	// Vcc   =  (1.1v * 1024) / ADC
+	// Vcc10 = ((1.1v * 1024) / ADC ) * 10				->convert to 1 decimal fixed point
+	// Vcc10 = ((11   * 1024) / ADC )				->simplify to all 16-bit integer math
 
 	uint8_t vccx10 = (uint8_t) ( (11 * 1024) / adc); 
 

diff --git a/NoPartsBatteryGauge.c b/NoPartsBatteryGauge.c
@@ -0,0 +1,166 @@
+/*
+ * NoPartsBatteryGuageAVR.c
+ *
+ * This is a simplified demonstration of how to detect power supply voltage by using the on chip 
+ * analog-to-digital converter to measure the voltage of the internal band-gap reference voltage. 
+ *
+ * The code will read the current power supply voltage, and then blink an LED attached to pin 6 (PA7). 
+ *
+ * 1 blink  = 1 volts <= Vcc < 2 volts	(only applicable on low voltage parts like ATTINY84AV)
+ * 2 blinks = 2 volts <= Vcc < 3 volts 
+ * 2 blinks = 2 volts <= Vcc < 3 volts
+ * 3 blinks = 3 volts <= Vcc < 4 volts
+ * 4 blinks = 4 volts <= Vcc < 5 volts
+ * 5 blinks = 5 volts <= Vcc  
+ *
+ * 0 blinks = power supply turned off :) 
+ *
+ * This code was tested on an ATTINY84A with default fuse settings, but should work unchanged on 
+ * any ATTINYx4 or ATTINYx4A, and should be easily ported to any 8-bit AVR with ADC and internal 1.1 reference voltage.
+ *
+ * More info at...
+ *
+ * http://wp.josh.com/2014/11/06/battery-fuel-guage-with-zero-parts-and-zero-pins-on-avr/
+ *
+ */ 
+
+
+//Comments in slash/asterisk form are quoted from the datasheet
+
+/*
+The device is shipped with CKSEL = “0010”, SUT = “10”, and CKDIV8 programmed. The default
+clock source setting is therefore the Internal Oscillator running at 8.0 MHz with longest start-up
+time and an initial system clock prescaling of 8, resulting in 1.0 MHz system clock.
+*/
+
+#define F_CPU 1000000
+
+#include <avr/io.h>
+#include <util/delay.h>
+
+
+// Returns the current Vcc voltage as a fixed point number with 1 implied decimal places, i.e.
+// 50 = 5 volts, 25 = 2.5 volts,  19 = 1.9 volts
+//
+// On each reading we: enable the ADC, take the measurement, and then disable the ADC for power savings.
+// This takes >1ms becuase the internal reference voltage must stabilize each time the ADC is enabled.
+// For faster readings, you could initialize once, and then take multiple fast readings, just make sure to
+// disable the ADC before going to sleep so you don't waste power. 
+
+uint16_t readVccVoltage(void) {
+
+	// Select ADC inputs
+	// bit    76543210 
+	// REFS = 00       = Vcc used as Vref
+	// MUX  =   100001 = Single ended, 1.1V (Internal Ref) as Vin
+
+	ADMUX = 0b00100001;
+
+	/*
+	By default, the successive approximation circuitry requires an input clock frequency between 50
+	kHz and 200 kHz to get maximum resolution.
+	*/	
+
+	// Enable ADC, set prescaller to /8 which will give a ADC clock of 1mHz/8 = 125kHz
+
+	ADCSRA |= _BV(ADEN) | _BV( ADSC) | _BV(ADPS1) | _BV(ADPS0);
+
+	/*
+		After switching to internal voltage reference the ADC requires a settling time of 1ms before
+		measurements are stable. Conversions starting before this may not be reliable. The ADC must
+		be enabled during the settling time.
+	*/
+
+	_delay_ms(1);
+
+
+	/*
+		The first conversion after switching voltage source may be inaccurate, and the user is advised to discard this result.
+	*/
+
+	ADCSRA |= _BV(ADSC);				// Start 1st conversion
+
+	while( ADCSRA & _BV( ADSC) ) ;		// Wait for 1st conversion to be ready...	
+
+	// Start a Conversion			
+
+	ADCSRA |= _BV(ADSC);				// Start a conversion
+
+
+	while( ADCSRA & _BV( ADSC) ) ;		// Wait for 1st conversion to be ready...
+										//..and ignore the result
+
+
+	/*
+		After the conversion is complete (ADIF is high), the conversion result can be found in the ADC
+		Result Registers (ADCL, ADCH).		
+		
+		When an ADC conversion is complete, the result is found in these two registers.
+		When ADCL is read, the ADC Data Register is not updated until ADCH is read.		
+	*/
+
+	// Note we could have used ADLAR left adjust mode and then only needed to read a single byte here
+
+	uint8_t low  = ADCL;
+	uint8_t high = ADCH;
+
+	uint16_t adc = (high << 8) | low;		// 0<= result <=1023
+
+	// Compute a fixed point with 1 decimal place (i.e. 5v= 50)
+	//
+	// Vcc    =  (1.1v * 1024) / ADC
+	// Vcc100 = ((1.1v * 1024) / ADC ) * 10				->convert to 1 decimal fixed point
+	// Vcc100 = ((11   * 1024) / ADC )					->simplify to all 16-bit integer math
+
+	uint8_t vccx10 = (uint8_t) ( (11 * 1024) / adc); 
+
+	/*	
+		Note that the ADC will not automatically be turned off when entering other sleep modes than Idle
+		mode and ADC Noise Reduction mode. The user is advised to write zero to ADEN before entering such
+		sleep modes to avoid excessive power consumption.
+	*/
+
+	ADCSRA &= ~_BV( ADEN );			// Disable ADC to save power
+
+	return( vccx10 );
+
+}
+
+
+int main(void)
+{
+
+	// Enable output for LED pin
+
+	DDRA |= _BV(PORTA7);
+
+
+    while(1)
+    {
+
+		// Read the current Vcc voltage as a 2 decimal fixed point value
+
+		uint8_t vccx10 = readVccVoltage();
+
+		// Convert to whole integer value (rounds down)
+
+		uint8_t vcc = vccx10 / 10;
+
+		// Indicate the Vcc voltage by blinking the LED Vcc times...
+
+		for(int i=0;i<vcc;i++) {	
+
+			PORTA |= _BV(PORTA7);		// Turn on LED
+
+			_delay_ms(250);
+
+			PORTA &= ~_BV(PORTA7);		// LED off
+
+			_delay_ms(250);			
+
+		}
+
+		_delay_ms(1000);			// Pause before next round
+
+	}
+}