From 8bf93bfd50113ec09ec5cb231634527569c50c20 Mon Sep 17 00:00:00 2001
From: Sadeep Madurange <sadeep@asciimx.com>
Date: Sun, 17 Aug 2025 11:34:04 +0800
Subject: Use 1.1V reference voltage.

---
 main.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

(limited to 'main.c')

diff --git a/main.c b/main.c
index a16101d..ddf8f42 100644
--- a/main.c
+++ b/main.c
@@ -100,11 +100,11 @@ static inline void flash_led(void)
 	}
 }
 
-static inline uint16_t get_bat_volt(void)
+static inline uint16_t getbat(void)
 {
 	uint16_t vbg;
 
-	ADMUX |= (1 << REFS0);
+	ADMUX |= (1 << REFS1) | (1 << REFS0);
 	ADCSRA |= (1 << ADEN) | (1 << ADPS2) | (1 << ADPS1); /* clk: 50-200 kHz */
 
 	// https://www.sciencetronics.com/greenphotons/?p=1521
@@ -115,11 +115,11 @@ static inline uint16_t get_bat_volt(void)
 		; 
 
 	ADCSRA &= ~(1 << ADEN);
-	vbg = 3300UL / 1024 * ADC
-
+	vbg = (1100UL * ADC) / 1024;
 	ADCSRA &= ~(1 << ADEN);
 
-	return vbg * 3;
+	// 56k/10k voltage divider
+	return (vbg * 66) / 10;
 }
 
 int main(void)
-- 
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