From d516cd8a9eedfe0f4cd6c32e4526d6b0427ad338 Mon Sep 17 00:00:00 2001
From: pelgraine <140762863+pelgraine@users.noreply.github.com>
Date: Fri, 10 Apr 2026 14:25:51 +1000
Subject: [PATCH] =?UTF-8?q?Fixes=20#1183=20=E2=80=94=20T-Echo=20Lite=20inc?=
 =?UTF-8?q?orrect=20battery=20voltage?=
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Battery (TechoBoard.h/cpp): Added PIN_VBAT_MEAS_EN (P0.31) — the T-Echo
Lite has a gated voltage divider that must be enabled before reading. Also
added pinMode(PIN_VBAT_READ, INPUT) before each ADC read to reclaim P0.02
from other peripherals. Pin definitions hardcoded from LilyGo's
t_echo_lite_config.h.

I2C (variant.h): Corrected SDA/SCL from P0.04/P0.02 to P1.04/P1.02 per
LilyGo's IIC_1_SDA/IIC_1_SCL. The old P0.02 mapping conflicted with the
battery ADC pin.

GPS (variant.h): Corrected all five GPS pin assignments to match LilyGo's
config — UART TX/RX, wake, PPS, and power enable were all scrambled.

SPI (variant.h): Fixed SPI_INTERFACES_COUNT from _PINNUM(0, 2) to (2).

Tested on T-Echo Lite Non-Shell (USB-C, no display). Battery readings match
Heltec V4 reference within 10mV.
---
 variants/lilygo_techo_lite/TechoBoard.cpp | 43 +++++++++++++++++------
 variants/lilygo_techo_lite/TechoBoard.h   | 19 +++++-----
 variants/lilygo_techo_lite/variant.h      | 21 +++++------
 3 files changed, 53 insertions(+), 30 deletions(-)

diff --git a/variants/lilygo_techo_lite/TechoBoard.cpp b/variants/lilygo_techo_lite/TechoBoard.cpp
index 81d3d0c9..a11d31b2 100644
--- a/variants/lilygo_techo_lite/TechoBoard.cpp
+++ b/variants/lilygo_techo_lite/TechoBoard.cpp
@@ -8,24 +8,47 @@
 void TechoBoard::begin() {
   NRF52Board::begin();
 
+  // Configure battery measurement control BEFORE Wire.begin()
+  // to ensure P0.02 is not claimed by another peripheral
+  pinMode(PIN_VBAT_MEAS_EN, OUTPUT);
+  digitalWrite(PIN_VBAT_MEAS_EN, LOW);
+  pinMode(PIN_VBAT_READ, INPUT);
+
   Wire.begin();
 
   pinMode(SX126X_POWER_EN, OUTPUT);
   digitalWrite(SX126X_POWER_EN, HIGH);
-  delay(10);   // give sx1262 some time to power up
+  delay(10);
 }
 
 uint16_t TechoBoard::getBattMilliVolts() {
-  int adcvalue = 0;
-
+  // Use LilyGo's exact ADC configuration
   analogReference(AR_INTERNAL_3_0);
   analogReadResolution(12);
-  delay(10);
 
-  // ADC range is 0..3000mV and resolution is 12-bit (0..4095)
-  adcvalue = analogRead(PIN_VBAT_READ);
-  // Convert the raw value to compensated mv, taking the resistor-
-  // divider into account (providing the actual LIPO voltage)
-  return (uint16_t)((float)adcvalue * REAL_VBAT_MV_PER_LSB);
+  // Enable battery voltage divider (MOSFET gate on P0.31)
+  pinMode(PIN_VBAT_MEAS_EN, OUTPUT);
+  digitalWrite(PIN_VBAT_MEAS_EN, HIGH);
+
+  // Reclaim P0.02 for analog input (in case another peripheral touched it)
+  pinMode(PIN_VBAT_READ, INPUT);
+  delay(10);  // let divider + ADC settle
+
+  // Read and average (matching LilyGo's approach)
+  uint32_t sum = 0;
+  for (int i = 0; i < 8; i++) {
+    sum += analogRead(PIN_VBAT_READ);
+    delayMicroseconds(100);
+  }
+  uint16_t adc = sum / 8;
+
+  // Disable divider to save power
+  digitalWrite(PIN_VBAT_MEAS_EN, LOW);
+
+  // LilyGo's exact formula: adc * (3000.0 / 4096.0) * 2.0
+  // = adc * 0.73242188 * 2.0 = adc * 1.46484375
+  uint16_t millivolts = (uint16_t)((float)adc * (3000.0f / 4096.0f) * 2.0f);
+
+  return millivolts;
 }
-#endif
+#endif
\ No newline at end of file
diff --git a/variants/lilygo_techo_lite/TechoBoard.h b/variants/lilygo_techo_lite/TechoBoard.h
index fda393e7..7a43fd83 100644
--- a/variants/lilygo_techo_lite/TechoBoard.h
+++ b/variants/lilygo_techo_lite/TechoBoard.h
@@ -4,14 +4,12 @@
 #include <Arduino.h>
 #include <helpers/NRF52Board.h>
 
-// built-ins
-#define VBAT_MV_PER_LSB   (0.73242188F)   // 3.0V ADC range and 12-bit ADC resolution = 3000mV/4096
-
-#define VBAT_DIVIDER      (0.5F)          // 150K + 150K voltage divider on VBAT
-#define VBAT_DIVIDER_COMP (2.0F)          // Compensation factor for the VBAT divider
-
-#define PIN_VBAT_READ     (4)
-#define REAL_VBAT_MV_PER_LSB (VBAT_DIVIDER_COMP * VBAT_MV_PER_LSB)
+// ============================================================
+// T-Echo Lite battery pins — hardcoded from LilyGo t_echo_lite_config.h
+// NOT using any defines from variant.h for battery measurement
+// ============================================================
+#define PIN_VBAT_READ         _PINNUM(0, 2)   // BATTERY_ADC_DATA
+#define PIN_VBAT_MEAS_EN      _PINNUM(0, 31)  // BATTERY_MEASUREMENT_CONTROL
 
 class TechoBoard : public NRF52BoardDCDC {
 public:
@@ -20,10 +18,11 @@ public:
   uint16_t getBattMilliVolts() override;
 
   const char* getManufacturerName() const override {
-    return "LilyGo T-Echo";
+    return "LilyGo T-Echo Lite";
   }
 
   void powerOff() override {
+    digitalWrite(PIN_VBAT_MEAS_EN, LOW);
     #ifdef LED_RED
     digitalWrite(LED_RED, LOW);
     #endif
@@ -41,4 +40,4 @@ public:
     #endif
     sd_power_system_off();
   }
-};
+};
\ No newline at end of file
diff --git a/variants/lilygo_techo_lite/variant.h b/variants/lilygo_techo_lite/variant.h
index 16e0b5cb..07202165 100644
--- a/variants/lilygo_techo_lite/variant.h
+++ b/variants/lilygo_techo_lite/variant.h
@@ -24,7 +24,7 @@
 #define PIN_PWR_EN              _PINNUM(0, 30) // RT9080_EN
 
 #define BATTERY_PIN             _PINNUM(0, 2)
-#define ADC_MULTIPLIER          (4.90F)
+#define ADC_MULTIPLIER          (2.0F)
 
 #define ADC_RESOLUTION          (14)
 #define BATTERY_SENSE_RES       (12)
@@ -47,13 +47,13 @@
 ////////////////////////////////////////////////////////////////////////////////
 // I2C pin definition
 
-#define PIN_WIRE_SDA            _PINNUM(0, 4) // (SDA)
-#define PIN_WIRE_SCL            _PINNUM(0, 2) // (SCL)
+#define PIN_WIRE_SDA            _PINNUM(1, 4) // (SDA) - per LilyGo IIC_1_SDA
+#define PIN_WIRE_SCL            _PINNUM(1, 2) // (SCL) - per LilyGo IIC_1_SCL
 
 ////////////////////////////////////////////////////////////////////////////////
 // SPI pin definition
 
-#define SPI_INTERFACES_COUNT    _PINNUM(0, 2)
+#define SPI_INTERFACES_COUNT    (2)
 
 #define PIN_SPI_MISO            _PINNUM(0, 17) // (MISO)
 #define PIN_SPI_MOSI            _PINNUM(0, 15) // (MOSI)
@@ -149,10 +149,11 @@ extern const int SCK;
 #define PIN_DISPLAY_BUSY        DISP_BUSY
 
 ////////////////////////////////////////////////////////////////////////////////
-// GPS
+// GPS — per LilyGo t_echo_lite_config.h
+// PIN_GPS_TX/RX named from GPS module's perspective
 
-#define PIN_GPS_RX              _PINNUM(1, 13) // RXD
-#define PIN_GPS_TX              _PINNUM(1, 15) // TXD
-#define GPS_EN                  _PINNUM(1, 11) // POWER_RT9080_EN
-#define PIN_GPS_STANDBY         _PINNUM(1, 10)
-#define PIN_GPS_PPS             _PINNUM(0, 29) // 1PPS
+#define PIN_GPS_TX              _PINNUM(0, 29) // GPS UART TX → MCU RX
+#define PIN_GPS_RX              _PINNUM(1, 10) // GPS UART RX ← MCU TX
+#define GPS_EN                  _PINNUM(1, 11) // GPS RT9080 power enable
+#define PIN_GPS_STANDBY         _PINNUM(1, 13) // GPS wake-up
+#define PIN_GPS_PPS             _PINNUM(1, 15) // GPS 1PPS
\ No newline at end of file