From 8f22c2e8525120b51c3c967c8467d5a14b30f1fb Mon Sep 17 00:00:00 2001
From: Kenneth Barbour <kenbarbour@gmail.com>
Date: Tue, 16 Jun 2020 20:32:41 -0400
Subject: [PATCH] added a rough mapping of voltage to percent

---
 src/battery.h | 16 ++++++++++++++++
 src/web.cpp   |  5 +++--
 2 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/src/battery.h b/src/battery.h
index 771c90c..916f7ef 100644
--- a/src/battery.h
+++ b/src/battery.h
@@ -6,6 +6,8 @@
 const int BATT_IN_PIN = A0;
 const int BATTERY_CHECK_INTERVAL = 5000;
 
+const double BATTERY_PERCENT_MAP[] = {3.2, 3.6, 3.65, 3.7, 3.75, 3.85, 4.9, 4.0, 4.1, 4.15, 4.2};
+
 typedef struct battery_info_t
 {
     uint last_raw = 0;
@@ -21,6 +23,20 @@ float battery_get_voltage()
     return (float) Battery.last_raw * .00042;
 }
 
+unsigned int battery_get_percent()
+{
+    float v = battery_get_voltage();
+    int i = 0;  // find the index of the first map element higher than v
+    if (v >= BATTERY_PERCENT_MAP[10]) return 100;
+    while (BATTERY_PERCENT_MAP[i] <= v) i++;
+    if (i == 0) return 0;
+
+    float a = v - BATTERY_PERCENT_MAP[i-1];
+    float b = BATTERY_PERCENT_MAP[i] - BATTERY_PERCENT_MAP[i-1];
+    float c = a / b * 10;
+    return (i-1) * 10 + c;
+}
+
 void uweather_handle_battery()
 {
     unsigned long now = millis();
diff --git a/src/web.cpp b/src/web.cpp
index 43b088c..58db67d 100644
--- a/src/web.cpp
+++ b/src/web.cpp
@@ -88,12 +88,13 @@ void handle_weather_current(HttpRequest& req, HttpResponse& res)
   dtostrf(battery_get_voltage(), 2, 1, buff[3]);
   Serial.printf("temp= %s, pres= %s, hum=%s\r\n", buff[0], buff[1], buff[2]);
   res.headers.set("Content-Type", "application/json");
-  content.printf("{\"time\": null, \"temperature\": %s, \"pressure\": %s, \"humidity\": %s, \"battery\": { \"voltage\": %s, \"is_charging\": %s}}",
+  content.printf("{\"time\": null, \"temperature\": %s, \"pressure\": %s, \"humidity\": %s, \"battery\": { \"voltage\": %s, \"is_charging\": %s, \"percent\": %d}}",
       buff[0], 
       buff[1], 
       buff[2],
       buff[3],
-      (Battery.is_charging ? "true":"false")
+      (Battery.is_charging ? "true":"false"),
+      battery_get_percent()
     );
 }