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- /*
- * adc.c
- *
- * Copyright (c) 2024 Thomas Buck (thomas@xythobuz.de)
- *
- * This program is free software: you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation, either version 3 of the License, or
- * (at your option) any later version.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
- * GNU General Public License for more details.
- *
- * See <http://www.gnu.org/licenses/>.
- */
-
- #include <stdio.h>
- #include <math.h>
- #include "pico/stdlib.h"
- #include "hardware/adc.h"
-
- #include "adc.h"
-
- #define LIPO_USE_PERCENTAGE_CURVE
-
- #define ADC_NUM 2
- #define ADC_PIN (26 + ADC_NUM)
-
- #define ADC_VREF 3.3
- #define ADC_RANGE (1 << 12)
- #define ADC_CONVERT (ADC_VREF / (ADC_RANGE - 1))
-
- #define BAT_R1 10000.0f
- #define BAT_R2 18000.0f
-
- #define FILTER_OLD 0.999f
- #define FILTER_NEW (1.0f - FILTER_OLD)
-
- #ifndef LIPO_USE_PERCENTAGE_CURVE
- static const float full_battery = 4.1f;
- static const float empty_battery = 3.2f;
- #endif // ! LIPO_USE_PERCENTAGE_CURVE
-
- static float filtered = 0.0f;
-
- static float bat_read(void) {
- float v_adc = adc_read() * ADC_CONVERT;
-
- // Vadc = Vbat * R2 / (R1 + R2)
- float v_bat = v_adc / (BAT_R2 / (BAT_R1 + BAT_R2));
- return v_bat;
- }
-
- void bat_init(void) {
- adc_init();
- adc_gpio_init( ADC_PIN);
- adc_select_input( ADC_NUM);
- filtered = bat_read();
- }
-
- float bat_get(void) {
- filtered = (filtered * FILTER_OLD) + (bat_read() * FILTER_NEW);
- return filtered;
- }
-
- float bat_to_percent(float voltage) {
- float percentage = 0.0f;
-
- #ifdef LIPO_USE_PERCENTAGE_CURVE
- /*
- * Try to linearize the LiPo discharge curve.
- * https://electronics.stackexchange.com/a/551667
- *
- * Seems to work relatively well, although
- * "stopping" at 3.5V feels a bit high to me.
- */
- percentage = 123.0f - (123.0f / powf(1.0f + powf(voltage / 3.7f, 80.0f), 0.165f));
- #else // LIPO_USE_PERCENTAGE_CURVE
- percentage = 100.0f * ((voltage - empty_battery) / (full_battery - empty_battery));
- #endif // LIPO_USE_PERCENTAGE_CURVE
-
- return MIN(MAX(percentage, 0.0f), 100.0f);
- }
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