Add an example to read VBUS and VSYS

The process is different on Pico and Pico W so demonstrate how to do it.

Fixes #324

Author: peterharperuk

adc/CMakeLists.txt

@@ -5,4 +5,5 @@ if (NOT PICO_NO_HARDWARE)
     add_subdirectory(joystick_display)
     add_subdirectory(onboard_temperature)
     add_subdirectory(microphone_adc)
+    add_subdirectory(read_vsys)
 endif ()

adc/read_vsys/CMakeLists.txt

@@ -0,0 +1,30 @@
+add_library(power_status_adc INTERFACE)
+target_sources(power_status_adc INTERFACE
+        ${CMAKE_CURRENT_LIST_DIR}/power_status.c
+        )
+target_include_directories(power_status_adc INTERFACE
+        ${CMAKE_CURRENT_LIST_DIR}
+        )
+target_link_libraries(power_status_adc INTERFACE
+        hardware_adc
+        hardware_gpio
+        )
+
+add_executable(read_vsys
+    read_vsys.c
+    )
+target_include_directories(read_vsys PRIVATE
+    ${CMAKE_CURRENT_LIST_DIR}
+    )
+target_link_libraries(read_vsys
+    pico_stdlib
+    power_status_adc
+    )
+if (PICO_CYW43_SUPPORTED)
+    target_link_libraries(read_vsys
+        pico_cyw43_arch_none
+    )
+endif()
+
+pico_add_extra_outputs(read_vsys)
+example_auto_set_url(read_vsys)

adc/read_vsys/power_status.c

@@ -0,0 +1,48 @@
+/**
+ * Copyright (c) 2023 Raspberry Pi (Trading) Ltd.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#include "stdbool.h"
+#include "hardware/adc.h"
+#include "power_status.h"
+
+#if CYW43_USES_VSYS_GPIO_PIN
+#include "pico/cyw43_arch.h"
+#endif
+
+// Get power status
+// Must have called adc_init
+// On Pico W must also have called cyw43_arch_init
+void power_status(bool *mains_powered, float *voltage_result) {
+#if defined CYW43_WL_GPIO_VBUS_PIN
+    *mains_powered = cyw43_arch_gpio_get(CYW43_WL_GPIO_VBUS_PIN);
+#elif defined PICO_VBUS_GPIO_PIN
+    gpio_set_function(PICO_VBUS_GPIO_PIN, GPIO_FUNC_SIO);
+    *mains_powered = gpio_get(PICO_VBUS_GPIO_PIN);
+#else
+    #error No vbus pin defined
+#endif
+
+#if CYW43_USES_VSYS_GPIO_PIN
+    cyw43_thread_enter();
+#endif
+
+    adc_gpio_init(PICO_VSYS_GPIO_PIN);
+    adc_select_input(PICO_VSYS_ADC_NUM);
+
+    uint16_t vsys = 0;
+    const int sample_count = 3;
+    for(int i = 0; i < sample_count; i++) {
+        vsys += adc_read();
+    }
+    vsys /= sample_count;
+
+#if CYW43_USES_VSYS_GPIO_PIN
+    cyw43_thread_exit();
+#endif
+
+    const float conversion_factor = 3.3f / (1 << 12);
+    *voltage_result = vsys * 3 * conversion_factor;
+}

adc/read_vsys/power_status.h

@@ -0,0 +1,21 @@
+/**
+ * Copyright (c) 2023 Raspberry Pi (Trading) Ltd.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#ifndef POWER_STATUS_H
+#define POWER_STATUS_H
+
+/*!
+ * \brief Get power status
+ *
+ * Returns whether mains or battery powered and the mains or battery voltage
+ * \note Must have called adc_init and on Pico W must also have called cyw43_arch_init
+ *
+ * \param mains_powered True if powered, False if running off a battery
+ * \param voltage Calculated voltage 
+ */
+void power_status(bool *mains_powered, float *voltage);
+
+#endif

adc/read_vsys/read_vsys.c

@@ -0,0 +1,74 @@
+/**
+ * Copyright (c) 2022 Raspberry Pi (Trading) Ltd.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#include <stdio.h>
+#include <pico/stdlib.h>
+#include <power_status.h>
+#include "hardware/adc.h"
+#include "pico/float.h"
+
+#if CYW43_USES_VSYS_GPIO_PIN
+#include "pico/cyw43_arch.h"
+#endif
+
+int main() {
+    stdio_init_all();
+
+    adc_init();
+    adc_set_temp_sensor_enabled(true);
+
+    // Pico W uses a CYW43 pin to get VBUS so we need to initialise it
+    #if CYW43_USES_VSYS_GPIO_PIN
+    if (cyw43_arch_init()) {
+        printf("failed to initialise\n");
+        return 1;
+    }
+    #endif
+
+    bool old_mains_power;
+    float old_voltage;
+
+    while(true) {
+
+        const float min_battery_volts = 3.0f;
+        const float max_battery_volts = 4.2f;
+
+        // Get power status
+        bool mains_power;
+        float voltage;
+        power_status(&mains_power, &voltage);
+        voltage = floorf(voltage * 100) / 100;
+
+        // Display power if it's changed
+        if (old_mains_power != mains_power || old_voltage != voltage) {
+            const char *power_str = mains_power ? "MAINS" : "BATTERY";
+            char percent_buf[10];
+            if (mains_power) {
+                percent_buf[0] = 0;
+            } else {
+                int percent_val = ((voltage - min_battery_volts) / (max_battery_volts - min_battery_volts)) * 100;
+                snprintf(percent_buf, sizeof(percent_buf), " (%d%%)", percent_val);
+            }
+
+            // Also get the temperature
+            adc_select_input(4);
+            const float conversionFactor = 3.3f / (1 << 12);
+            float adc = (float)adc_read() * conversionFactor;
+            float tempC = 27.0f - (adc - 0.706f) / 0.001721f;
+
+            // Display power and remember old vales
+            printf("Power %s, %.2fV%s, temp %.1f DegC\n", power_str, voltage, percent_buf, tempC);
+            old_mains_power = mains_power;
+            old_voltage = voltage;
+        }
+        sleep_ms(3000);
+    }
+
+#if CYW43_USES_VSYS_GPIO_PIN
+    cyw43_arch_deinit();
+#endif
+    return 0;
+}