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hc_sr04: Improve accuracy by measuring micro-seconds

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This commit is contained in:
Clashlab 2023-02-27 09:19:30 +01:00
parent 0f8d7dd6db
commit 4439a83733
1 changed files with 13 additions and 14 deletions
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27
applications/plugins/hc_sr04/hc_sr04.c
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@ -3,6 +3,7 @@
// Ported and modified by @xMasterX // Ported and modified by @xMasterX
#include <furi.h> #include <furi.h>
#include <furi_hal.h>
#include <furi_hal_power.h> #include <furi_hal_power.h>
#include <furi_hal_console.h> #include <furi_hal_console.h>
#include <gui/gui.h> #include <gui/gui.h>
@ -26,7 +27,7 @@ typedef struct {
NotificationApp* notification; NotificationApp* notification;
bool have_5v; bool have_5v;
bool measurement_made; bool measurement_made;
uint32_t echo; // ms uint32_t echo; // us
float distance; // meters float distance; // meters
} PluginState; } PluginState;
@ -72,7 +73,7 @@ static void render_callback(Canvas* const canvas, void* ctx) {
FuriString* str_buf; FuriString* str_buf;
str_buf = furi_string_alloc(); str_buf = furi_string_alloc();
furi_string_printf(str_buf, "Echo: %ld ms", plugin_state->echo); furi_string_printf(str_buf, "Echo: %ld us", plugin_state->echo);
canvas_draw_str_aligned( canvas_draw_str_aligned(
canvas, 8, 38, AlignLeft, AlignTop, furi_string_get_cstr(str_buf)); canvas, 8, 38, AlignLeft, AlignTop, furi_string_get_cstr(str_buf));
@ -110,9 +111,11 @@ static void hc_sr04_state_init(PluginState* const plugin_state) {
} }
} }
float hc_sr04_ms_to_m(uint32_t ms) { float hc_sr04_us_to_m(uint32_t us) {
const float speed_sound_m_per_s = 343.0f; //speed of sound for 20°C, 50% relative humidity
const float time_s = ms / 1e3f; //331.3 + 20 * 0.606 + 50 * 0.0124 = 0.034404
const float speed_sound_m_per_s = 344.04f;
const float time_s = us / 1e6f;
const float total_dist = time_s * speed_sound_m_per_s; const float total_dist = time_s * speed_sound_m_per_s;
return total_dist / 2.0f; return total_dist / 2.0f;
} }
@ -147,10 +150,6 @@ static void hc_sr04_measure(PluginState* const plugin_state) {
furi_delay_ms(10); furi_delay_ms(10);
furi_hal_gpio_write(&gpio_usart_tx, false); furi_hal_gpio_write(&gpio_usart_tx, false);
// TODO change from furi_get_tick(), which returns ms,
// to DWT->CYCCNT, which is a more precise counter with
// us precision (see furi_hal_cortex_delay_us)
const uint32_t start = furi_get_tick(); const uint32_t start = furi_get_tick();
while(furi_get_tick() - start < timeout_ms && furi_hal_gpio_read(&gpio_usart_rx)) while(furi_get_tick() - start < timeout_ms && furi_hal_gpio_read(&gpio_usart_rx))
@ -158,16 +157,16 @@ static void hc_sr04_measure(PluginState* const plugin_state) {
while(furi_get_tick() - start < timeout_ms && !furi_hal_gpio_read(&gpio_usart_rx)) while(furi_get_tick() - start < timeout_ms && !furi_hal_gpio_read(&gpio_usart_rx))
; ;
const uint32_t pulse_start = furi_get_tick(); const uint32_t pulse_start = DWT->CYCCNT;
while(furi_get_tick() - start < timeout_ms && furi_hal_gpio_read(&gpio_usart_rx)) while(furi_get_tick() - start < timeout_ms && furi_hal_gpio_read(&gpio_usart_rx))
; ;
const uint32_t pulse_end = DWT->CYCCNT;
const uint32_t pulse_end = furi_get_tick();
//FURI_CRITICAL_EXIT(); //FURI_CRITICAL_EXIT();
plugin_state->echo = pulse_end - pulse_start; plugin_state->echo = (pulse_end - pulse_start) / furi_hal_cortex_instructions_per_microsecond();
plugin_state->distance = hc_sr04_ms_to_m(pulse_end - pulse_start); plugin_state->distance = hc_sr04_us_to_m(plugin_state->echo);
plugin_state->measurement_made = true; plugin_state->measurement_made = true;
//furi_hal_light_set(LightRed, 0x00); //furi_hal_light_set(LightRed, 0x00);
@ -270,4 +269,4 @@ int32_t hc_sr04_app() {
delete_mutex(&state_mutex); delete_mutex(&state_mutex);
return 0; return 0;
} }