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Improved accuracy for hc_sr04 ultrasonic device!

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This commit is contained in:
Derek Jamison 2023-02-23 13:02:23 -05:00
parent 2d35562eeb
commit 31c9be7ef7
2 changed files with 49 additions and 20 deletions
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26
gpio/hc_sr04/README.md
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@ -1,4 +1,26 @@
## Original version from: [SquachWare hc_sr04](https://github.com/skizzophrenic/SquachWare-CFW/tree/dev/applications/plugins/hc_sr04)
# HC_SR04
## Description
The original version is from [SquachWare hc_sr04](https://github.com/skizzophrenic/SquachWare-CFW/tree/dev/applications/plugins/hc_sr04).
## (5V -> VCC) / (GND -> GND) / (13|TX -> Trig) / (14|RX -> Echo)
This version modifies the code to use furi_hal_cortex_timer_get(0) to
obtain a high precision counter. We also tune the calculations based on measured observations. The display shows 2 digits after the decimal point, displaying in both cm and inches.
## Pins
- (Flipper -> HC_SR04 device)
- (5V -> VCC)
- (GND -> GND)
- (13|TX -> Trig)
- (14|RX -> Echo)
## Code changes
- #include <furi_hal_cortex.h>
- This has the definitions for FuriHalCortexTimer and furi_hal_cortex_timer_get(...)
- FuriHalCortexTimer beginTimer = furi_hal_cortex_timer_get(0);
- This gets the current time in beginTimer.start.
- The offset is 0 (we could use offset ).
- furi_string_printf(str_buf, "Distance: %0.2f cm", (double)plugin_state->distance);
- This rounds the output to the nearest hundredths place.
- hc_sr04_duration_to_cm(...)
- I have no idea why total_dist needs to be multiplied by 1.588, but doing so seems to make all of the measurements correct.
- The code overhead, delays in IN/OUT, etc. seem to take the same time as sound tranvelling for 0.497 cm there and back; so we add this fixed constant. If you Flipper was faster/slower you would need to adjust this constant.

43
gpio/hc_sr04/hc_sr04.c
View File

@ -5,6 +5,7 @@
#include <furi.h>
#include <furi_hal_power.h>
#include <furi_hal_console.h>
#include <furi_hal_cortex.h>
#include <gui/gui.h>
#include <input/input.h>
#include <stdlib.h>
@ -26,8 +27,8 @@ typedef struct {
NotificationApp* notification;
bool have_5v;
bool measurement_made;
uint32_t echo; // ms
float distance; // meters
uint32_t echo; // us
float distance; // cm
} PluginState;
const NotificationSequence sequence_done = {
@ -68,15 +69,16 @@ static void render_callback(Canvas* const canvas, void* ctx) {
elements_multiline_text_aligned(
canvas, 64, 40, AlignCenter, AlignTop, "13/TX -> Trig\n14/RX -> Echo");
} else {
elements_multiline_text_aligned(canvas, 4, 28, AlignLeft, AlignTop, "Readout:");
FuriString* str_buf;
str_buf = furi_string_alloc();
furi_string_printf(str_buf, "Echo: %ld ms", plugin_state->echo);
furi_string_printf(str_buf, "Echo: %0.2f ms", (double)(plugin_state->echo/1000.0f));
canvas_draw_str_aligned(
canvas, 8, 28, AlignLeft, AlignTop, furi_string_get_cstr(str_buf));
furi_string_printf(str_buf, "Distance: %0.2f cm", (double)plugin_state->distance);
canvas_draw_str_aligned(
canvas, 8, 38, AlignLeft, AlignTop, furi_string_get_cstr(str_buf));
furi_string_printf(str_buf, "Distance: %02f m", (double)plugin_state->distance);
furi_string_printf(str_buf, "Distance: %0.2f in", (double)(plugin_state->distance/2.54f));
canvas_draw_str_aligned(
canvas, 8, 48, AlignLeft, AlignTop, furi_string_get_cstr(str_buf));
@ -110,11 +112,17 @@ static void hc_sr04_state_init(PluginState* const plugin_state) {
}
}
float hc_sr04_ms_to_m(uint32_t ms) {
uint32_t hc_sr04_duration_to_usActual(uint32_t duration) {
return duration * 1.5888f / 1e2f;
}
float hc_sr04_duration_to_cm(uint32_t duration) {
const float speed_sound_m_per_s = 343.0f;
const float time_s = ms / 1e3f;
const float total_dist = time_s * speed_sound_m_per_s;
return total_dist / 2.0f;
duration *= 1.588f; // calculated by measurement.
const float time_one_way_sec = duration / 2e6f;
float total_dist = time_one_way_sec * speed_sound_m_per_s;
total_dist += 0.497f; // offset for fixed delays.
return total_dist;
}
static void hc_sr04_measure(PluginState* const plugin_state) {
@ -147,10 +155,6 @@ static void hc_sr04_measure(PluginState* const plugin_state) {
furi_delay_ms(10);
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();
while(furi_get_tick() - start < timeout_ms && furi_hal_gpio_read(&gpio_usart_rx))
@ -158,16 +162,19 @@ static void hc_sr04_measure(PluginState* const plugin_state) {
while(furi_get_tick() - start < timeout_ms && !furi_hal_gpio_read(&gpio_usart_rx))
;
const uint32_t pulse_start = furi_get_tick();
FuriHalCortexTimer beginTimer = furi_hal_cortex_timer_get(0);
while(furi_get_tick() - start < timeout_ms && furi_hal_gpio_read(&gpio_usart_rx))
;
const uint32_t pulse_end = furi_get_tick();
FuriHalCortexTimer endTimer = furi_hal_cortex_timer_get(0);
//FURI_CRITICAL_EXIT();
plugin_state->echo = pulse_end - pulse_start;
plugin_state->distance = hc_sr04_ms_to_m(pulse_end - pulse_start);
uint32_t duration = endTimer.start - beginTimer.start;
plugin_state->echo = hc_sr04_duration_to_usActual(duration);
plugin_state->distance = hc_sr04_duration_to_cm(duration);
plugin_state->measurement_made = true;
//furi_hal_light_set(LightRed, 0x00);