flipper-zero-tutorials/gpio/hc_sr04

HC_SR04

Description

The original version is from SquachWare hc_sr04.

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.