27 lines
1.3 KiB
Markdown
27 lines
1.3 KiB
Markdown
# HC_SR04
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## Description
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The original version is from [SquachWare hc_sr04](https://github.com/skizzophrenic/SquachWare-CFW/tree/dev/applications/plugins/hc_sr04).
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This version modifies the code to use furi_hal_cortex_timer_get(0) to
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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.
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## Pins
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- (Flipper -> HC_SR04 device)
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- (5V -> VCC)
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- (GND -> GND)
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- (13|TX -> Trig)
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- (14|RX -> Echo)
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## Code changes
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- #include <furi_hal_cortex.h>
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- This has the definitions for FuriHalCortexTimer and furi_hal_cortex_timer_get(...)
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- FuriHalCortexTimer beginTimer = furi_hal_cortex_timer_get(0);
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- This gets the current time in beginTimer.start.
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- The offset is 0 (we could use offset ).
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- furi_string_printf(str_buf, "Distance: %0.2f cm", (double)plugin_state->distance);
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- This rounds the output to the nearest hundredths place.
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- hc_sr04_duration_to_cm(...)
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- 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.
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- 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.
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