Sonar JSN-SR04T

OK I have hit the jackpot! I finally found the SR04 to i2c code that I knew existed out in the wild. this gives us 2 things, the ability to scale the rangefinder to work in water and the ability to run multiple rangefinders without using lots of gpio, I have edited this version to multiply the range so it shows up correctly when in water. its not as fast or accurate as serial mode but because the scaling is done before it gets to the flight controller it means it can be used for proximity and not just alarms.

// sr04 to apm I2c sonar
// by panxu mail:
// Created 2014
#include <Wire.h>
#include "SR04.h"
#define TRIG_PIN 2
#define ECHO_PIN 3
SR04 sr04 = SR04(ECHO_PIN,TRIG_PIN);
uint16_t reading_cm;
uint16_t tempread;
void setup()
  Wire.begin(0x70);                // join i2c bus with address #2
  Wire.onRequest(requestEvent); // register event

void loop()
  if (tempread<1500)  
void requestEvent()
  byte sendhi;
  byte sendli;
  byte sendbyte[2];
  uint16_t tempreading_cm;


Tested with my test rig.

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Excellent result, especially since the scaling parameter is not added in the new version(4.2). I also like that it’s on i2c, not on gpio.

yes having it on i2c opens up a lot of options, im adding another 3 under my boat looking forward left and right so I have underwater proximity alerts. you just need to change the i2c address in the arduino sketch to get around address conflicts, I have tested it running 2 so far without issue.

Now you can test and see how stable the sensor behaves.

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In order to read the sensor at maximum speed you would need read the serial stream directly from the sonar its self. currently there is no native serial driver but this is a serial lua driver that @Yuri_Rage created. its very fast but because the rangefinder is being read into lua but there is currently no lua binding for a rangefinder so it can only work within lua for actions and sending alerts and values it wont work with avoidance or anything like that currently.

local SCRIPT_NAME          = 'Depthfinder'
local MAV_DEPTH_LABEL      = 'DEPTH'
local BOOT_DELAY_MS        = 2000
local RUN_INTERVAL_MS      =  50
local SERIAL_PORT          =    0
local BAUD_RATE            = 9600
local FRAME_SIZE           =    4
local SPEED_RATIO          =    4.126
local INVALID_DEPTH        =   -1
local MAV_SEVERITY_INFO    =    6

local port = serial:find_serial(SERIAL_PORT)


local function serial_flush(bytes)
    for i = 0, bytes - 1 do

function update()
    local bytes_available = port:available():toint()

    if bytes_available ~= FRAME_SIZE then
        gcs:send_named_float(MAV_DEPTH_LABEL, INVALID_DEPTH)
        return update, RUN_INTERVAL_MS

    local data = 0
    for i = 0, bytes_available - 1 do
        data = data << 8 | port:read()

    local sum    = data & 0xFF
    local l_data = data >>  8 & 0xFF
    local h_data = data >> 16 & 0xFF

    if (0xFF + h_data + l_data) & 0xFF ~= sum then
                      string.format('%s: Bad checksum', SCRIPT_NAME))
        gcs:send_named_float(MAV_DEPTH_LABEL, INVALID_DEPTH)
        return update, RUN_INTERVAL_MS

    local depth_raw = h_data << 8 | l_data
    --gcs:send_named_float('RAW', depth_raw)
    gcs:send_named_float(MAV_DEPTH_LABEL, depth_raw * SPEED_RATIO * 0.001)

    return update, RUN_INTERVAL_MS

gcs:send_text(MAV_SEVERITY_INFO, string.format('%s: Script Active', SCRIPT_NAME))

return update, BOOT_DELAY_MS

I have tweaked the code by swapping the trig and echo pins and redesigned the sonar board mounting to make it as slim as possible.

I have been busy, I wasnt happy with the arduino converter as it was still getting read as a Sr04 rangefinder without all the benefits of serial mode. so this is my latest creation, Using the TFmini>maxbotix i2c adapter @ppoirier made as a start I copied in the serial sonar code from an example script i found and now its working!

I have made another version of the serial i2c adapter that should work with the rangefinder in mode 1 and mode 2, so its only pinging if requested rather than every 100ms. it should give more stable returns as it will be going through all the rangefinders sequentially rather than them all pinging constantly.

latest version is fully operational with averaging and mode selection

found some technical information on the jsn-sr04t