sza2 / node_hcsr04 Goto Github PK

I used your code but I only get incorrect readings from the HC-SR04 sensor.

I did some debug modifications in the function self.measure() see below:

function self.measure()
gpio.trig(self.echo, "up", self.echo_cb)
gpio.write(self.trig, gpio.HIGH)
tmr.delay(100)
gpio.write(self.trig, gpio.LOW)
tmr.delay(100000)
if (self.time_end - self.time_start) < 0 then
return -1
end
-- Modified for debug purpose
print ("-------------------")
print (self.time_start)
print (self.time_end)
print (self.time_end - self.time_start)
print ("-------------------")
return (self.time_end - self.time_start) / 58

This is the debug printout of the self.time_start and _end

1079788923
1079789402

479

1079897355
1079897818

463

1080035710
1080036173

463

1080174067
1080174530

463

7

1080788919
1080789402

483

1080897355
1080897822

467

1081035711
1081036177

466

1081174065
1081174532

467

8

Do you have an explination to why the time between trigger and echo is constant at around 460-470 us even if there is nothing infront of the sensor.

Could you also explain why you devide the delta time by 5800, I am guessing it has something to do with the speed of sound in air. 343 m/s = 34300 cm/s

What am i doing wrong? ;)
Thanx for your support

Hi,

With my srf05 sensor I get readings jumping by ~1 meter - every 10seconds I get a drastically different reading.
Do you have any similar experiences? Or perhaps is it a faulty module?

after ~10 successful readings I will get an error -

PANIC: unprotected error in call to Lua API (hcsr04.lua:42: attempt to index global 'tmr' (a nil value))

line 42 is a delay(100) command... so is there something with the triggers making it screw up?

update: without sensor connected returns 0 and no errors. so probably some hardware issue.

I am able to make the module/setup work perfectly with the Arduino code and can confirm hardware is in proper order.

With this library unfortunately i get only -1 as a reading and sometimes 15 sporadically not sure what is the cause.

function self.measure() missing 'end' at end of if statement
function self.measure_avg() missing end at end of if statement