HC-SR04 Hack

Other Hardware Sensors
1

Hey all, I would like to measure a distance with HC-SR04 the way sensor works is the echo length corresponds to distance so it give something like this on the scope :

| |

what my prof wants to see is a trigger signal and a received signal then the distance between them, like below :
__
Trigger: | |______
__
Received: ______| |

But this isnt how HC-SR04 is designed, the sensor unfortunately doesnt have any schematics or a proper datasheet. I was able to find the trigger signal, but I cant find the received signal, there are around 24 pins behind I tried all of them one by one with the scope but couldnt succeed. I would be glad if you can give a hint...

Summary : where shall I put the scope probe to catch the received pulse... to display on scope?

2

http://elecfreaks.com/store/download/HC-SR04.pdf

3

Yes like I said, it doesnt have a proper datasheet, I added elecfreaks to my skype but they didnt give me any schematics or further help.

4

Did you try looking at the output of the pin labeled "ECHO"?
It seemed very clear from the data sheet that this is exactly what you wanted.

5

The pin ECHO gives the first output which I drew, this is how HC-SR04 works usually but I would like to find the pin which gives the "recieved" pulse and has a small peak like I drew on the second drawing(Trigger & Received)

6

The module can't send back the echo pulse until it has actually received an echo. Furthermore, there probably isn't much of a delay (certainly less than 1 millisecond and most likely a constant) between the onset of the return pulse and the beginning of the echo pulse.

I will bet that with some trials, you could figure out the delay fairly precisely. Set the module to be several different known distances from a wall and investigate the timing.

7

jremington:
you're clearly not understanding the question. the echo pin returns a pulse proportional in length to the delay between the TX and the RX. student7's question is how to get the raw sonic data coming back, which would be (approx) a fixed width pulse but with a delay (before the pulse starts) corresponding to the distance.

student7:
did you find the answer? (i have the same question...)

8

student7's question is how to get the raw sonic data coming back,

That's not how I read it.
The solution I see simply turns the falling edge of "echo" into a rising edge.
If you want the raw return, just scope-up the rear of the Rx transducer; it isn't rocket surgery.

There used to be full schematics available for the very similar Devantech devices.

9

you could connect it to the Arduino pin 2 , use attachinterrupt and when the signal changes generate an appropriate signal on 2 output pins.