HC-SR04 trigger and echo

I’m new to arduino (infact opened box and started playing about 10minutes ago) and have an HC-SR04 setup and measuring the distance across my desk right now. However I want to play a little more and experiment. Is there anything in the electronics on the HC-SR04 that dictates, that the ping has to come from the same module as the echo is recieved. Or could I buy a second HC-SR04 and use that to send the ping, and then recieve on the original HC-SR04.

I.e. wire both up then use the trig on one unit, and the echo on the other?? Would it work?

You can do that, but you'd have to remove the transmitter transducer from the end that you wanted to be receive-only, to ensure you don't confuse returns.

Some of the Devantech devices (of which I suspect the HC-SR04 is a clone) allow you receive only.

Excuse my ignorance, but if the trig pin on the recieve unit is not connected, would you still need to remove the transducer??

i.e. use the trig pin on one unit, and the echo pin on another unit.

You may be in trouble.. How do you know when to start timing?

knut_ny: You may be in trouble.. How do you know when to start timing?

Same as when you have them both in the same module. When you send the ping from the first module, you wait for it on a different pin?? Am I missing something??

but if the trig pin on the recieve unit is not connected,

How are you going to trigger it to make it listen?

AWOL:

but if the trig pin on the recieve unit is not connected,

How are you going to trigger it to make it listen?

Thats what I was asking. So you need to wake the ultrasonic sensor up to listen, it isn't the arduino that knows to listen on a set pin??

The trigger pulse on the trigger pin causes the controller on the unit to first transmit the eight cycle transmit pulses, then raise the echo pin. The amplified received echo then causes the controller to lower the echo pin.

Okay so in effect when you send the trig to the sensor, it in fact also wakes it up to listen, as well as triggering the pin. I'm with you. So yes, I will have to gently unsolder the tranmitter, on the recieve only end. Once this is done, can I then wire the trigger pins together??

Ff both units are connected to the same arduino, you case surely trig them both with the same pin. Then wait for an echo on unit of your choice.

The plan was to measure the distance between to ditinct points, which with the range sensor as it stands isn't brilliant because neither is a flat surface. However if I mount the sensor at one end, and the reciever at the other, my theory is that it should work. I suspect I will have to remove one of the transmitters, so that they don't get confused. Then wire the trigs together, as originally suggested by AWOL.

..or dont trig it. ? Trig unit A.. listen for echo on unit B. Seems logical to me. No hardware mods to be done.

That was my plan, but there seems to be some suggestion that you'll need to wake up the second unit to get it to listen. Think the best thing is order a second unit, and when it arrives, try it, and see if it listens with me waking it up.

It looks like you will need to wake the second unit as suggested by AWOL.

I have recieved my extra SR04 (cheap copied incase I end up taking them apart) I have test 2 that work as individual units.

Then I have wired the +5 and gnd on both units but the trigg on one unit, and the echo on another unit. As predicted it is not hearing the echo. Switch the echo back to the same unit as the trigger, and it works fine.