Some days ago I got tired of messing around with my circuits and finally ordered some HC-SR04 boards. There is everything I need packed together on one board: Transmitter and receiver and some controller.

Here I found a really good analysis of the HC-SR04. It seems like its receiver circuit is quite simillar to mine, allthough it works ways better.

With this plan on hand, it took me only a few minutes to capture the next two images.

What can be seen is the input of the receiver after the third input stage (analogue, I want to capture this) and the related output of the controller (TTL, won't be useful for me).

With different distances to an object moves the time between sended and received pulse, on the first measurement the distance was ~35cm, the second time it was shorter.

Update:

Here is a photo of one transmitter/receiver (top) and three receivers:

Note that I removed the transmitter and added a pull-down on Trigger-In line.
For connecting the boards I used USB cable, it's got a shield and hopefully running power and signal lines together is no big deal for this application. If signals are bad, I'll swap the cable or add a second, shielded cable for the analogue signal.

This is how the boards look like from the back

And this is the box, where all sensors will plug in.

Details on the box will follow with my next project log.