Ultrasonic beacon from HC-SR04s

Other Hardware Sensors
1

Hi,

I would like to build a beacon which then can be detected by my robot.
As I have some HC-SR04s available I thought I could use one as sender and a few on my robot as receivers.

Is it possible to use such a ultrasonic module as receiver only?

Is the approach realistic at all?

Thanks
Robert

2

Maybe tape something like foam over the transmitting element. then when you send init wait to hear from a beacon. IR beacon may be easier to home in on as you can make your sensors cover a narrower angle by burying them in a tube.

3

The processor on the HC-SR04 only checks the input after sending out the pulse. To use one as a receiver you have to pulse its trigger input at the same time the sender's trigger input is pulsed. You can do that via radio.

You might be able to take out the built-in processor (the middle chip, some kind of PIC processor) and get deeper control of the ultrasonics. Two pins go to the sender via the MAX232 chip. Set one pin HIGH and one pin LOW and alternate 80,000 times per second. The MAX232 will change the HIGH to -12V and LOW to +12V to put 24V across the ultrasonic sender. There is a third pin which uses a transistor to control power to the MAX232 chip. Maybe the 40 kHz signal is constant and the output is turned on and off with the transistor. An oscilloscope should tell.

Another pin comes from an op-amp (the third chip) connected to the receiver. That's the one you'd want to check for an echo.

Send out a pulse and have the beacon reply a fixed time later. The time of arrival of the echo will tell you how far the beacon is. Two receivers and some trig will get you the direction as well as distance.

4

Thanks a lot for the extensive explanation! I tried rapidly firing both SR04s. Works – but not too reliable.
Connecting them via radio might be required.

5

ultrasonics tend to bounce around the room quite a lot as well,

can be difficult to find which is source and which is echo. especially if near a hard wall.

6

Most beacons are done infrared. You could let each beacon send its own signal (right front corner, kitchen, etc.)
could be done cheap

7

That's what I am currently looking in.
Started with ripping of an old CD player for the IR sensor. Works great across the room with the original remote.
Currently trying to get it as directional as possible.

Then I'll try my own beacon.

Thanks
Robert