I have several HC-SR04 modules which I wish to modify. There are two modifications in particular I want to ask about

First, I am going to use two modules in parallel to determine location as opposed to distance. I’ve seen a project where two modules are connected in parallel and triggered together. The distances returned are then used to triangulate a position. In the article, one transmitter was disabled by attaching foam in front on one transmitter.

I was able to find the article to which I’m referring. http://forums.parallax.com/discussion/134899/triangulation-with-a-ping-array

I want to totally remove the transducer. I plan on testing whether the module without the transmitter can still detect the ping from the second module.

If not, what passive components could be used in place of the removed transducer? I’ve searched for an answer but have been unsuccessful in identifying a solution.

Secondly, I’d like to mount the second transmitter away from the module. I’d like to have the two receivers mounted about 3” apart and the transmitter to be centered between the two. This implies that the receiver will be extended by at most 1.5” from the module. Can I just wire the transducer with shirt extension wires? Should the extension be shielded? What wire gauge be used (are thinner or thicker wires better)?

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  • \$\begingroup\$ Look online, the circuit for these has been reverse engineered, there is almost certainly some surface mount component you can remove to disable the 2nd transmitter. Another strategy would be to use both by fire them at different points in time. Or just fire them at the same time. \$\endgroup\$ Jun 16 '19 at 12:32
  • \$\begingroup\$ 1) You need 3 receivers to triangulate. 2) You don't need a separate transducer to send and receive, but I guess you already have the pictured product. 3) It's not clear that you need to trigger the unit in order to receive, the timing seems to be done in software and visually it looks like there is just some op-amps and a logic converter. Try aiming one unit at another and read the Trig pin. 4) Why do you have a second transmitter? \$\endgroup\$
    – hekete
    Jun 16 '19 at 13:51
  • \$\begingroup\$ The unit is a transmitter-receiver pair. I want to disable the transmitter on two units so that I’ll have one transmitter and three receivers to triangulate. I’ll try removing a transmitter and breadboard two modules to see how they work. It occurred to me I could just use three modules and trigger each one separately. Another post did this with five modules and suggests using a 33ms between triggers. This seems reasonable if all else fails. I’m looking to locate a person at a distance of 1 meter. A 66ms delay appears to be reasonable in that scenario. \$\endgroup\$
    – djsfantasi
    Jun 16 '19 at 22:16

what passive components could be used in place of the removed transducer?

The dominant equivalent component is a capacitor. The value varies from transducer to transducer. A measurement of one example was 1.3 nanofarads.
Since the circuit is unknown, it is impossible to say if a transducer should be replaced with an electrical equivalent...no replacement part would likely cause no damage. Try it.

Can I just wire the transducer with short extension wires? Should the extension be shielded?

Yes, some inches extension should be OK. Shielded wires would be OK, but simply twisting those two insulated wires together should do just as well. Electrically, pulse timing is affected an extremely small amount by an extension, but acoustical pulses do change to a far, far greater degree. You can safely ignore the electrical effect of an extension provided it is not too far.

  • \$\begingroup\$ As some(most?) ultrasonic devices use the transducer as a part of the oscillator, the inductivity and resistance of the part is also crucial. But a ceramic cap should do. \$\endgroup\$
    – Janka
    Jun 16 '19 at 14:35
  • \$\begingroup\$ That one seems to have a separate oscillator? Any way I doubt the receiver stops working if you remove the transmitter. From looking at the back, they don't share the amp or anything. \$\endgroup\$
    – hekete
    Jun 16 '19 at 14:45

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