Bought a ultrasound ranging module, link to the data sheet here:
http://www.micropik.com/PDF/HCSR04.pdf
Was just wondering if I could easily make this into just a ultrasound detector for 40kHz frequency
Have tested it and will only see if anything is being detected once the trigger pin is high.
How do I get it to always be detecting for the signal?
Here is a pic of the circuit:
http://www.micropik.com/PDF/HCSR04.pdf

 

Welcome to AAC!
Since the minimum detectable range is 2cm, it seems the unit is pre-programmed to wait a fraction of 1mS from the trigger initiation before enabling the receiver function. Without replacing the OEM controller IC with a custom version I don't see how you can get a continuous receiver function. The best you could do, IMO, would be to use a pulse generator to create a brief trigger signal at ~20mS intervals (corresponding to the maximum 4m range). Removal of the Tx transducer would be optional.

 

Thank you very much