I'm trying to make a project which demonstrates Doppler effect. In short, the transducer emits a ultrasonic wave, wave reflects from rotating disk and then goes back to microphone. I need to show that the frequency of the reflected wave will be different from the emitted. So, I need an ultrasound transducer and ultrasonic microphone.
I did some research before and found HC-SR04 sensor. Is it suitable for my project? Can I turn it into frequency counter mode or do I need something different for my purpose? I need at least 40 KHz. I can buy MA40S4S and MA40S4R but I've found no solid info about arduino compatibility. Any ideas?
Thank you.
Sorry for possible mistakes and inaccuracies, I'm still learning English
Can I just use oscilloscope as frequency counter or I need separate device?
Possibly... Some modern digital oscilloscopes have a frequency counter built-in. Or, you can directly see the waveform change if you can sync the 'scope. The 'scope and frequency counter like see a nice "smooth" continuous signal/waveform (and your eyes like to see that too). If the frequency is rapidly changing/jittering it might be hard to display or measure the effect.
...The classic train whistle doppler effect would be easy to measure or display on a 'scope because it lasts for several seconds.
...The Arduino ADC only samples accurately up to around 15kHz sample rate (limiting you to signals of around 7kHz) so the analog input is out of the question and the digital input is also unlikely to work because you won't get "clean" reflected acoustic pulses.
Ok, I need to check my university's oscilliscopes.
But my disk will fastly rotate, so it means the microphone input will be quite messy? Is it possible to make relatively cheap frequency counter which can work with ultrasound frequencies?
If you calculate the speed of that flat side surface is moving in m/sec, than frequency deviation could be derived.
I'd expect less than 1%, probably 0.1, though very likely you would not be able to measure with a scope or hardware based frequency counter.
HC-SR04 may works, if analog output is taken out from comparator input, there are on-line resources to do this hack.
I'd use rotational encoder to have strict synchronization between wheel position, timing to pulse ultrasonic wave by HC-SR04 and timing to capture reflection.
Arduino DUE would be suitable platform to sample input at 1 MHz.
When you get to this stage, than you could open a door to another dimension, DSP processing, that could trace micrometers /sec movement astonishingly accurate.
