Go Down

Topic: sine wave generator (Read 9376 times) previous topic - next topic


Look at changing the PWM frequency to 40KHz. This is much better than using a loop. Otherwise you can get a NE555 to generate it for you.
Also 25uS is 25 micro seconds 10 -6 where as the delay function gets a number in milli seconds 10 -3.


Jun 25, 2011, 02:32 pm Last Edit: Jun 25, 2011, 02:37 pm by MarkT Reason: 1
Just to clarify a point touched on earlier:

Ultrasound travels through air.
Ultrasound travels through wood.
Ultrasound does NOT like to travel between air and wood (or any solid/liquid)...  There's a *massive* accoustic mismatch leading to extremely inefficient transfer of energy between the different media.  To a good approximation all the ultrasound is reflected by _any_ surface - which is why its very useful for proximity detection.

You need a transducer as used for ultrasound scanning (used with gel to acoustically contact the surface), not one for use in air.  These usually run at much higher frequencies (> 1MHz) for higher spatial resolution.

Also we've only discussed the transmitter side of things, no mention of the receiver which is the more tricky circuit.

[ for the record speed of sound in wood is about 3600 m/s (ten times faster than in air), so for a resolution of 1cm you need around 360kHz, for 1mm 3.6MHz... ]
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]


@markT: yes, that's why I i'm going to use direct contact (no air gap), i am going to use a coupling material.

@grumpyMike : I tried the PWM but I cannot change the frequency. I am new to arduino and the PWM (default peroid is short)


Go Up

Please enter a valid email to subscribe

Confirm your email address

We need to confirm your email address.
To complete the subscription, please click the link in the email we just sent you.

Thank you for subscribing!

via Egeo 16
Torino, 10131