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By anstimp
I need to emit a single frequency above human hearing and then convert that sound into audible sound to be heard through a pair of headphones.

This part is the part that is going to sound silly but bear with me.
I need to walk around blindfolded and still be able to comfortably get around without bumping into anything.
My idea is to bounce a ultrasound frequency off of walls and then back to a receiving device (microphone), convert to audible sound so I can hear the reverberation in my headphones. Why do I want to use ultrasonic? I don't want to bother anyone around me with a noisy "gadget" while I'm at the mall testing it. The unit should all be small enough to house in a pair of sunglasses.

I bought an Uncle Milton's Secret Sounds device (cheezy I know) and pulled it apart to expose the electronics. The emitter speaker is too large for me to use. I need something smaller. Any suggestions?

I'm not an electronics engineer. I'm an IT guy. I can solder.

Can you help?
By skimask
You might want to google the term "super superheterodyne"
The jist of the story... You mix two signals, you get 4 signals out -- The original signal, the signal you mixed in, the two signals added, the two signals subtracted.
So, for instance, say you're sending out a 40khz signal, and bouncing that around, and receiving that same 40khz signal.
You mix that signal with, say a constant 39khz tone. The outputs (in theory) will be 1khz, 39khz, 40khz, and 79khz.
You put the output thru a tight 1khz low pass (or band pass) filter and all you should hear is the one 1khz.
Now, this is all in theory, and really depends on well designed filters and such. A crappy designed filter will have all sorts of distortion and/or just plain may not work. But in the event it does work, it just might be good enough for what you looking to play with.
By Blackfin
Do you only need to worry about walls or could there be, say, knee-level obstacles like tables to worry about?

To be honest, I'd try to apply the KISS principle to this problem.

Use an ultrasonic range finder such as SEN-08502 mounted to a hat, facing forward. Use a simple microcontroller with PWM ability to control it. The micro determines if the return from the rangefinder is, say, 2 meters (7.9 ft), the PWM starts. The PWM is used to drive a simply headphone amplifier and ranges from, say, 500Hz to 3kHz. The frequency used is scaled to the rangefinder results so that at 7.9 ft (or whatever), the PWM starts humming at 500Hz. As you get closer, the PWM is increased until it hits 3kHz when you're, say, a foot from the wall.

You could get fancy: Use two sensors, pointing 45-degrees from each other. Use can use a couple of PWMs to give a "stereo" effect in the headphones (and perhaps volume control) to help "steer" the person: The side with the higher frequency indicates a wall close on that side...

I don't think trying to get fancy with heterodyning and mixing frequencies is needed here.
By anstimp
All of you are amazing! I never knew there was already so much out there.

On another note: Here's another stipulation as if it wasn't complicated enough already. The range finder is fine but I need something that could pick up echos so that I can tell the characteristics of the objects not just the distance from them. For instance, if I were to walk down the street would I be able to tell the difference between a trashcan and a fire hydrant just by sound without physically touching it. Here's my inspiration: Ben Underwood. Here is the youtube video.
By anstimp
Blackfin wrote:Do you only need to worry about walls or could there be, say, knee-level obstacles like tables to worry about?
I do need to worry about most all surroundings not just walls. You are correct in assuming.
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