hi all

can anyone please help me make an ultra sonic proximity sensor. ive looked almost everywhere on the net for some schematics or circuit diagrams or instructions or explanations but it seems to be a lost cause.

i am building an obstical avoiding robot and i want to build a completely anolog ultrasonic sensor. i believe the main problem is the reciever. the range only needs to be a maximum of 20cm or 8 inches. please keep in mind i want to make this as cheap and simple as possible.

any help would be apreciated. thanx.
grim.

 

Why completely analog?

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Hmmm i think you have the concept wrong, it wouldnt be analog it would be digital...
If you have a uC this should be no problem at all!
You just need a ultrasonic speaker and microphone
Heres the flow chart:
Use the pwm module on the uC to generate a short blast of sound in the US range,
create a delay to ensure that the uC doesn't detect the actual initial sound,
Count time after that until pulse returns...then
(343m/s (speed of sound) * time it took)/ 2 (there and back) = distance from object
im pretty sure many go up until 2-4m, however im not sure what the closest resolution possible is but 20cm might be a bit close, perhaps whatever the closest range is, look at the speed of you robot then shut down after x seconds....?
There's tons of links:

A Cheap Ultrasonic Range Finder
Ultrasonic Range Meter


Mike

 

bridman, completly analog ultrasonic sensors can be made, digital ones are much more convient and easy to build though.

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They produce a voltage based upon the intensity of the reflected sound?
You would need to isolate the sensor from the emitter then no?

Mike

 

No birdman, you just turn the receiver on AFTER the direct wave has passed and all that can be received is the echo. A simple delay is all that's needed, it just needs to be fine tuned to allow sensing as close as you need it to.

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yeah i get what your'e saying. i do have a pic, however i want to make it completely analog with a digital output i supose. i want it analog because it leaves room for a more simple and reliable program. at the moment my bot has 3 IR sensors (front, left and right) so in my program my bot simply goes forward and tests to see wich sensors are triggered. the sensor being either a "1" or a "0".

although if i make it digital i supose i could just make it stop every few seconds and run a "sonar routine" so to speak. im just typing what im thinking at this point. but it would be a great learning experience if i made it completely analog.

by the way thanx for the link birdman, i understand the digital concept, and its benifits alot better now.

 

I don't much like Paralllax because of their prices but for the convience this one is well worth it.

PING))) Ultrasonic Sensor

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haha parallax wouldnt be an option for me. i live in south africa and judging how this project is going, i dont have the time or the money to wait for that to be shipped to me. basically i already have a tx and rx ultrasonic 40KHz speaker, and various components.

if i have a 40KHz pair as mentioned above, does that mean that the recieving speaker is only able of reading sound waves of only 40KHz or does it mean it is capable of reading sound waves "up to" 40khz? is that what the additional circuitry is for?....to cut off other frequencies and fish out the 40KHz only?....or to amplify the 40KHz it just recieved and output a "1" or a "0" accordingly?

thanx for your previous speedy replies by the way.

 

They're designed for peak resonance at 40khz, they have a greater range than that but the actual power out/in you'll get will not be linear over the full range. Generally you feed them a perfect sine wave at their resonant frequency (square will work) and listen to the receiver after delay through as narrow a 40kh bandpass filter as you can manage.

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ok so basically its just a speaker and a microphone, and the microphone has an external circuit (using opamps) that detects 40khz soundwaves and triggers wen it detects that soundwave?....in a nutshell atleast

 

Yep, pretty much. There's generally a delay between the transmitter pulse and turning the receiver on so the receiver doesn't detect the transmitter pulse, this (depending on the exact circuit) results in a slight deadzone just in front of the unit where it can't determine distance up close.

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ok thanx for the info.
well now i have decided to do the extra ordinary. ive decided to design and build my own US proximity sensor from scratch. im sure i could get this done in a day. im pretty irritated of scouring the internet for some sort of schematic to help me out. the problems i have found with the ones i have come across are that alot of the components are not as readily available here in South Africa. making the components a little more expensive than necessary and it is a huge mission trying to find equivalants.

if i get this working, i will post up a schematic (unlike the rest of the selfish electro peeps on the net, haha) and then maby members here can help make it more effecient.
i guess getting it working is the first step though.... ile keep you posted

 

hey guys i got it working. it only does short distances. about 20cm max. im a little busy with studies at the moment but when i get a chance i will post the schematic up for reference.

 

You should get better range increasing the voltage you're using on the Xmitter unit. Just be careful you don't exceed it's max power, if you do it'll just stop working.

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