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bagi
09-21-2005, 12:14 AM
how do i make a ckt for obstacle avoidance

rao
09-21-2005, 11:42 AM
The basic principle behind obstacle avoidance is reflection... you get your IR or ultrasonic soundwaves reflected from the obstacle to your reciever and hence detect and possibly avoid the obstacle..

Both sound and Light are as such too weak and divergent to travel a respectable distance and get reflected back carrying a detectable intensity.. to over come this problem.. you increase the power and modulate the sound or light.. the general frequency range lying between 30khz to 40khz...

You can use simple IR for starters.. you can modulate your IR beam to 38Khz.. that giives range and immunity from wide dispersion.. then Use TSOP1738 as a reciever.. keep the reciever right next to the IR LED facing the same direction as the LED.. so when IR radiation is reflected from the object in front.. the reflected wave hits your reciever and the delay between transmission and recieving can be the measure of distance...

Similarly, you can use piezo speakers and transducers for Ultrasonic obstacle avoidance... you can modulate sound in ultrasonic freq i.e around 40 Khz and throw it.. sound overcomes the dark body limitation of light and hence turns out to be a better means of range finding..

hope this helps..

Rao

09-21-2005, 06:52 PM
the reflected wave hits your reciever and the delay between transmission and recieving can be the measure of distance...

Its not easy to measure time taken by light to reflect back. Say ur uC is clocked at 16Mhz. so the least measureable unit of time is 1/16000000 s. in that time light can travel upto 18.75 meters. so the accuracy is plus or minus 18.75 meters !!

this could be done using some analog arrangement, never tried though.

rao
09-21-2005, 08:04 PM
compare the waveform's frequency and when you get an exact replica of the transmitted wave ( you gotta tune your circuit for that).. thats when you measure delay. and believe me.. that takes time.. or else rangefinding wouldnt have been there,,,

Rao

cheenu
09-21-2005, 10:50 PM
hi Rao,
U have proposed the use of piezo speakers and transducers for constructing the ultrasonic range finding module. Can u elaborate on it. Or could u point to some other reference which explains how this can be done.
Thanks in advance,

With Warm Regds,
Cheenu.

subot_robot
09-22-2005, 12:26 PM
For a beginner, the best way to implement obstacle avoidance is to use bump sensor (switch) to detect whether the robot has collided into obstacle or not. It's the simple method with checking whether switch is on or off.

subot.robot

sumandeep1984
09-23-2005, 04:29 PM
I imported a SRF-04 SONAR rangefinder by Devantech ... has given me very satisfactory performance.

Till now the discussion in this thread has been only on obstacle detection ... not on avoidance as asked by 'bagi' ...

rao
09-23-2005, 11:05 PM
How does an ultrasonic system work?? when the diaphragm of the reciever recieves the ultrasonic frequency, the piezo crystals are so configured so as to experience enough pressure at a fixed frequency to generate a detectable signal which is further amplified and used (synthesized or compared )... a peizo speaker or tweeter are capable of creating ultrasonic sounds.. as most other beepers (e.g your computer beeper) are not..

Hence the detector circuit is formed out of the speaker and transducer..

Correct me if I am wrong..

Rao

cheenu
09-24-2005, 05:17 AM
Hi Rao,
Ur explanation seems to be satisfactory. But u havent mentioned about any circuit to do that. Have u done this before? If yes can u post the circuit diagram? If no, where did u get the idea from? any site or book?. It would be useful if u mention the source.
Getting a ultrasonic module and making it to work would be easy. But the problem is inavailability. So we will have to work out some solutions so that we wil develop these devices ourselves. Thats the point. Afteralll this site is for indians to get into robotics.

Thanks,
with regds,
Cheenu.

venky
10-03-2005, 10:33 PM
well a very simple way would be to keep 2 piano wires as described in this link
http://beamindia.solarbotics.net/firesensors.htm
now if want to use IR sensors use the 555 timer & IR emitter module to generate pulses of around 38khz. the reflected rays r made to fall on an IR sensor linked o any amp amp for amplification of signals & the output fed to the microcontroller.
u can find a tutorial in
gorobotics.net

quasar
10-07-2005, 05:18 PM
Its not easy to measure time taken by light to reflect back. Say ur uC is clocked at 16Mhz. so the least measureable unit of time is 1/16000000 s. in that time light can travel upto 18.75 meters. so the accuracy is plus or minus 18.75 meters !!


Oopsssss... ultra sonic is a sound wave and not a Electromagnetic wave...... so it moves in the speed of sound.... and not the light.... Okkk


compare the waveform's frequency and when you get an exact replica of the transmitted wave ( you gotta tune your circuit for that).. thats when you measure delay. and believe me.. that takes time..

I am not getting....what u mean.......


else rangefinding wouldnt have been there,,,

Range finding in engineereing (let us say constrution and millitatry) genrally use... TOF method (time of flight).. but when they want accuracy they use the difference in phase change
and calculate it......

I think D misconception are now cleared...


Quasar..

rao
10-07-2005, 08:47 PM
Ok ..

someone finally replied to this thread..
:D

Speed of sound.. thats right...

Yeah.. by tuning the ckt I meant removing phase shift or calculating it(I know 567 does that, and I usually use 567..).. Other wise using a comparator with a test frequency also gives the proximity..

Thanks for answering!! :D

Rao

P.S. that ws a serious thanks and not sarcastic

addy
12-18-2005, 01:43 PM
i used a srf04 sonar module by devantech...
works gr8 for gud distances...

addy
01-05-2006, 01:07 PM
check out www.hobbykits4u.com
they seem to have gud modules....

taknev13
01-05-2006, 10:28 PM
hmm for a newbie as u said bump sensors wud be good enuf but thats gud if you dont mind colliding wid the object n den reversing.

ir sensors as said has the problem of colours but is gud in the sense as it does not require you to hit the obstacle to find out about it.the good thng here is it can be made to work for very small distances.

ultrasonic sensors as they say is meant for long range distance finding n can be used for obstaclke finding too.but cant find out small distances very accurately.it is more useful in cases of range finding n stuff.

n ya if u r a newbie n looking for some readymade stuff of ir n ultrasonic sensors in india then maybe u cud get in touch with a company called

ROBONENCE ph 080-41526083 Contach person MR suraj

they will definately help you with all this.

addy
01-06-2006, 03:01 AM
hi taknev....
ir's doesn fails completely for black surfaces....
they ll be detected but the range drastically decreases....
and they ll be surely detected if the surface is shinny....

taknev13
01-06-2006, 11:21 AM
ya addy thats wot i meant it works the exact way u said.

cannot express evrythng n words :D

addy
01-06-2006, 03:18 PM
hi taknev.....
yeah u r correct....
i said man tat it doesn gives the desired response as u ll expect... tats it!!
but still if u r measuring the time gap between the 'ping' and time u recive it back.... then u can 'exactly' predictly distance and then it ll work fine giving u corect distance between the obstacle and the robo..