Distance sensor from 38kHz receiver

weirdo · May 24, 2009, 3:17pm

It is possible to build ir distance sensor from 38kHz sensor. You need the sensor and IR led. Sensor's output goes to input pin and IR led's one leg goes to output leg so your controller is able to flicker it.

If the LED pulses at 38kHz (and 1kHz too if just pure 38kHz doesn't work) then the sensor is able to detect LED about 10 meters avay. If you mount them side by side then sensor sees things what are closer than some X range (lets say, 2m) and if there is no things closer then sensor sees nothing. Sounds pretty useless.. But now, lets look at the following graph:

Bingo. So if robot sees something when using 38kHz modulation then robot can increase modulation frequency until it sees nothing. Then it is possible to calculate(look up from table) distance by modulation frequency.

This sounds like something very complicated. But it doesn't have to be. It is possible to use just one modulation frequency. Then it is possible to say if there is an object closer than 20 cm or some other random distance.

And, the width of beam equals led's beam width. More than one sensor can be used but then they should be in shrinktubes or something so random ir light from other sensors couldn't shine at/in them.

rik · May 24, 2009, 4:15pm

This sounds like a proposal
Not so much a proven technique. Are you building one of these right now?

weirdo · May 24, 2009, 4:19pm

I havn’t built one, but
I havn’t built one, but local university built whole farm of robots (around 20) with 8 of these sensors on each robot. And it has been mentioned in couple of robot building books, so i am pretty sure it works. I wrote this tip thingy so more people could understand such possibility…

noise0 · May 24, 2009, 4:43pm

i am using one of those on

i am using one of those on my critter in the terrarium in order to detect charger beacon

it seems to work fine

MaltiK · May 24, 2009, 8:13pm

** I thought I saw these**

I thought I saw these somewhere:

http://www.solarbotics.com/products/k_sv/

“Two 38kHz IR emitters and detectors for opponent detection”

christhecarpenter · May 24, 2009, 9:56pm

Were we just talking about this?

Did you just re-write Salvage’s comment in the “I’m sick of Sharps” post?

Yeah, we got it… we all have the concept down now. Where is the prototype? Show me the money.

noise0 · May 25, 2009, 4:55pm

i have performed some test

i have performed some test varying modulation frequancy…

the test setup is this:

emitter and receiver are parallel facing forward (black tubed)

forward is a wall at a certain distance reflecting the beam back to the receiver

i can vary the frequancy of the emitter using a pot

the outcome is: yes, it’s possible to evaluate distance using the relation between sensitivity and frequancy

in my setup i am able to get readings down to 8 cm

christhecarpenter · May 25, 2009, 5:04pm

out of curiosity…

What was your max range?

Also, what type of IR LED were you using: Just one? Run directly off of the pic/556? Transistor switched or not?

noise0 · May 25, 2009, 5:51pm

half a meter was my max test

half a meter was my max test range because the wire was too short

anyway this device seems very fitting at long range…

i use standerd 940nm irled

direct driven from 555 (no transistor)

mintvelt · May 25, 2009, 6:09pm

nice
that sounds promising. I don’t understand 'bout the wire. you have a wire between the wall and the sensor?

noise0 · May 26, 2009, 3:34am

argh excuxe me, yesterday

argh excuxe me, yesterday nigh i was too stoned forgot about the wire

noise0 · May 27, 2009, 8:36am

this is my idea in order to

this is my idea in order to use this device as analog distance sensor

the trick is to FM modulate 38kHz carrier with a 1kHz sawtooth signal

the result culd be a pwm signal proportional to distance (lo-pass it and u got analogic reading)

lutenit030 · August 19, 2010, 7:15pm

Where is the table at the top of the page

The picture contained the table of freq Vs Distance at the top of the page seems to be no longer available

can any one help me finding it??

i have another question

if the IR sensor (i’m using 1838) does not detect any ir signal unless it was 38Khz it is supposed 2 have a buildin band pass filter

how would it detect any other freq??

Thanks in advance

weirdo · August 20, 2010, 3:09am

sorry
sorry for the 404, i am moving my site. pic is back and answers your question.

lutenit030 · August 20, 2010, 12:32pm

I’m willing to build this project But>>>

I’m trying to build this project but there is some isues i wanna ask about

The picture contained the table of freq Vs Distance at the top of the page seems to be no longer available

can anyone tell me from where i could get it ?

I have another question

if the IR sensor (i’m using 1838) does not detect any ir signal unless it is 38Khz

how would it detect any other freq??

Thanks in advance

lutenit030 · August 20, 2010, 1:14pm

**Thanks you **

Thanks u so much for your concern and sorry for reapeating my post cuz i’m new in this site and i thought that comments should be at the bottom of the page not the top sorry

i still little confused about some isues like what does “relative transmission distance100%” means

related with what??

any way i’ll try to build this project using atmega32 and i’ll inform u with my results