View Full Version : Range on IR Object Detectors

01-28-2010, 11:51 AM
Hello all!
I'm working on building a small, autonomous robot capable of detecting objects. It moves quite quickly, so I'd like it to be able to "see" objects about a meter away, so it can do a graceful turn rather than smashing into it, backing up and trying again : ). However, using the IR LED and Detector setup, I haven't been able to get a range of more than about twenty cm. I've heard of ranges over five feet, how can I achieve that?


01-28-2010, 12:07 PM
Sharp IR sensors will range to 80cm and the Ping))) will do more I think.

- Stephen

01-28-2010, 09:31 PM
Yeah, but how do I connect them or code them differently to achieve greater range?

01-28-2010, 09:59 PM
The 'ping' sensor is good from a few centimeters to 10 feet. 5 feet is quite a distance for IR-reflection -- sound reflection as used by the 'ping' would probably be better, backed up by close detection of IR-reflection.

01-29-2010, 01:45 AM
Eleven different IR sensors at http://www.junun.org/MarkIII/Store.jsp (and·five different sonar sensors). I'd love to see a side-by-side comparison of range & features vs price.

·"If you build it, they will come."

01-29-2010, 04:12 AM
In the Basic Stamp application notes, they show how to make a serial data transmission through IR with a range of 10 ft. So, IR reflection should be good to slightly less than 5. I've made the circuit and code exactly like in the notes. Has anyone had any success at moderate ranges for IR object detection. I'd rather not use the PING just on a basis of cost and simplicity.

01-29-2010, 08:16 AM
Neither traditional IR nor sonar is totally foolproof. An object's size, shape, location, texture, and angular orientation (normal, perpendicular, 45 degrees) will drastically affect the reflection of the IR or ultrasonic signal. You may want to use both on a fast-moving robot to cross-check each other for reliability.

·"If you build it, they will come."

01-29-2010, 08:20 AM
True enough, however the 20cm range I have is drastically and unexpectedly different from the approximate 120cm (4 ft) range I should be able to attain. I'm just wondering why and how to fix it.

01-29-2010, 11:17 AM
You could start by showing us your circuit your part numbers and attaching your code to a post.

- Stephen

01-30-2010, 01:13 PM
Right. Sorry, that would have been a good way to start. I'll have them up soon. It's exactly like what's described in the SumoBot manual; code, circuit and all. You can download the manual from the Parallax product page. Either way, I'll post it soon.

01-30-2010, 02:21 PM
erco said...
Neither traditional IR nor sonar is totally foolproof. An object's size, shape, location, texture, and angular orientation (normal, perpendicular, 45 degrees) will drastically affect the reflection of the IR or ultrasonic signal. You may want to use both on a fast-moving robot to cross-check each other for reliability.

Don't forget color for IR!

01-30-2010, 10:58 PM
While I'm putting together my diagram, has anyone tried this sort of detection themselves? If so, what sort of range did you get?

02-05-2010, 08:15 PM
Okay, reverting to good 'ol ascii:

P1------(220 O Resistor)---------(IR LED)----------VSS


And here's the code snippet:

' {$STAMP BS2} ' Target = BASIC Stamp 2
' {$PBASIC 2.5} ' Language = PBASIC 2.5

' -----[ I/O Definitions ]---------------------------------------------------

LMotor PIN 13 'Left Motor
RMotor PIN 12 'Right Motor - all wheel commands must be backward for this one only

lpwr PIN 10 'Power out to the left QTI
lin PIN 9 'Left QTI in
rpwr PIN 7 'Power out to the right QTI
rin PIN 8 'Right QTI in... Does anyone know what QTI stands for?

IrLedLS PIN 1 'Left IR LED
IrSenseLS PIN 6 'Left IR detector

IrLedRS PIN 2 'Right IR LED
IrSenseRS PIN 5 'Right IR detector

IrLedB PIN 0 'Rear IR LED
IrSenseB PIN 3 'Rear IR detector

irledfl PIN 4 'Front Left IR LED
irsensefl PIN 11 'Front Left IR detector

irledfr PIN 15 'Front Right IR LED
irsensefr PIN 14 'Front Right IR detector

' -----[ Constants ]----------------------------------------------------------

IrFreq CON 38500 ' IR LED transmit frequency

' -----[ Variables ]----------------------------------------------------------

IRBits VAR Byte 'State of IRs
irfl VAR IRBits.BIT0 'front left
irfr VAR IRBits.BIT1 'front right
irls VAR IRBits.BIT3 'left side
irrs VAR IRBits.BIT4 'right side
irb VAR IRBits.BIT5 'rear
irb2 VAR IRBits.BIT6 'rearv2
irb3 VAR IRBits.BIT7 'rearv3!

IRBackupBits VAR Byte
irfl2 VAR IRBackupBits.BIT0
irfr2 VAR IRBackupBits.BIT1
irls2 VAR IRBackupBits.BIT2
irrs2 VAR IRBackupBits.BIT3
irb4 VAR IRBackupBits.BIT4

lintense VAR Word
rintense VAR Word
lintenseb VAR Bit
rintenseb VAR Bit
temp VAR Word
cycle VAR Word

' -----[ Initialization ]-----------------------------------------------------

DEBUG CLS, "IR DETECTORS", CR, ' Display heading
" FL FR Left Right Back LLight RLight", CR,
"----- ---- ---- ----- ---- ------ ------", CR

' -----[ Main Routine ]-------------------------------------------------------
FOR temp=1 TO 103

GOSUB checkleft
GOSUB checkright
GOSUB checkfleft
GOSUB checkfright
GOSUB checkrear

HIGH LPwr ' activate sensors
HIGH LIn ' discharge caps
RCTIME LIn, 1, lintense ' read left sensor
RCTIME RIn, 1, rintense ' read right sensor
LOW LPwr ' deactivate sensors

LOOKDOWN lintense, >=[1000, 0], lintenseb ' 0 = black, 1 = line
LOOKDOWN rintense, >=[1000, 0], lintenseb

DEBUG CRSRX, 2, BIN irfl, ' Display object detect bits
CRSRX, 9, BIN irfr,
CRSRX, 17, BIN irls,
CRSRX, 23, BIN irrs,
CRSRX, 32, BIN irb,
CRSRX, 41, DEC lintenseb,
CRSRX, 50, DEC rintenseb
' IF temp<50 THEN
' HIGH rled
IF temp>101 THEN
' LOW rled

checkfleft: 'Check the front left IR
FREQOUT IrLedFL, 1, IrFreq
irfl = ~irsensefl
IF irfl=1 THEN
FREQOUT IrLedFL, 1, IrFreq
irfl2 = ~irsensefl
IF irfl2=0 THEN : irfl=0 : ENDIF

checkfright: 'Check the front right IR
FREQOUT irledfr, 1, irfreq
irfr = ~irsensefr
IF irfr=1 THEN
FREQOUT IrLedFr, 1, IrFreq
irfr2 = ~irsensefr
IF irfr2=0 THEN : irfr=0 : ENDIF

checkright: 'Check the right IR
FREQOUT IrLedRS, 1, IrFreq
irRS = ~IrSenseRS
IF irrs=1 THEN
FREQOUT IrLedRS, 1, IrFreq
irrs2 = ~irsenseRS
IF irrs2=0 THEN : irrs=0 : ENDIF

checkleft: 'Check the left IR
FREQOUT IrLedLS, 1, IrFreq
irLS = ~IrSenseLS
IF irls=1 THEN
FREQOUT IrLedLS, 1, IrFreq
irls2 = ~irsenseLS
IF irls2=0 THEN : irls=0 : ENDIF

checkrear: 'Check the rear IR
FREQOUT IrLedB, 1, IrFreq
irB = ~IrSenseB
IF irb=1 THEN
FREQOUT IrLedB, 1, IrFreq
irB2 = ~irsenseB
IF irB2=1 THEN
irB3 = ~irsenseB
IF irb3 = 1 THEN
FREQOUT irledb, 1, IrFreq
irb4 = ~irsenseB
IF irb4=0 THEN : irb=0 : ENDIF

I know I don't depict which connection goes to which on the detector, but rest assured that it is connected properly.

Rick Brooks
02-07-2010, 07:57 PM

With your setup, you should be able to get about 40cm of range.· Remember that your sensors are looking at reflected IR light and a lot of power is lost in the reflection process.· If you had an ideal target (100% reflected IR) you may be able to get substantially more range.

I am assuming that you are using PNA4602 sensors and QEC113 IR LEDs.

Step 1 optimize the frequency.· It is my experience that each IR LED and sensors works best at one frequency.· Do frequency runs for each IR/sensor pair and choose the frequency that gives the maximum reliable range.· This is a time consuming process.· You will notice that the results do not come close to the expected Bell curve that you may be expecting.

Step 2 switch to the BS2SX.· It is a faster chip and does a much better job of reproducing the 38kHz signal which gives slightly improved results.

Step 3 increase the power of IR beam generated.· Using a 220 ohm resistor with the IR LED limits the current to 15 ma.· To get more distance, increase current.· Remember that the BS2 pins cannot generate much more current, so use a transistor to increase drive current.· I like to use MOSFETs for this.· In early experiments, I have driven a QEC113 with about an amp of current and have seen two to three meters detected range.· Just keep the total power low (one reading every 15 or 20 msec works) and the QEC113 will survive.· My test setup with 1 amp drive worked for over a week continuously before I got tired of running it.

One more note, beware of outside IR influence (sun light).· The PNA4602 has built in AGC circuitry that limits sensitivity based on total IR power detected.· When there is a lot of IR, the gain is reduced, so the detected distance is drastically reduced.· Basically, don't run them outside and stay away from windows on bright, sunny days.

·· Rick Brooks

02-08-2010, 10:43 AM
Thanks, Rick.

I was hoping I wasn't at max range already. Those are indeed the parts I am using, I think they're the only ones for sale by Parallax. As much as testing each pair's ideal frequency will be time consuming, I'm hopeful it'll work. Just so it doesn't take days, do you have any recommendation as to low and high ends and steps to go up by?

Thanks for the tip about outside light, I'll make sure to limit that. I was careful not to aim at windows or other sources because I assumed it would pick it up as a false signal. I didn't realize there was a gain built in for ambient conditions.

As for inserting a transistor, do you have any recommendations as to part numbers? Also, do I keep a resistor in, or can I chuck it?

Thank you very much for your helpful response.

Rick Brooks
02-09-2010, 05:28 AM

Let the stamp do most of the work for the freq run.

I normally start out with a range of 36kHz to 42kHz and 100 Hz·steps at about 10 inches distance.· At each frequency, run the freqout ten times (pause about 10 msec between readings) and debug the frequency and number of hits.· You will be looking for tens.· If you get all tens, move the object farther away.· Start limiting the frequency range and reducing length of the steps while moving the object.· After about five or six runs you should be down to 1 Hz steps.··A single (or a few) frequencies normally stand out from the rest.

Presently I'm using IRFD024 FETs for the IR LED drivers.· They are small and mounted directly beside the IR LEDs.· The FET gate can be driven directly from the Stamp pin.· Use a small resistor to limit currect to the IR LED to whatever level you need.· I use a 15 to 30 ohm resistor dirven by an adjustable voltage regulator.· The sensing range is controlled by the voltage from the regulator.

·· Rick Brooks

Post Edited (Rick Brooks) : 2/9/2010 12:53:33 AM GMT