Range on IR Object Detectors
Bootsy
Posts: 22
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?
Thanks!
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?
Thanks!
Comments
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
- Stephen
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
·"If you build it, they will come."
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
·"If you build it, they will come."
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
- Stephen
Don't forget color for IR!
P1
(220 O Resistor)
(IR LED)
VSS
P6
(Detector)
VSS
|
VDD
And here's the code snippet:
' {$STAMP BS2} ' Target = BASIC Stamp 2 ' {$PBASIC 2.5} ' Language = PBASIC 2.5 ' -----[noparse][[/noparse] 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 ' -----[noparse][[/noparse] Constants ]---------------------------------------------------------- IrFreq CON 38500 ' IR LED transmit frequency ' -----[noparse][[/noparse] 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 ' -----[noparse][[/noparse] Initialization ]----------------------------------------------------- DEBUG CLS, "IR DETECTORS", CR, ' Display heading " FL FR Left Right Back LLight RLight", CR, "----- ---- ---- ----- ---- ------ ------", CR ' -----[noparse][[/noparse] Main Routine ]------------------------------------------------------- main: FOR temp=1 TO 103 GOSUB checkleft GOSUB checkright GOSUB checkfleft GOSUB checkfright GOSUB checkrear Read_Line_Sensors: HIGH LPwr ' activate sensors HIGH RPwr HIGH LIn ' discharge caps HIGH RIn PAUSE 1 RCTIME LIn, 1, lintense ' read left sensor RCTIME RIn, 1, rintense ' read right sensor LOW LPwr ' deactivate sensors LOW RPwr LOOKDOWN lintense, >=[noparse][[/noparse]1000, 0], lintenseb ' 0 = black, 1 = line LOOKDOWN rintense, >=[noparse][[/noparse]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 ' ELSE IF temp>101 THEN temp=1 ' ENDIF ' LOW rled ENDIF NEXT checkfleft: 'Check the front left IR FREQOUT IrLedFL, 1, IrFreq irfl = ~irsensefl IF irfl=1 THEN PAUSE 4 FREQOUT IrLedFL, 1, IrFreq irfl2 = ~irsensefl IF irfl2=0 THEN : irfl=0 : ENDIF ENDIF RETURN checkfright: 'Check the front right IR FREQOUT irledfr, 1, irfreq irfr = ~irsensefr IF irfr=1 THEN PAUSE 4 FREQOUT IrLedFr, 1, IrFreq irfr2 = ~irsensefr IF irfr2=0 THEN : irfr=0 : ENDIF ENDIF RETURN checkright: 'Check the right IR FREQOUT IrLedRS, 1, IrFreq irRS = ~IrSenseRS IF irrs=1 THEN PAUSE 4 FREQOUT IrLedRS, 1, IrFreq irrs2 = ~irsenseRS IF irrs2=0 THEN : irrs=0 : ENDIF ENDIF RETURN checkleft: 'Check the left IR FREQOUT IrLedLS, 1, IrFreq irLS = ~IrSenseLS IF irls=1 THEN PAUSE 4 FREQOUT IrLedLS, 1, IrFreq irls2 = ~irsenseLS IF irls2=0 THEN : irls=0 : ENDIF ENDIF RETURN checkrear: 'Check the rear IR FREQOUT IrLedB, 1, IrFreq irB = ~IrSenseB IF irb=1 THEN PAUSE 2 FREQOUT IrLedB, 1, IrFreq irB2 = ~irsenseB IF irB2=1 THEN PAUSE 2 FREQOUT IRLedB, 1, IrFreq irB3 = ~irsenseB IF irb3 = 1 THEN PAUSE 2 FREQOUT irledb, 1, IrFreq irb4 = ~irsenseB IF irb4=0 THEN : irb=0 : ENDIF ELSE irb=0 ENDIF ELSE irb=0 ENDIF ENDIF RETURNI know I don't depict which connection goes to which on the detector, but rest assured that it is connected properly.
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
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.
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