View Full Version : Are there different IR recievers?

01-28-2006, 11:00 AM
I ordered several IR recievers (#350-00017) .· They look different than the IR recievers that come with the boebot.· How else are they different?·I have set up a simple ir transmitter reciever·pair to detect collision.· The·circuit works perfectly with the IR reciever that came with the boebot.· But the ones I ordered·(#350-00017)·seem to be picking up frequencies from all over the place.· Any suggestions?·

Andy Lindsay (Parallax)
01-28-2006, 11:36 AM
They're about the same. About all I ever do when I swap them is tinker with the resistors in series with the IR LEDs. Reason being, sometimes the black receivers are more sensitive than the silver ones (making the IR pair more far sighted) and other times, they are less sensitive, making them more nearsighted.

To find out how near or far sighted your new receiver is, use a modified version of TestIrPairsAndIndicators.bs2 from Robotics with the Boe-Bot, Chapter 7, Activity #2. Start with the object close to the front of the Boe-Bot. As you move it way, record the various distances that caused each pair to transition from object detected to object not detected. If your new receiver is more sensitive (far sighted), you may need to us a larger resistor in series with that pair’s IR LED to make it less bright. If the receiver is less sensitive, (near sighted) try a smaller resistor in series with the IR LED to make it brighter.

There are some differences in sensitivity to ballast interference between the black and silver receivers. To test this, modify IrInterferenceSniffer.bs2 (same chapter/activity) so that it only tests one receiver at a time. Then, point your Boe-Bot at nearby fluorescent lights. It may well be that your new IR receiver detects ballast interference that the silver ones filter out.

Also test with no fluorescent or IR sources to make sure the detector isn't malfunctioning. If it gives you false detection signals, but the others do not, check your wiring. If your new detector's output is connected to the wrong I/O pin socket (off by 1), it could also explain these symptoms.

01-28-2006, 12:12 PM
This is a problem.· The black IR recievers seem to be synced perfectly with the ballasts in my kitchen.· I have an led that lights when the IR is getting signal.· It lights right up when I walk the circuit into the kitchen.· This is my test circuit for the actual robot that I built today.·

This is discouraging.· I have spent all day wiring up a robot that swifs the kitchen floor.· It's made from the outside of a Robomaid. http://www.therobomaid.com/· I hooked up six ir recievers around the perimiter, and put a stamp in the middle with two servos for drive.· This is my first project where I actually soldered everything. AARGH.· I built the test circuit and was copying it....

Only I would spend all day in the living room building a robot that wont work in the kitchen (the kitchen is the room in the house that doesn't have carpet, thus the room in the house I·need to·"swif")!http://forums.parallax.com/images/smilies/jumpin.gif

·So, is there a way to tone down the sensitivity on the IR recievers so they don't pick up the ballasts.· Either that, or I will have to only run my robot in the dark.· :(

Andy Lindsay (Parallax)
01-28-2006, 12:48 PM
Sorry, I don't know of any cures for strong and persistent interference. If it's not so strong, sometimes, just casting a shadow over the detectors makes it go away. When it's strong and persistent, lights-out is the only solution I know of.

One sure-fire fix would be the Ping))) Ultrasonic Sensor (http://www.parallax.com/detail.asp?product_id=28015)·and optionally the Ping))) Mounting Bracket Kit (http://www.parallax.com/detail.asp?product_id=570-28015). While it's a lot more expensive than the IR detectors, it's also a lot more reliable.· As ultrasonics go, it's very reasonably priced.

Post Edited (Andy Lindsay (Parallax)) : 1/28/2006 5:51:01 AM GMT

Bruce Bates
01-28-2006, 01:11 PM
neoteric -

Try making "blinders" from small pieces of soda straws. This should reduce the effect of the overhead interference. I highly doubt that the ballast inside the fluorescent fixture is causing the interference, but it IS quite possible that the fluorescent lamps themseves can be doing so. Thus, cutting down on the overhead light, should help the situation.


Bruce Bates

Beau Schwabe (Parallax)
01-28-2006, 01:29 PM

Umm... the (#350-00017) is an IR transmitter. Are you sure this is what you ordered?

www.parallax.com/detail.asp?product_id=350-00017 (http://www.parallax.com/detail.asp?product_id=350-00017)

Did you mean the (#350-00014) ?

www.parallax.com/detail.asp?product_id=350-00014 (http://www.parallax.com/detail.asp?product_id=350-00014)

Here is something that you might try on the output of the #350-00014. It is a high pass filter
with a starting cut-off frequency at about 5KHz. At 120Hz ( which is what I believe that fluorescent
lights give off when powered at 60Hz) The attenuation is about -20dB ...At 60Hz this is -28dB

Beau Schwabe (mailto:bschwabe@parallax.com)

IC Layout Engineer
Parallax, Inc.

Post Edited (Beau Schwabe (Parallax)) : 1/28/2006 7:18:26 AM GMT

01-28-2006, 09:08 PM
I am impressed that a Parralax engineer designed a schematic for me at 2AM (I'm on the east coast)· Thanks!· I am truly impressed with the support I get from you folks!
Thanks for the high pass filter.· But I dont think it will change the IR situation.·· It is in fact the ballast that the ir reciever is picking up!· I took the transmitter off the circuit, and the IR reciever still was picking up the ballast!· Even from inside a box.

Oh well, I wasn't so much needing a swiffer as I was learning electronics, and this one taught me a lot.

Solution:· This morning I am putting headlights on it, just for fun, since it will be working in the dark.· I will post pictures when I am done.· For future projects, how do I order more of the silver IR recievers?·

PS, yes, i had the product number listed wrong.·

Beau Schwabe (Parallax)
01-28-2006, 09:51 PM

"I am impressed that a Parrallax engineer designed a schematic for me at 2AM (I'm on the east coast)"
The easy answer to that is that I have a 5 month old .... And weekends are free game. http://forums.parallax.com/images/smilies/smilewinkgrin.gif

"Thanks for the high pass filter. But I don’t think it will change the IR situation. It is in fact the ballast
that the ir receiver is picking up!"

Right, I'll bet if you scope the output from your IR receiver, you will "see" a 120Hz component (Carrier)
with a 40kHz signal riding on top of that. If this is the case, you should be able to use the filter to effectively
remove or minimize the 120Hz leaving only the 40kHz IR signal to deal with.

Beau Schwabe (mailto:bschwabe@parallax.com)

IC Layout Engineer
Parallax, Inc.

01-28-2006, 11:01 PM

Did you try the bot in the box away from the ballast, like in another room? If it is really putting out so much RF as to trigger your circuit, the ballast needs to be replaced. I would lean towards something in your circuit being the problem.

One thing, if you do try blinders as Bruce suggested, I found that a lot of opaque plastics do not block IR. I have had IR detected throught the black plastic of a ball point pen body or cap, for example.


www.madlabs.info (http://www.madlabs.info) - Home of the Hydrogen Fuel Cell Robot

01-29-2006, 01:49 AM
Ok, I understand.· I read your answer incorrectly the first time.· I will try that.· I am a beginner,· are the components a pot, resister, and capacitor?· I will try this...

Its the ballasts.· With the circuit in the box, a circuit with just the IR reciever and led on it, I can turn the light on and off and the led lights up or doesnt.· Works with all three lights in kitchen.· All of which are about 3 mos. old.· (redid my kitchen over the winter)· They are 25W flourescent.· If anybody cares: http://www.lowes.com/lowes/lkn?action=productDetail&productId=36463-16620-36463&lpage=none

Thanks for all the help!

Beau Schwabe (Parallax)
01-29-2006, 03:06 AM

"are the components a pot, resister, and capacitor?"

There are two components, a resistor ( 100 Ohms ) and a Capacitor (1 uF)

The schematic shows a 1V device.... Ignore this, it is part of the simulator
to "excite" the input. If your capacitor is polarized, then the "+" should go
towards the input terminal. "-" should go towards the ground.

Beau Schwabe (mailto:bschwabe@parallax.com)

IC Layout Engineer
Parallax, Inc.

Andy Lindsay (Parallax)
01-29-2006, 04:44 AM

Here is a program (FilterIrInterference.bs2 (http://forums.parallax.com/attachment.php?attachmentid=40228))·that I think will solve the problem.· I even tested it with some blasts from a TV remote, and it still worked.

Here's the trick.· Check each pair a certain number of times.· (I chose 10).· Count the number of times an object is detected.· If it's 10, there's an object there.· If it's less than 10, it's ballast interference.


' -----[ Title ]----------------------------------------------------------
' FilterIrInterference.bs2
' Test IR object detection circuits.

' {$STAMP BS2} ' Stamp directive.
' {$PBASIC 2.5} ' PBASIC directive.

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

irDetectRight VAR Bit
counter VAR Nib
detCnt VAR Nib

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

DEBUG "Testing piezospeaker..."
FREQOUT 4, 2000, 3000

DEBUG CLS, "Detect?", CR

' -----[ Main Routine ]-------------------------------------------------------


detCnt = 0

FOR counter = 1 TO 10

FREQOUT 2, 1, 38500
irDetectRight = IN0
IF irDetectRight = 0 THEN detCnt = detCnt + 1


IF (detCnt = 10) THEN

DEBUG DEC3 ? detcnt



Post Edited (Andy Lindsay (Parallax)) : 1/28/2006 9:51:28 PM GMT

01-29-2006, 05:11 AM
Well, I have completely DESOLDERED the bot, and am now reworking it with Prototyping boards. As a learning experience, I will try both solutions! Thanks for both of them. I am having the time of my life with this stuff.

01-30-2006, 09:53 AM
completed.· Posted in projects.· Thanks for your help.