IR detector

[zs]

Hi everyone,

I'm trying to build my 1st robot that uses IR sensors to avoid collision with obstacles at the same time that travel from one IR beacon to another IR beacon. My question is how can I use phototransistor to build IR detector to detect only the beacons' IR without interfering with the obstacle sensors? thanks.

[dunk]

make sure only one IR source is switched on at any one time.
if you have you beacons switch on for a set time and then off for a set time, have the robot scan for the lit beacon.
once your robot knows the timing sequence of all the beacons it can see it is free to use it's own IR emitters in the "dark" phase.

make sense?

dunk.

[zs]

I'm using Sharp IR sensors that have emmitter and detector altogether to avoid obstacles and are "on" state all time. The two IR beacons transmitt IR @ different frequencies continuously, there is no "on" "off" state. My Robot's mission is to search for the first beacon and lock to that beacon and to reach there. Once it reached the 1st beacon it will start searching for the second beacon and do the same thing. My problem is how can I use IR detectors only to detect IR beacons and direct the Robot to the detected beacon? I guess I made my question a little bit clearer this time. I hope you guys will help me out. Thanks

[frank26080115]

this won't require timing
switch on and off the robot's emitter once every few milliseconds
have the beacons only turn on it's own emitter when it detects no emitted ir light from the robot, at which point, as the robot knows its own emitter is off, it will know the only source of ir is the beacon. once the robot turns on its own emitter, the beacon shuts off, and as the robot knows its own emitter is on, the only source of ir is an obstacle.

if all the emitters have the same brightness/range there should be no problem

also to judge between which beacon, have one beacon output ir at 38khz so only a 38khz reciever module can see it, if it can't but the light is there, it means it is looking at beacon A, if the module can see it, it means the robot is looking at beacon B

[Ro-Bot-X]

I would use Sharp IR distance sensors for obstacle avoidance.
I would use the beacons on the same frequency (say 38kHz), but transmitting different code, with a delay between them. There are several ways to do this.

This way the robot can detremine the location of each beacon by the code received. If you have 3 beacons you can triangulate the position of the robot in the field.

[zs]

You guys have been great help, Thanks. Do you mind telling me a couple of ways how to make the beacons transmit different code? One more thing, I'm thinking of building the beacon myself, but are there beacons in the market that transmit IR in omni-directional? I really appreciate your help.   

[zs]

Hi,
Hence no one answered my previous question, I have another one. How can I direct my Robot to the 1st IR Beacon while avoiding obstacles on the way? I want my Robot to know where its 1st destination is when it start moving and detect IR light from the 1st beacon. Any Idea how to execute this task? Help my Robot so that it can get to its destination safely  . Thanks

[Ro-Bot-X]

The beacons can be made using a microcontroller that sends serial data using IR, over a carrier frequency like 38 or 40 kHz. One beacon will have the electronics on board and the others will be connected by wires. Or, if you need them to be wireless, you will need each beacon to have it's own microcontroller, IR emitter and a receiver. When you power them up, the first one will start to "beep" in IR a message, let's say 100, every 30 ms. The second beacon will listen for message 100 and after it receives it, will wait 10ms and send i's own message, let's say 150. The third beacon will listen for the message 150 and after iit receives it, will wait 10 ms and send it's own message, let's say 200. The emitter can be an array (circle) of IR LEDs connected to a transistor, connected to the microcontroller. This way the signal will go in each direction. The robot will have the receiver mounted on a servo to be able to scan the area in front of him to find the first beacon (will listen for message 100) then drive to it, using the Sharp distance sensors (wich don't interfere with the IR messages) to go around obstacels. Each time an obstacle has been bypassed, the robot will scan for the beacon again, to make sure it has the corect heading. After arriving at the first beacon, it will scan for the second beacon (listening for message 150) and drive towards it and so on.

[zs]

I like the idea of mounting the IR detector on the servo to search the IR beacon, but how does the robot knows if the beacon is on the right, left or in the front? There gotta be some way to determin the location of the robot relative to the beacon or vice versa. Any idea? Thanks.

[Admin]

I have another one. How can I direct my Robot to the 1st IR Beacon while avoiding obstacles on the way?

Remember that the objects cannot block line of sight between the robot and beacon - IR can't pass through most objects.

I plan to write up a pathfinding tutorial sometime this summer so your robot can go through mazes and do mapping and object avoidance, etc.

The simplest way to go around an object:
Step 1 - robot goes toward beacon
Step 2 - robot comes into contact with blocking object
Step 3 - robot swaps to wall following algorithm
Step 4 - robot follows wall of object until no object is between robot and beacon
Step 5 - go to Step 1

This algorithm is far from being efficient or flawless, but its the easiest possible and best for a beginner to start off with.

Good luck!
John

[zs]

Thanks for the pathplanning algorithm. I did read some literature about pathplanning algorithm but it's beyond my scope of understanding. Anyways, I searched the internet and have found digital compass that can help the robot to navigate. I just wanted to share my findings with you, guys. I'm still working on how to incorporate the compass with the IR detectors. Please, keep posting any ideas you may find is helpful to make my robot's journey easier to find the two beacons( it's destination)  . Thanks, you guys are the best.

[Steve Joblin]

Pololu sells a great IR Beacon at a very good price... check out http://www.pololu.com/products/pololu/0701/ for details.  They provide details on how it works, a schematic, etc!

[zs]

Thanks for the link. Here's what I wanted to do. I'm gonna use PNA4602M IR detector mounted on a servo, to detect a wide range for IR. Once it detected the IR, the robot starts moving and the digital magnet guides the Robot toward the detected IR beacon( I have to figure out later how to do this part ). When it sees an obstacle the sharp IR obstacle avoidance sensor will divert the robot away from the obstacle and the digital magnet once again will guide the robot to the IR beacon until it reaches to the 1st beacon, then it stops wait for 10s or so and start searching for the 2nd beacon. Now, my question is how can I tell the robot to stop when it reaches the intended beacon? I'm thinking of a phototransistor that increase the out put amplitude as the robot gets closer to the IR beacon and send message to the micro controller to stop the robot. what do you guys think? Do you think it works?  .thanks

[Admin]

I'm thinking of a phototransistor that increase the out put amplitude as the robot gets closer to the IR beacon and send message to the micro controller to stop the robot.

Ive done this for many types of sensors and it works great. (it requires a one time calibration)

[zs]

Here's my unsolved problem with the IR beacons. I have two IR beacons that transmit 3KHz and 7KHz IR signal. I want the robot's IR detector (PNA4602M 38kHz ) which is mounted on servo to detect only the 3KHz IR light first when searching for IR light and get there first. And then start searching for the 2nd, the 7KHz IR light and start heading to that beacon. Now, I can't code the IR beacons with different codes the only specification is that the beacons have different frequencies, 3 KHz and 7 KHz. My question is how am I going to make the detector to pick 3KHz first then the 7KHz wile this detector module can be used for applications operating at 38KHz? Thanks.

[Ro-Bot-X]

The PNA4602 sensor has the best results working with the 38kHz signal. It can receive a little lower and higher frequencies like 36kHz and 40kHz, but from a shorter distance and sometimes with signal loss. It will NOT work with such a low frequency as 3kHz or 7kHz. You will need a different sensor.

Take a look at the remote controll stuff this store has: http://www.rentron.com/PicBasic/RemoteControl.htm

[zs]

Thanks for the link. Unfortunately, I couldn't find 3Khz and 7KHz IR detector. Any suggestion on how to build IR detector just for these two frequencies? I really appreciate your help.

[dunk]

i don't think you will find off the shelf 3Khz and 7KHz IR detectors.
not sure how you would build one using analogue electronics.
not that it would help anyway as the different beacons would cause interference with each other.

if i had to had to use this approach i'd probably use an IR photo diode with a microcontroller's analogue port and look for changes in the amount of IR over time and try and spot the different frequencies in software.
i would definitely pick 2 frequencies further appart than 3Khz and 7KHz. the 7KHz beacon will only go through 2.33 oscillations before the 3Khz beacon changes and throws your readings off.

in my opinion you would be far better finding a way to make sure only one of the beacons was lit at a time.

my 2nd choice of methods would be to transmit some sort of signal in the modulated IR. look for circuit diagrams for IR remote controlls.
there are a few chips out there that do all the hard work for you. for example http://www.sunrom.com/media/datasheet/3000-1012.pdf
with this approach you will still get bad results when 2 beacons appear at the same brightness.

if you are going to continue with your current plan, try to build circuits that operate at very different frequencies.
for example 36KHz, 0.36KHz and 36Hz.
this way you will be able to identify and filter out 2 of the beacons while looking for the 3rd.

dunk.