IR Navigation

ajward

Hey All...

Been experimenting with Bob. Set up the whiskers based navi and it worked pretty well. He could still get stuck if an object was lower than the whiskers. But still, he managed to wander around the apartment for about 5 minutes before he got into trouble!

Next, I set up the IR navi and found two problems:

First, the IR detectors and LEDs are awfully loose in the breadboard and can lose contact, causing the program to continually "see something" in it's path and just keep backing up and turning. Anyone run into this before? I have some 45mm square prototyping boards and, later on, I'll just build a dedicated/soldered IR module.

Second, the IR circuitry seems =way= too sensitive. The back-ups and turns activate with objects up to 24 inches away. Is there someway to dial down the sensitivity? I haven't found anything in the manual that seems to do this.

Tomorrow's project is to try navigating with a fixed Ping))) module. Yeah... fixed will probably be kinda sucky, but still a learning process. (The Ping mounting kit is on the way)

Appreciate any thoughts!!! :-)

Amanda

ajward

Oh... just saw the section about distance measuring with IR! That might be an answer... DOH! Still, if y'all have any advice... please!?

Amanda

Mike Green

You really need to do the experiments in the "Robotics with the BoeBot" tutorial until you understand how the IR distance sensing works. It's pretty straightforward except for the way the FREQOUT statement is used to generate a 38KHz IR signal when the FREQOUT statement frequency doesn't go up that high (it uses 1/2 the frequency and there's enough energy in the 2nd harmonic for things to work). Look at the datasheet for the IR detector and you'll see how the detection threshold varies with the frequency.

ajward

Mike Green wrote: »

You really need to do the experiments in the "Robotics with the BoeBot" tutorial until you understand how the IR distance sensing works. It's pretty straightforward except for the way the FREQOUT statement is used to generate a 38KHz IR signal when the FREQOUT statement frequency doesn't go up that high (it uses 1/2 the frequency and there's enough energy in the 2nd harmonic for things to work). Look at the datasheet for the IR detector and you'll see how the detection threshold varies with the frequency.

Ah yes! Sigh... not sure how I missed that. R(All)TM, eh?
Anyway... thanks Mike! Much better performance. Still too many things that don't get detected, but he managed a 10 minute tour of the apartment. The cramped bathroom did prove to be somewhat of a challenge.

The 4.7k resistor is pretty darned close, tho' a bit lower would be better. But I'll be darned if I can remember the standard values any more.

Amanda

erco

Too sensitive is a good problem to have. MUCH easier to fix than the opposite. Two ways to decrease the triggering range:

1) increase the series resistor to the IR LED, this reduces the intensity of the IR pulses
2) change the IR frequency away from 38 kHz. It's most sensitive at 38 kHz, less so at 37 or 39 kHz, even less so at 36 or 40 kHz., etc...

There's a frequency sweep ranging program in the Boe-Bot manual.

ajward

erco wrote: »

Too sensitive is a good problem to have. MUCH easier to fix than the opposite. Two ways to decrease the triggering range:

1) increase the series resistor to the IR LED, this reduces the intensity of the IR pulses
2) change the IR frequency away from 38 kHz. It's most sensitive at 38 kHz, less so at 37 or 39 kHz, even less so at 36 or 40 kHz., etc...

There's a frequency sweep ranging program in the Boe-Bot manual.

Agreed... more experimentation is needed.

Amanda