IR sensor tuning?

[upand_at_them]

I was at a line-following robot competition recently and one of the contestants mentioned that he tuned the IR detectors to match the emitters. I asked if he meant that he was pulsing the emitters, but he said no.

I know about tuning for a carrier frequency, like 38kHz, but had never heard of tuning for the light frequency. What was he doing?

 

[Mr RB]

I don't think he would be talking about tuning the frequency of the emitters.

It is very common to "tune" the emitter-receiver pair in intensity, either by adjusting the distance to the reflected surface or by adjusting the LED current or receiver DC biasing. They need to tune them for different coloured surfaces or different room lighting at events.

 

[upand_at_them]

Well, I remember he said that he had to tune them and it took him a while to get the frequencies right. And he had a separate pot to tune each pair. So the only thing I could think of was that he was indeed pulsing the emitters at 38kHz (or somesuch) and had to tune the detector circuits to match the frequency.

But you lose detection intensity when you do this, right?

What is "receiver DC biasing"?

I'm not sure if he was using IR detectors or photocells for the receivers.

 

[Mr RB]

I really doubt he was pulsing the LEDs or that adjusting the frequency of the pulses LEDs would make any difference.

You also said he said "he was not pulsing the emitters".

If he specifically said he was tuning a frequency he might have been tuning the frequency that his software checked the sensors, so if the line had tight curves he might have increased how often his bot checked the sensors. Really it's all speculation, you should be asking him not us.

"Reciever DC biasing" is usually done by a small trimpot in series with the receiver photodiode, basically it adjusts how much infrared light is needed to make the receiver produce a voltage level output that the bot can detect. They adjust them for different floor colours etc.

 

[upand_at_them]

Yeah, I'd ask him more about it, but I only see him once a year at that competition. Thanks.