I would like to recreate a infrared concept used by in the vacuum cleaning robot's charging station.
I would like to use 3 infrared transmitters all in same wave length and transmit a synchronized bit pattern (on, off, gap duration).
All the led's will in sync and sending a fix and repetitive sequence e.g.:
Led A would send 11110001
Led B would send 11110010
Led C would send 11110100
The next step is to assign each Led a max Transmission distance e.g.:
Led A => max 4 ft
Led B => max 8 ft
Led C => 12 ft
Theoretically speaking a IR receiver would get:
11110100 from 8-12 ft range
11110110 from 5-8 ft range
11110111 from 0-4 ft range
The question is, how can i limit an IR distance ? It's not necessary to be exact intervals, instead we can use relative fractions 1, 1/2, 1/4 the idea is to know the distance from the base.
Do i need different transmitters, if yes what i need to take in consideration in the datasheet ?
Changing the frequency e.g. 38Khz does increase or decrease the distance ? But having different frequencies does not affect the receiver capture ?
Thanks
Regards,
Tiago.
Best Answer
You can limit the distance by lowering the LED current (or lowering its ON time compared to the OFF time), or by 'mismatching' the signal with what the receiver expects (change the frequency, saturate the receiver by continouus transmission, arrange for interferring signals), but you can't use that to set a reliably reproducible distance limit.
Think of it a speaking soft. How soft do you need to speak to make people hear you at 10 ft but not at 20 ft?