Benm
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- Joined
- Aug 16, 2007
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Because of the receiving end of the system... the ambient light from the outside
world has a negative effect on the receiving sensors ability to see small laser level
variations.
By modulating the laser... like a carrier wave... and demodulating it it at the
receiving end.. it will easily block out unwanted signals (varying light levels)
and more easily see the true ON/OFF data...
For example... using an IR LED and IR photodiode with no modulation... just pulsed
on and off at 100 hz I get a detection distance of 2"-6"...
But when the same IR LED is Modulated at 40kHz and the Photodiode Demodulates
the ON/OFF pulses at the same power levels I get a distance of over 30 feet.
Jerry
You're absolutely right there, using a carrier will do a lot to tackle noise problems and interference. Problem is, if we're aiming for 10 MBit, the carrier would have at least an order higher (if you wanted to do FM and demodulate with a PLL), so you're looking at modulation and demodulation in the 100 MHz+ range.