Great. Now I have a winter project.
Thanks for the information. I suspected intensity, temperature, and ambient light(?) might be factors. It is easy to see how echo intensity might be corrected for. Is temperature a factor too?
John
John,
The method used is:
At TX time [about 250pps] the LD163 30Watt is lased, using a transistor in avalanche mode, for a pulse period about 25nSec, a TX F/F is set.
The TX F/F setting enables a high linearity ramp down voltage, as the echo is detected the TX F/F is reset and the ramp voltage is run upto a zero detect comparator.
The ramp run up time is 50 or 100 times longer than the ramp down rate.
During the ramp up a high speed xtal clock is gated into a counter and stopped at zero crossing of the ramp.
By choosing the xtal freq as multiple of 15Mhz. [ assuming the laser beam travels at 300,000,000 mtr/s , round trip of the pulse is double the range]
you can get a direct count of the range.
If you capture the peak value of the returned echo and digitise it using a8 bit high speed adc you can use this 8bit value as an address pointer to the signal strength table and adjust the correct measured range.
The cal table resides in non volatile memory and is created during calibration in production.
The range spec for the laser is 5000mtrs from cooperative targets with a resolution of 0.1mtr.
If you want more info, just ask.