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Project logs / OPTI-LOGIC 400LH rangefinder serial protocol determined
I've needed a rangefinder for some surveying stuff (not hugely accurate type of work, just me being lazy and not walking), so I needed something with compass and tilt sensing built in. Plus I wanted one that would save the data. Of course there are few of those, and pricey, so I bought an opti-logic 400LH off ebay in the hopes I could determine how it worked. I thought I would have a reasonable chance at it since the same company makes a module with RS-232 output. After numerous trial and errors, I think I have worked it out.
There is an 11 pin connector that ties the main board in the the pulse generator and sensor sub-boards. Plenty of action on lots of those pins.
I can't work out what most of the are, some are pulse start and maybe even sensor received. I did find one that seemed to be a clock, though it has two positive pulses in groups, and fires a total of 28 pulses. The data sheet for the rs232 module version says the raw output is 0-4095 counts, so 12 bits. I am guessing here that the last 12 pairs are the data clocked out.
Pin for data is the 4th one, pin for clock is the 6th one, with numbers starting closest to battery
The reason it is clocked out is there is a sub-assembly that has an ST processor and a MEMSIC accelerometer to provide the tilt compensation. Data is sent out even if this board is unplugged, but if you swith to mode 2 (horizontal corrected mode) the instrument always says zero (it waits for a response and eventually times out). To do something I chose to "ignore" the first 4 clocks, then sample the data on the falling edge of the first clock pulse out of each two (the data line seemed to always change state on the second clock edge). For the shown segment, the value is 000001100011 MSB first (99).
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I plotted the decimal result versus feet displayed on the lcd of the 400LH and the graph is attached. The correlation is not totally perfect because I used each distance measurement, because in mode 1 (and 2, I did not test 3 or 4) on the 400LH, there appear to be a total of 8 laser firings which are then averaged to get the final value.
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Hope this is useful to some.