Power

Turning the Unit ON - Obtaining a Range Measurement

1. Manually:

By pressing the  START button to obtain a single measurement (Single update mode) or can be set to take continuous readings (Continuous update   mode) by installing the DATA IN adapter plug.  Plugging in the adapter plug   prior to turning the unit ON results in readings being taken immediately following power ON without pressing the START button.
 
2.  Computer:

A computer generated "start" pulse signal (any positive going pulse) can be sent to the LRF by a remote computer to initiate a reading (Single update mode).  Continuous update mode can also be achieved by sending the appropriate command (see table A2 for a list of the available commands).
 

LRF Messages

    READY        Indicates the unit has passed its self-test and can begin taking reading.

    *                    Replaces the decimal point in a range reading to indicate the battery  is low
                          (below 9.5V).  Appears on the display as well as the remote
                          terminal.

    <                   Appears to the left of the range reading indicating the over 12.5% of the shots were
                         invalid (drop-outs).  This is ignored in my present  program implementation.

    <<<<             Appears in place of a reading (both on the display and the remote terminal)
                         indicating an accurate reading could not be taken.

    ERROR        Appears on the display when there is a problem with the unit..

2.  Beeper

• 1 SHORT BEEP        Normal reading obtained.
• 2 SHORT BEEPS      Valid reading however, more than 12.5% shots were drop outs. .                                  A '<' also appears on the display.
• 1 LONG BEEP           Unable to take an accurate reading.  '<<<<' also appears.

Remote Terminal Connection

Several of the solder connections on the D9S became loose and were re-soldered.  To avoid any wiring mix-up, table A1 below shows the correspondence between colour wire coming from the six pin circular connection and the pin number of the D9S connector

Control Commands via a Serial Connection

The commands can be sent at any time and in any order however, all the commands must contain a Carriage Return (CR) as their last character.

In order to process each command, the LRF requires a certain time delay.  According to the Optech manual, this delay should be 200usec, however, I discovered the delay time required is about 1ms.
This does not affect the proper functioning of my program since commands are issued once only prior to obtaining any readings.

Description of the Serial Port Data Transmitted

Valid Reading:

Three characters representing the whole portion of the reading, a character representing an ASCII period
followed by two characters representing the decimal portion.  When the whole portion of the reading requires less than three digits, the character(s) not used are assigned SP.

Drop Out Reading:

Four ASCII characters representing '(', followed by two SP characters.

NOTE:    With a terminal connection to the LRF, upon turning the LRF ON, the ASCII characters
                representing the string 'READY' are sent to the terminal.

 LRF Specification

• Distance readings can range from 0.2m to 100m.  For our purposes, a range between 0.5m and 15m was used.  I have also found trying to obtain a distance reading less than 0.2m results in a drop-out (indicated by '<<<<').

• An accuracy of 10cm is achieved between the temperature ranges of -20^oC and 50^oC.

• The FAST/SLOW switch sets the time taken to obtain a reading by controlling the number of shots being averaged (each distance reading is an average of all the shots fired in order to reduce random errors).  Table A3 below illustrates the relationship between the number of readings per second and the shots per reading.

• Two readings/second are obtained in the SLOW setting, while eight readings/second in the FAST setting.  With a serial connection many more shots/reading settings are permitted.

• With a serial connection, during power ON the unit will respond to the SLOW/FAST setting, however, this can be changed by sending the desired shots/reading at any time.  Valid settings can range from  1-9999 and must be followed by a Carriage Return ("\r").  For example, for a setting of 150 shots/reading, "150\r" should be sent.

• Decreasing the number of shots/reading decreases the time to obtain a reading, however, it also reduces the accuracy of the distance readings.

NOTE:
It has been observed that the relationship between the shots per reading and the number of readings per second provided with the LRF operating manual is erroneous.  According to the manual, the SLOW setting of two readings per second corresponds to 1000 shots per reading while the FAST setting of four readings per second corresponds to 150 shots per reading.  This is clearly not the case.  With a shots per reading setting of 1000, a reading was obtained approximately every five seconds (easily timed using a stop watch) while a setting of 150 resulted in a reading approximately every two seconds.  In order to determine the correct settings, experiments were conducted where a number of readings were obtained (50 readings) at a particular shots per reading setting.  The time between consecutive readings (in microseconds) was measured and an average was determined.  From this average the number of readings per second was derived.   Table 2.3 above illustrates the results of several such experiments.  Although the readings per second values are an approximation, they are accurate enough for our purposes.

4.  Environmental Conditions

• The LRF was used primarily during the day although I have experimented with it during the night with a minimum amount of available light and have found it works fine.

• I have not had the chance to use the LRF during a snowfall or rainfall although according to the owner's manual, it should work fine.

• Windows pose a problem with object recognition since the LRF will not measure the distance to a window. Windows do not reflect the signal instead the signal passes through the window and a measurement of an object beyond the window is taken.

• "Model G150 Range finder User Manual" Version 1.1, May 1991
• "Model G150 Release Notes" June 11 1992

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Fax: (416)661 - 4168