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Speed Measurement System

A DIY Gatsometer with infra-red light barriers

Speed Measurement System
The light barrier system described in this article allows accurate measurement of the absolute speed of model cars, planes and other moving objects. In education and training programmes, the system forms a perfect contactless speedometer. Over to you to football and golf fans to see who has the meanest ball kick or club swing.Light barriers systems are around us in more situations than you would expect. Unnoticed, they do their job scanning items at the supermarket checkout, detecting vehicles in parking lots, video tapes in VCRs or persons entering or leaving buildings. Usually, infra-red light is employed because it is invisible to the human eye and ensures a high degree of immunity against interfering light sources.
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Gerber file

CAM/CAD data for the PCB referred to in this article is available as a Gerber file. Elektor Members can exclusively download these files for free as part of their Membership. Gerber files allow a PCB to be produced on an appropriate device available locally, or through an online PCB manufacturing service. Elektor recommends its business partner Eurocircuits as the company of choice for its own prototypes and volume production in selected cases.

Resistors:
R1,R2 = 4kOhm 7
R3 = 10kOhm
R4,R5 = 100kOhm
P1 = 10kOhm preset
Capacitors:
C1 = 10µF 16V
C2-C5 = 100nF
C6,C7 = 15pF
Semiconductors:
IC2 = 7805
IC3 = 87LPC762, programmed, Publishers' order code 010206-41
Miscellaneous:
K1 = 9-way sub-D socket (female), angled pins, PCB mount
K2 = 14-way SIL pinheader
S1-S4 = pushbutton
S5 = on/off switch
X1 = 6MHz quartz crystal
LCD dot matrix display, 1x16 characters, 44780-compatible with connections in top left hand corner
2 combinations of IR-Sender PIE-310 and IR receiver PID-310 (Kodenshi, Farnell #139-865)
4 module connecting cables, Farnell #310-0728
PCB, Publishers' order code 010206-1
Disk, contains source code and Hex files, Publishers' order code 010206-11 or free download
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