Lap Triggers. Application Note. McLaren Electronic Systems McLaren Technology Centre Chertsey Road Woking Surrey GU21 4YH UK

Transcription

1 McLaren Technology Centre Chertsey Road Woking Surrey GU1 YH UK McLaren Electronics Inc. Suite 11 Bostick Building 9801 West Kincey Avenue Huntersville NC 8078 USA Copyright McLaren Electronics 01 Revision Date: 0 Feb 009 Page 1 of

2 Optical Lap Trigger System The optical system consists of the LTX-00 transmitter and the LRX-00 receiver. The LTX-00 transmitter has an array of infra-red emitters which produces a focussed beam to give an operating range of about 0m in optimum conditions. LTX 00 is powered by an external battery connected via a flying lead. LTX-00 transmits one of codes, selected by switches inside the unit. The codes are split into 1 groups and each group is split into 1 channels. The LRX-00 receiver is set, by an internal switch, to respond to only one of the 1 groups, signals from other groups are ignored. When a matching group code is detected, the LRX-00 outputs a TTL level pulse as well as an analogue voltage to identify which of the 1 possible transmitter channels was transmitted by the LTX-00. An LED on the rear of the LRX-00 indicates when a transmission from the selected group has been detected. LRX-00 can discriminate between up to 1 different lap triggers, transmitting different channels, around the track. For example, transmitters could be placed on the start/finish line, in the pit lane and at other key locations to create timing split points and speed traps. LRX-00 is a compact, cylindrical unit that can be readily accommodated on a car. It has a wide dynamic range and integrated filters to minimise interference from sunlight or other heat sources. It should be mounted in the car in such a position that it has a clear and direct view of the transmitter as it passes. If a window is used, it must be transparent to infra-red at 87nm. If possible, the mounting should be in a location which does not get wet or dirty. Two variants of the LRX-00 are available which either combine the timing pulse and channel identification voltage on a single output or provide two separate outputs. In each case the channel identification voltage has 1 of 1 values according to the channel code received from the transmitter. In the Combined Output Version a short (10ms), TTL level, active high, digital pulse is superimposed on the channel identification voltage when a valid lap-trigger signal of the selected group code has been received. In the Separate Output Version the timing output is a short (10ms), TTL level, active low, digital pulse which indicates that a lap-trigger signal from the selected group has been received. The channel identification voltage is output continuously on a separate wire and only changes if a signal is received from a differently coded transmitter using the same group. Copyright McLaren Electronics 01 Revision Date: 0 Feb 009 Page of

3 Setting up the LRX/LTX-00 system Transmitter LTX-00 needs to be set up to send a code which corresponds to the desired group and channel. The settings are by a DIL switch inside the unit. The switch is accessed by removing the rear lid of the unit (held by four screws). The switch is at the bottom of the board near to the tripod mount and is marked with the ON position and the individual switch numbers. When replacing the lid, use a new O-ring and sealing washers. Switches 1 to define a group number (from 1 to 1). Table 1 lists the switch positions for each group. Switches to 8 define a channel number, which is used to identify the LTX-00 to the receiver. LRX-00 generates an analogue output corresponding to the channel number. Table lists the switch positions for each channel as well as the LRX-00 channel identification voltage. To avoid interference, ensure that no other team at the circuit is using the same group as you. Receiver LRX-00 needs to be set up to receive the same group as is being transmitted by the LTX-00. Remove the screw on the back of the receiver with an Allen key and use a small Phillips screwdriver to turn the recessed PCB mounted switch inside. Rotate the switch clockwise to select from group 1 to 1. The switch has no stop, the two arrows on the back cover show the allowable movement. Set an LTX-00 transmitter to the desired group and point it at the receiver. Rotate the switch slowly until the LED on the receiver flashes at approximately 1Hz. This indicates the receiver is correctly set to receive that group. Replace the cover screw with its sealing washer. Table 1: Optical Transmitter Group Setting Group Switch 1 Switch Switch Switch 1 Off Off Off Off Off Off Off On Off Off On Off Off Off On On Off On Off Off Off On Off On 7 Off On On Off 8 Off On On On 9 On Off Off Off 10 On Off Off On 11 On Off On Off 1 On Off On On 1 On On Off Off 1 On On Off On Copyright McLaren Electronics 01 Revision Date: 0 Feb 009 Page of

4 Table 1: Optical Transmitter Group Setting Group Switch 1 Switch Switch Switch 1 On On On Off 1 On On On On Table : Optical Transmitter Channel Switching Channel Channel Identification Voltage (V) Switch Switch Switch 7 Switch 8 1. Off Off Off Off.87 Off Off Off On.01 Off Off On Off.77 Off Off On On. Off On Off Off.187 Off On Off On 7.91 Off On On Off 8.7 Off On On On 9. On Off Off Off On Off Off On On Off On Off On Off On On 1 1. On On Off Off On On Off On On On On Off On On On On Microwave Lap Trigger System The microwave lap trigger system consists of the LTX-10B transmitter and the LRX-10B receiver. In the LTX-10B transmitter, a specially selected horn antenna gives a focussed narrow beam of microwaves at 10.GHz. Careful choice of the E and H plane pattern minimises multipath effects caused by scattering from the ground and other objects. The LTX-10B has an internal sealed battery that provides approximately eight hours operation when fully charged. An external battery can be connected for longer operation. LTX-10B modulates the transmitted microwave beam at one of possible frequencies, allowing six teams to each operate up to six LTX-10Bs at the same track. The group code for each team is set at the factory by an internal switch. An external position rotary switch selects a channel which allows the receiver to discriminate between different transmitters on the same group code. LTX-10B has a key locked power switch, preventing accidental deactivation. The LRX-10B receiver is a small X-band microwave module with a specially-designed waveguide antenna in a small, lightweight assembly, ideally suited for car mounting. It can be mounted by applying self adhesive hook and loop or Dual- Lock type fasteners to any face other than the front. The slotted waveguide antenna covers the entire front face of the LRX-10B. The antenna is most sensitive perpendicular to the front face which should have an unobstructed line-of-sight path to the transmitter. The receiver may be mounted behind a window which is transparent to radio at 10.GHz. Kevlar, glass-fibre, polyethylene and PTFE Copyright McLaren Electronics 01 Revision Date: 0 Feb 009 Page of

5 are suitable window materials. Carbon-fibre or metal are unsuitable. To prevent distortion of the RF beam shape, the thickness variation across the RF window should be less than 0.mm. Maximum detection range is approximately m. To achieve this, it is important to match the polarisation of the transmitter and receiver antennas to within ±0. If the transmitter is mounted with its feet downwards, then the receiver must be mounted with its long axis horizontal. LRX-10B outputs trigger pulses as it passes through the beam of an LTX-10B transmitter. The pulse repetition interval is inversely proportional to the modulation frequency and the amplitude of the pulses is proportional to the strength of the received signal. LRX-10B detects any of the channels transmitted by LTX-10B and does not need to be set up. The transmitter channel is identified from the Pulse Repetition Interval shown in Table. Table : Microwave System Settings Transmitter setting Receiver Output Factory Switch Group Setting Rotary Switch Channel Setting Pulse Repetition Interval µs Copyright McLaren Electronics 01 Revision Date: 0 Feb 009 Page of

6 Table : Microwave System Settings Transmitter setting Receiver Output Factory Switch Group Setting Rotary Switch Channel Setting Pulse Repetition Interval µs Copyright McLaren Electronics 01 Revision Date: 0 Feb 009 Page of