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Hot Lap Performance Monitor Operating Instructions


Table of Contents




The Hot Lap Performance Monitor (21711) consists of four parts:


Microcomputer (21640). The controller for the system. All onboard parts connect to this box with telephone-type cords. Their connections are clearly marked. The four parts are: wheel sensor, with a 4-conductor RJ-8 plug, steering wheel switch, (4-conductor), Hot Lap receiver (6-conductor, RJ-11) and Hot Lap Display (6-conductor) Additionally a 9-pin D connector provides serial input/output for an IBM PC or compatible and open collector direct connection for a data acquisition system. The system power switch is located on the microcomputer, as are the system MODE and START switches. In existing Hot Lap systems, these functions are on the display. The microcomputer takes over the functions, and existing switches can be eliminated. A switch on the front panel selects the function to be displayed: LAP TIME, PERFORMANCE, or SPEEDOMETER. Function selection can be made at any time.


Wheel sensor (21630). A small (1-1/4" long, 3/8" OD) pickup that permanently mounts on a nonrotating suspension member near the inside of the wheel rim, preferably on the right front wheel (to avoid wheel lift on cars that lift). The sensor detects the presence of a magnetic field provided by a small, very strong magnet installed on the wheel rim. Can also be mounted on the drive or CV shaft on cars that do not spin on acceleration) The sensor is connected to the microcomputer with a telephone-type cable. A battery in the microcomputer powers the sensor through this cable, and the sensor sends information back on wheel turns. A calibrate mode (P3) is provided to verify that the sensor detects the magnet.


Early Wheel sensor (Replaced with Model 21630 Sensor) A postage stamp-sized pickup that performs the same function as the 21630. Sold with earlier systems.


Magnet Glued to one of the rims, this magnet provides the field for the wheel sensor.


Steering wheel switch (21616-4). A normally open momentary contact switch on the end of a telephone-type curly cord. This switch is designed to mount through any existing hole in a steering wheel spoke. The switch operates according to the position of the toggle switch as follows:
LAP TIME - simulates the signal normally provided when the receiver sees the transmitter.
PERFORMANCE - selects the most recently completed lap as the reference lap.
SPEEDOMETER - instructs the system to memorize the speed of the moment the button is pressed.


The display to the driver is presented on the 21615 or 21618 Hot Lap display, or on a 21617 Performance Monitor Universal Display.


Note: The 9-volt battery powering the onboard portion of the system is in the microcomputer. When connecting to existing Hot Lap timers, remove the battery in the 615 display or remove the 619 battery holder. The reason: if two batteries are in the system, the stronger one will try to charge the weaker one, shortening battery life.






Mount the sensor to a nonrotating suspension member near a wheel rim in a location that faces either the flat or the grip edge of the rim. On rear wheel drive cars, the right front wheel is the location of choice. The sensor must be solidly mounted.


Any structural member such as a shock tower, A-arm, or brake part can be used as a mounting point. Brackets that you fabricate should be strong enough to hold the sensor free from vibration that could move it into the path of the rotating magnet and damage it. The sensor should clear the magnets by 1/4 to 3/8 inch. Closer than 1/16 inch could result in improper operation and damage to the sensor. Farther than 3/8 inch could result in the sensor not detecting the magnet. Use the gage provided with the sensor to assure that the distance is greater than the minimum.






A rare earth magnet is provided with the Performance Monitor system. It has been selected for its strong field properties, small size, and light weight. The magnet is polarized and will trigger the sensor in only one direction. The colored dot should face the sensor. Use the calibrate mode (P3) to check for proper direction before gluing the magnet in place.


Use epoxy glue to attach the magnet to the wheel rim. The preferred location to mount the magnet is on the inside flat of the rim. Here, centrifugal force tries to drive the magnet harder into the rim and hold it firmly. An alternate location for the magnet is the grip edge of the rim. Here, centrifugal force will try to throw the magnet outward, and it must be both epoxy glued and covered with duct tape.


Check your sensor/magnet installation. Put the system in P3 mode and press START. Slowly rotate the wheel moving the magnet past the sensor. The LCD display should indicate a change from - to 0, or 0 to -. If the reading changes twice as the magnet moves past it, i.e. from 0 to - and back to 0, the magnet is mounted backwards and the sensor is too close to the magnet. Reverse the magnet and move the sensor away from it.






The microcomputer is powered by a 9-volt battery accessible through a door in the back of the unit. The battery is not supplied. Use alkaline batteries. Mount the box within reach of the driver so that the batteries can be changed easily.






The microcomputer connects to the Hot Lap receiver and the display. The receiver advises the passage of a lap. The display shows either LAP TIME, PERFORMANCE, or SPEEDOMETER as selected by the driver. The microcomputer also connects to a magnetic sensor mounted to a nonrotating structure on one of the front wheels.. A magnet mounts to the wheel rim in line with the sensor. On system setup, you set the distance the car travels in one wheel revolution with P5 (tire size factor). Each time the sensor detects the magnet, it sends a signal to the microcomputer, which measures the time between magnetic pulses to determine the distance the car travels. It then converts this data to speed.


NOTE: The following functions change when the Hot Lap timer is used with the Performance Monitor: € Retrigger time was 5 sec. fixed; it is now adjustable from 1 to 59 seconds. € Memory was 60 laps; it is now 99 laps. € Memory recall of laps was in order; it now displays the fastest lap, then lap recall in order. € Data acquisition output signal was logic level; it is now open collector direct connection. € A new low and dead battery indication is provided. € Maximum lap time was 5 minutes, it is now 4 minutes.


A toggle switch on the microcomputer front panel selects the function to display.


Lap Time Function Set the select switch to LAP TIME position to perform functions described fully in the timer system operating instructions. When first turned on, the display shows all dashes until the car passes through the beam, when it changes to lap 01 and its time.


Performance Function Set the select switch to the PERFORMANCE position to compare current track position to a reference lap and display a bar graph of the relative position. The system monitors the number of wheel revolutions and displays the difference between current track position and reference position on a bar graph in view of the driver. If the car is further down the track at the current time than it was on the reference lap, a bar graph grows in the FASTER direction, in proportion to the amount faster. If not as far, the bar grows in the SLOWER direction. Bar graph sensitivity is adjustable with preset P6.


When first turned on, the display is blank except for a colon in the center. To begin the comparison process, press the steering wheel switch to enter the lap just completed into memory as the reference lap. The performance function updates each time the car passes through the infrared beam, and all succeeding laps are compared to the reference lap.. A "quick look" of lap time automatically replaces the bar display for two seconds of viewing each lap as the car passes through the infrared beam.


When the driver completes a faster lap, becoming the lap to beat, the reference lap can be changed to the lap just completed by pressing the steering wheel switch. In fact, a reference lap stored in a PC from a previous day can be re-entered into memory.


Speedometer Function Set the select switch to SPEEDOMETER to display and record speed. Pressing the steering wheel switch at any time instructs the speedometer to memorize the speed of the chosen points on the track. When first turned on, the display shows the car's speed. If the speedometer is asked to memorize a speed in this lap, it will log it as lap 0.


Automatic speed recorder function Regardless of toggle switch position, the system continuously measures and records lap speed and memorizes when speed increases or decreases. This function produces the information used by the Computer Interface Data Analyzer program to draw graphs of the car's speed. The information indicates lap numbers and speed change events. Up to 500 combined lap and speed changes can be recorded.






A switch on the side of the microcomputer turns all onboard system elements on and off. A 9-volt battery is installed inside the microcomputer via a sliding door in the back. The Performance Monitor is customized to your car and your preferences with the presets described below. Two pushbuttons on the side of the Microcomputer labeled START and MODE activate the presets. The presets can be entered manually or with the Computer Interface. To select a preset manually, press MODE for two seconds. P1 appears in the left two digits.


P1 Recall recorded lap times.
Display format is XX X:XX.XX
The first 2 digits are the lap number
The last 5 digits are min.sec.hundredths
Records the last 99 laps
Starts at best time, then goes to lap 01


Recalls lap numbers and times. Press MODE, and P1 appears, with the fastest time and its lap number. Press and release START to display lap 01 and its events. The display blinks to indicate that the system is reviewing. Press and release START to advance to lap 02. Continue pressing START to review each lap. When START is pressed on the last timed lap, the display returns to lap 01. To quickly sequence through all recorded laps, hold START down. Press MODE to cancel review mode and return to normal operation.


P2 Recalls manually triggered speeds.
Display format is XX XXX
The first 2 digits are the event number
The last 3 digits are the speed
Triggered by steering wheel switch
Stores up to 99 triggered events


Press and release MODE twice. P2 and the event number and speed appear. Press and release START to display event 02 and its speed. The display blinks to indicate that the system is reviewing. Continue pressing START to review each event. When START is pressed on the last recorded event, the display returns to event 01. To sequence through all recorded events, hold START down. Press MODE to cancel review.


P3. Calibrate mode.
Display format is CAL--0-0
Data is either a - or a 0
First 0 is wheel sensor, second 0 is infrared beam


Verifies alignment of the sensor and magnet and that the receiver sees the transmitter. To select, press and release MODE three times. P3 appears. Press START, and CAL ---- appears. Rotate the sensed wheel, and CAL--0-- appears as the magnet passes the sensor. As long as the 0 blinks on and off with each passing of the magnet, the sensor is seeing the magnet. Only a moving magnet will change a - to a 0 or a 0 to a -.


To verify the infrared beam, aim the transmitter at the receiver and CAL----0 appears. The 0 indicates that the receiver sees the transmitter. Press MODE to return to normal.


P4 Retrigger period.
Display format is P4----XX
Range is 1 to 59 seconds


This mode allows you to change the normal 5 second delay to a delay from 1 to 59 seconds. P5 sets this mode in the display. To select, press and release MODE four times. P4 appears. Press START, and ----- appears. Enter the number in the display, pressing START once to increment the number by one. Hold START down to rapidly increment the number. To select the number and return to normal, press MODE.


P5 Tire size factor.
Display format is P5-XXXXX
Range is 3328 (5 in. dia tire) to 21504 (30 in.)
Calculated from worksheet or program


This mode adapts the Performance Monitor to the tire and wheel size of your car. The size factor needs to be performed at the time of installation and whenever you change tire size. To select, press and release MODE five times. P5 appears. Press START, and ----- appears. Measure the tire diameter. It must be between 5 and 30 inches. Multiply it by 712, which results in a number betweeen 3328 and 21,504. (For example, a typical 20 in.-diameter tire has a factor of 14,240.) Enter the number in the display, pressing START once to increase the number by one, up to 10. After 10, hold START down to increment at 100/sec. When close to the number, increase one number at a time. To select the number and return to normal, press MODE.


P6 Performance Monitor bar graph sensitivity.
Display format is P6----XX
Range is 1, 2, 4, 8, or 16 wheel revolutions
8 segments faster and 8 segments slower


Allows you to vary the wheel revolutions per bar of the Performance Monitor display from 1 to 16. To select, press and release MODE six times. P6 appears. Now press START, and ------ appears. Enter the number in the display, pressing START to increment the number from 1 to 2 to 4 to 8 to 16 then back to 1. Hold START down to rapidly increment the number. Press MODE to select the number and return to normal.


To activate the Computer Interface. With the microcomputer off, hold down the MODE button and turn on the microcomputer. Display shows LoAd Pc. This alerts the system that a computer will be communicating through the serial port.


To clear the memory. With the microcomputer off, hold down both START and MODE buttons and turn on the microcomputer. The display indicates all dashes (--------) and memory clears and starts over.


Battery Indicator. A new 9V battery has 9.2V. If battery voltage is 8.7V Lo b shows on the display when the system is first turned on. The battery should be changed. If voltage is 6.7V dEAd b shows at turn-on and the system will not perform reliably.






Microcomputer: (21640) Mat'l: black plastic case. Size: 3-1/4" W x 5-1/2" H x 1-1/2" D overall. Weight: 9 oz. including 9V battery (not supplied).


Early Wheel Sensor:Hall effect. Size: 1-1/2"W x 3/4"H x 3/8"D overall. Weight: less than 1 oz. Two holes permit attachment with 6-32 screws. Mounting: screws, nuts, standoffs supplied.


Wheel Sensor: (Model 21630) Hall effect. Size: 1-1/4"W x 3/8"Diameter. Weight: less than 1 oz. Rubber cushioned metal loop clamp permit attachment with 1/4-20 screw.


Magnet: Neodymium Iron Boron magnet with MGO energy grade 3714. Size: 0.25" dia. x 0.10" thk. Weight: 0.022 oz. Mounting: glue to rim with epoxy.


Steering Wheel Switch: (21616-4). Telephone curly cord. Size: 3' coiled, 10' extended. RJ-8 4-conductor connector on one end, permanently attached switch on other end.


Cable Pair: (21637). Telephone-type cord. One 3' long, one 4' long. RJ-11 6-conductor connectors all ends.


Serial Port Connection: Female 9-pin D.


Data Acquisition Connection: Pin 9 of the serial port connector is open collector signal that goes high when receiver detects transmitter and stays high for length of time selected for retrigger delay. Ground is pin 5.





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