MITTENTITEL

Lane changer:
A car without wheels, as far as the electronics are concerned.

Blackbox

the heart of Carrera's black box is an Atmel Mega 16 running at 8 MHz. That's all the computing power there is.

That's interesting news, because the Mega 16 has no built in USB functionality. And so it is not surprising that the PC-Unit connector is not USB compatible. Instead the connector is connected to the serial interface of the Mega 16. It's rather obvious that the PC-Unit will consist only of a serial-usb or a 5V-RS232C converter. It's a pity that you can't see from the outside what functionality will be offered by connecting the Blackbox to a PC. My studies about the lap counter hint strongly to the fact, that the only functionality offered by connecting computer and blackbox is updateing the firmware of different system components.

The Mega 16 is able to program itself, so an software upgrade is possible.

The Modul-Connector is connected to the SDA and SCL line of the Mega 16. This means that there is an I2C interface as well, but again there is no information available what the interface can be used for.

The power amplifier is designed as a pseudo half H-Bridge. The drivier fet is specified with 8A at 100°C. The transistor which will gurantee a low level, when the driver is switched off, is only able to source 200mA. But it is protected by a resistor, so it will not be overloaded even in case of a short circuit. The output driver stage has a low (which is good) resistance of 0.42Ω.

In addition to the "ordinary let the cars drive" services, the Blackbox offers the control of a "cars please use the fuel feature" bit, start lights, detection of early starters and pace car control.

Power supply

For D132, a switched and therfore regulated power supply specified with 14,8V and 3,5A, is used.

There is an adapter in the D124 conversion kit. It allows the use of a Carrera Exklusiv power supply with the blackbox. This is an unregulated power supply rated 18V, 1,2 A.

There is also a dedicated D124 digital powersupply. This is switched and regulated and rated with 18V, 3A.

Cars

The cars send their id continiously using an IR Led. Each id has a fixed frequency. The cars with ascending ids use the following frequencies 15,625 kHz, 7,8125 kHz, 5,208 kHz etc. Thats a pulse duration of id (starting with 0) * 64µs. Ghostcars identify themselves with id 6 (controller number 7), and pacecars with id 7.

The pulse ratio is 1:1.

15,625kHz is also the frequency of the motor PWM. 16 different throttle settings incl. stand still result in a shortest puls of 4,27 µs.

The power amplifier is a half H-Bridge. The fets are rated 8A at 100°C.

The decoders support front and combined rear and brake lights. The main lights can be switched on and off for each car seperately from the respective controller.

Lane change

The lane change electronics monitors the data on the track and saves the state of the lane change switch for each car.

When the electronics recoginize a car by receiving it's id through IR transistor, they will check the stored state of the lane change switch for that car and act accordingly.

The use of a pulsed signal to activate the lane change ensures that random light changes will not trigger the lane change as it could happen with the Pro X system.

There is only one solenoid to move the flipper, it is returned to it's default position by the slot guide pressing against a lever..

Pit stop lane

The pit stop lane consists of a lane change and a pit stop track which is electrically seperated from the main track. Because of this seperate loop, you must use the pit stop lane entry and exit track to connect the pit stop lane track to the main track. If you replace either or both with ordinary lane changers the pit stop feature will not work.

On the separate loop of the pit stop lane the same information as on the main track is transmitetd, but at the end of every data word the pit stop lane electronics append a low phase. This additional low phase signals to the cars that they are inside the pit stop lane. What they do with this information is up to them.

The pit stop lane has nothing more to do with the "fuel feature", all it does is telling the cars when they are in the pit stop lane.

Refueling

The cars handle all the fuel matters themselves. The blackbox uses a bit in the data stream to tell the cars whether to use the fuel feature. Usualiy the setting of the fuel switch is send to the cars. But when a race is started by pressing the start button on the blackbox, all data send to the cars will have the throttle set to zero and the fuel feature bit set to off. This automatically refuels the car. After the start sequence is over, the setting of the fuel switch will be sent to the cars.

That is all the part the blackbox takes in fuel managment. And that is the reason why there is no way to display the fuel level of any car, with the standard fuel management.

When the fuel featuere bit is cleared the cars will be immediately refuled and so they will never run out of fuel as long as the bit is cleared.

When the fuel featuere bit is set the cars will decrement the fuel count. The higher the throttle setting the more will be deducted. When the fuel level reaches a threshhold the lights will start to blink and when the count reaches zero the car will stutter.

When a car enters the pit stop lane it will recognize the additional low phase at the end of the data words. If now the throttle setting also falls to zero the car starts to refuel itself by increasing its fuel count. As long as the fuel level has not reached the top the lights on the car will blink.

Lap counter

The lap counter gets a start signal over a separate cable from the blackbox. It's one of those design decisions that leave me speechless.

The lap counter handles all other task on it's own.

There are two IR sensors per lane. One in the top of the track which reads the id from the IR transmitters of passing D132 cars and another sensor in the slot which reads the ids coded in special Pro X guiding blades. While in theory the top sensor would be enough to measure the times for digital cars, Carrera will use both sensors. The id is read by the top sensor, but the time is triggered by the sensor in the slot. This ensures that the times measured for ProX and D132 cars use the same point for triggering time measurements.

The end

It's quite interesting to see how many tasks the cars have to handle on their own. Lights managment, ghost- and pacecar modes, fuel management are all handled without assistance of the blackbox. All the blackbox does ist transmitting button presses and throttle pushes and leaves it to the cars what to do with them.

The same is true for lap times and lap counts. But those are handled by the lap counter. A philosophy very different from SCX's, which has a blackbox stting in the center and pulling threads like a spider in a net.