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MITTENTITEL |
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Scalextric hand controller or is it the black knight ?
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Powerbase Inside the 4 car powerbase we find a Microchip 16F819 processor. It's in the same league as the processors used by the other manufactureres. A Desgin pecularity is the power stage formed by a full H bridge instead of the usual half H bridges. This is due to the fact that AC is used on the tracks. The fets are rated with 8 A at 100°C. The output driver stage has a very high resistance (which is bad) of 1.8Ω. When entering powerbase the voltage is immediately reduced by thre diodes. The only explanation I have is that the external power supplies had already been ordeerd when a problem showed while using 15V. And instead of switching to a different power supply, they used diodes to "correct" the voltage. But that's pure speculation. Power supply A stabilized switching power supply rated 15V and 4A. Hand controller Those are special in two ways. For one they have two buttons, one for lane changeing and one for brakeing. And the second pecularity is that the throttle and the two buttons are all daisy chained using a rather analog method in a rather digital system. The chain is made by three resistors. A 5 kΩ potentiometer used as throttle, a 18 kΩ resistor for the brake and a 8.2 kΩ resistor for the lane change. The two buttons are break connect buttons and each one is placed, so that it will short circuit one of the resistors when not pressed. So with no button pressed the resistance between the contacts of the jack will be between 0 and 5 kΩ depending on the throttle setting. When the lane change button is pressed 8.2 kΩ are added to the resistance. When the brake button is pressed 18 kΩ are added to the throttle resistance and when both buttons are pressed 26.2 kΩ are added. The controllers use 2,5mm mono-headphone jacks. |
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Out of harms way. |
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Cars The cars use IR leds to send id and state of the lane change button to lane changer, lap counter and other add ons. The cars send this signal all the time. The frequency is based on a 48µs and this results starting with car id 1 in frequencies of 5208, 4167, 3472, 2976, 2604, 2314 Hz etc.. The duty cycle is 3 : 1 and changes to 1 : 3 when the lane change button is pressed. The car decoders are very small, despite the need to fit a bridge rectifier in. Main reason is the use of small fets in the power stage. The small fets are rated 1,7A in the driver loop and 0.9A in the brake loop. The usual caution towards such values applies, because a thermal overload can happen even when the current limit is not reached. The PWM frequency is 290 Hz, occasionly 319 Hz. The frequency change seems to be erratic and looks more like a fault than a feature. The PWM frequency is rather low, and there is a big capacity at the motor, which might be due to the low PWM frequency. The decoders available to me, did not have any support for lights. |
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Modern solution for an old hashioned problem: |
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Lane changer The lane changer electronics analyzes the IR signal and switches the lane changer accordingly. The tongue stays in its position until a later car changes it. Same principle as with D143 or the other way round. The curved lane changers have seperate sensors and are build symetrically. In theory you can move the electronics from one end of the lane changer track to the other end and connect the sensor track to the other end and convert an inner right curve lane change to an outer left curve lane changer. That's not important per se, because you can buy lane changers in all variants, but it shows that some engineer has put thought into what he did, and that's always nice to see. Pit stop lane The pit stop lane I had was just a single track lane changer. But there is also a pit stop game, which has some additional electronics. Both work completely independent from the powerbase. Lap counter That's nearly all there is to tell. It counts laps. No times, only the number of the leading car is displayed while a race is on. That's it. It does work autonomous from the rest of the track. It uses IR sensors to read the id of passing cars and does it's thing. No further interaction with cars or powerbase. No jump the gun detection, but if a car crosses the starting line ahead of the race it's first lap will not be counted that should be penalty enough. This sounds not like much, but it is just enough to have fun with the crowd and the big, friendly and bright numbers make it very easy to read. The end Less is more, min to the max. That seems to be the slogan of Scalextric digital. The number of features supported by the powerbase is very close to zero. On the other hand, this system has the best car control of all due to it's 64 speed levels and 52 Hz data rate. And this is fun in itself. |
