For full size cars the detection zone is much bigger as the tracks are wider, its actually easier to detect a faster full size can than it is a fast RC Car on a narrow track. The transponder signal is the 100Hz signal, this means that in a car travelling at 60Km/h we should receive six pulses in the time it takes the car to travel one meter, this is enough for use to reliably detect an RC Car. The second circuit is much slower and simply switches the first circuit on and off at 100Hz (100 times a second). There are also many online calculators giving required component values for the frequencies you enter -įor our transponder we want two on/off circuits running at different frequencies, the first is a 38Khz circuit which switches the Infra Red LED on and off 38,000 times a second. Here is a nice introduction to the 555 Timer. The type of circuit we want to build is called an 'astable' this is a circuit which has two states (on and off) but is not stable in either of them, the circuit continually alternates between the two states - on,off,on,off and so on. The 555 timers use a simple set of external components to set the timing behaviour and frequency. The timing circuit is based on two 555 timers, these are the basis of many introductory electronics projects so are widely available and inexpensive. If you want to read the code, you can open it with the Arduino IDE. The arduino (the software) clocks each laps and in the end prints out the times. ![]() So when the infrared beam is broken, the clock starts ticking. The diode is include to protect the rest of the circuit from accidental reverse power connection. The lap timer works based on a 'flying start'. You can replace the 7805 regulator with more modern alternatives, just ensure to use the supporting components recommended in your chosen regulators datasheet. We use the 5 volt output to drive the timing components which actually produce the transponder signal. ![]() I have used a 7805 regulator, this takes the 8.4-7.2 volts supplied by the car battery as input and produces a steady 5volts as output. The solution used in this final design is to add a voltage regulator which prevents noise crossing from the car into the transponder or equally important -from the transponder back into the car. In most of my cars the earlier versions of the transponder were perfectly reliable however I just couldn't get the earlier designs to work in this particular car, after 20 laps or so the laptimer could not longer detect the signal. The final version of the transponder has been tested in an RC Race car running an electrically noisey brushed motor and a noisey electronic speed controller.
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