When we are driving sometimes we do not know the speed of our car, especially when we are in the course of the highway so nice and straight, if the car's speed is too fast or faster than anyone could lead to accidents that do not want to happen. The circuit then requires the Car Speed Alarm is to alert the driver who did not notice the speed because the roads are nice and straight. Even this series can be set speed, for example, we set when exceeded 100km/h the alarm should sound.
The workings of the circuit:A piezo buzzer will sound. Speed pulse is inserted into the base of Q1 and the resulting waveform at the collector is fed through a RC network to the input of an LM2917 frequency to voltage converter, IC1. The resulting voltage is fed to three comparators (IC2d-IC2b) which has a reference voltage at the inverting input they are set by the 10-turn trimpots VR1, VR2 and VR3. The output of each comparator is applied through another RC network to the gate of an SCR. Anode of the three SCRs are commoned comparator inverting input connected to the left, IC2a.Non-inverting input is set to 2.3 V with a trimpot VR4. In use, once you exceed the speed setting for the comparator in particular, relating SCR to briefly pull the pin 2 of IC2a low and short beep is emitted by a piezo buzzer. Then, if you exceed the speed setting that followed, another beep will be heard. The idea is to make each setting speed of several km / h higher than it actually is, so if you are driving at the correct speed in a particular zone, the buzzer will not sound. But as you increase speed, the buzzer will beep once because you exceed the speed settings for each zone. In this way, there is no need to constantly switch setting the pace as you pass through different zones and you can choose to ignore the beep is not "illegal".