This assembly, besides a brake light can also serve as a mini vibration alarm or balance as an experimental seismograph for demonstrations in science fairs.
The operating principle is simple: installed in a box and taken on the bike with the light on the back it has a pendulum sensor (X1).
Under normal conditions the pendulum does not touch the ring (both must be made with bare wire). When braking occurs, the pendulum swings and touches the ring, causing the capacitor C1 to charge and throw for a few seconds X2 indicator lamp.
Of course the ring and the pendulum must be hard not to cause the circuit triggering the normal balance of the vehicle in which it is installed or when it passes in a hole or wave. Its mounting position towards the drive only occurring when braking is important.
The device is powered by batteries and instead of common bulb an LED can be used. A "jumbo" red LED in series with a resistor 100-33 Ω is recommended.
In Figure 1 we have the complete diagram of the device.
In figure 2 we have the arrangement of components in a small printed circuit board but it is possible to make a "hung" on a bridge assembly or common terminals strip.
The lamp must be 50 mA max both to avoid problems for the batteries and not force the transistor.
The delay is given by capacitor C1 which can have values between 47 µF to 470 µF.
The sensor is made of thick bare copper wire and the weight on the tip can be a ball made of epoxy dough.
To test the device is simple: just feed the circuit and jiggle the sensor so that the ring touch the wire with the weight. The lamp should light up and stay lit for a moment.
Proven operation is simply to a definitive installation on the robot or other application.
Q1 - BC548 and BC337 - General purpose NPN transistor
Resistors (1 / 8W, 5%)
R1 - 10 k Ω - brown, black, orange
R2 - 1 k Ω - brown, black, red
C1 - 47-470 µF / 6 V - Electrolytic
X1 - sensor - see text
X2 - 6 V x 50 mA - standard bulb
S1 - Single switch
B1 - 6 V - 4 small batteries
Terminal strip, support for 4 batteries, box mount, wire, weld, etc.