Standard scooter flasher units have two major drawbacks. First of all, they need a high enough operating current to make them switch. Hence it’s impossible to operate in ‘LED’ mode (at less than 5 W). Secondly, they offer little or no audible warning if you forget to turn the indicator off. As scooter indicators aren’t self-canceling, many riders forget to turn them off.
The simple solution with two diodes and a sounder is effective, but quite a nuisance in town, as the beep-beep soon becomes irritating. So the aim of this project is to solve this problem. It works with loads of around 1–40 W.
D1 protects the circuit against reversed polarity. This diode can handle up to 6 A in a small package. Together, R1, T3, and IC1 form a current detector. IC1 is wired as a comparator and switches cleanly according to the current flowing in R1 and the setting of P1.
IC2.A and IC2.B are wired as a monostable. As soon as IC1 output goes high, R4 starts charging C3. IC2.B then goes high and T3 turns off. IC1 then switches over, IC2.B follows it a little later, and T3 turns on again. And so on… D2, D3, R5, R6, and T1 form the equivalent of a NOR gate driving the reset of the counter that follows. This means the counter can be reset even without turning off the ignition. The counter is reset as soon as both pins 1 and 4 of IC2 are low together.
The counter IC3 is a CD4060 wired so that its output Q6 goes high every 64 pulses on pin 11. As the network, R4/C3 times the switching at around a second, after around a minute IC3 output Q6 goes high and, via IC2.C, IC2.D, and T2, the sounder operates in time with the indicator. In the download for this article [1], you’ll find the author’s PCB design and a few photos of the project. The width of the board is based on the inside diameter of a 32 mm PVC tube, i.e. the standard diameter of normal flashers.
The length is determined by the board’s track requirements but is well below the size the majority of scooters can accommodate. Remember to heavily in the tracks carrying high currents. The MOSFET doesn’t need a heatsink. Fix the PCB inside the tube using hot-melt glue, taking care not to glue up the preset P1!
Internet Link
[1] www.elektor.com/100939
