Circuit diagram:
Parts:
R1_____________10K 1/4W Resistor R2____________220K 1/4W Resistor R3____________500K 1/2W Trimmer, Cermet or Carbon R4______________1K8 1/4W Resistor (See Note) R5______________1K8 1/4W Resistor C1_____________47µF 25V Electrolytic Capacitor C2______________1µF 25V Electrolytic Capacitor C3_____________10nF 63V Polyester Capacitor D1___________1N4148 75V 150mA Diode IC1____________4060 14 stage ripple counter and oscillator IC Q1____________BC327 45V 800mA PNP Transistor (See Note) SW1____________SPST Brake Switch B1______________12V Vehicle Battery
Comments:
Circuits of this kind are intended to drive LED Arrays in order to create more visibility and conspicuity when a vehicle is stopped or stopping. This circuit, in particular, will emit a visual alerting signal of 4 short flashes, followed by a steady on light that remains steady on as long as the brakes are applied.
Circuit operation:
IC1 internal oscillator generates a square wave whose frequency is divided 64 times by the flip-flops contained in the chip in order to obtain about 1 to 4Hz at pin #4: this is the LED Array flashing frequency and can be set to the desired value by means of R3. A positive signal at D1 Cathode stops the oscillator after 5 pulses are counted. C2 and R1 automatically reset the IC whenever the brakes are applied. Q1 is the LED Array driver: LEDs will be on when pin #4 of IC1 goes low.
Note:
- The transistor type suggested for Q1 will drive LED Arrays at currents up to 500mA. To drive Arrays requiring higher currents (up to 1A and even more) use a BD436 (32V 4A PNP Transistor) for Q1 and a 1K resistor for R4.
