The frequency can be adjusted within a Wide range of values using a potentiometer. The circuit operates as follows.
ICl-a is a free-running, low-frequency oscillator operating in a frequency range between 0.1 and 1 Hz. Oscillator output pulses are applied simultaneously to the IC1-d input and to an RC network formed by R3, R4, and C2. The time constant of the network will delay the output pulse to be applied to pin 14 of IC 1-d.
Thus, according this delay, the output pulse of IC 1-d and the duration of the lamp flash will be altered.
If we have small delay, the two ICl-d input pulses arrive at practically the same time, and the duty cycle of the lamp flash will be the same as the free-running oscillator formed by IC 1-about 50 percent.
But, by adjusting R3, we can trigger IC1-d with large delays. If the delay is long enough to trigger IC1-d at the end of the pulse, we will get low-duration flashes or small duty cycles.
D1 is used to discharge capacitor C2 at the end of each pulse. When IC 1-a output goes low, between flashes, D1 is directly biased, causing C1 to discharge through it.
A Darlington power transistor is used in the output stage to drive lamps up to 1 A.
The lamp can be replaced by high-power white LEDs wiring a series resistor in series to limit the current. The resistor can range from 22 ohm to 220 ohm according the LED.
The power supply can be a 6 or 12 V unit, depending on the lamp or LED.
The device can be used as part of warning systems, alarms, decorations, and so forth. C1 and C2 can be altered to change the frequency and duty cycle, but the values should be close as possible.
A schematic diagram of the device is shown in Fig. 1.
Transistor Q1 must be mounted on a heatsink. The lamp can be the same one suggested in other projects using the 4093 in this site. A suitable base for the lamp should be used.
The transistor can be replaced by a power FET to get better performance. Any “IRF” power FET with drain currents rated at 2 A or more can be used in this project.
You can replace the lamp with a 6 or 12 V relay to control external loads, including common 117 Vac lamps.
IC1 - 4093 CMOS integrated circuit
Q1 - TIP120 Darlington power transistor
D1 - 1N4148 general purpose silicon diode
L1 - 100 mA to 1 A, 6 V or 12 V lamp (see text)
R1, R3 - 2,200,000 ohm potentiometer
R2, R4 - 100,000 ohm, 1/4 W, 5% resistors
R5 - 4,700 ohm, 1/4 W, 5% resistor
C1, C2 - 0.47 or 1 µF ceramic or metal film capacitor
C3 - 100 µF, 16 WVDC electrolytic capacitor
