Schematic diagram for Seconds light flashes is based on an operational amplifier IC1 (LF351), which via the resistor R1 (100 ohm), R2 (100 ohms) and R3 (100 k) acts as a trigger Schmitt.
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At the output (pin 6) is a low voltage level, if the potential of the inverting input exceeds 2/3 V +. When reducing the voltage at the inverting input is below 1/3 V + of the operational amplifier output will go to a high level.
When connecting the inverting input to the RC-circuit (the condenser C2 (10 uF) and the variable resistor R4) It occurs periodic charging and discharging process, thereby causing vibrations undamped frequency 1 Hz.
Since the variable resistor R4 flashing frequency can be set accurately by the clock or approximate.
IC1 output is connected to the LED D1 (TIL209) through a coupling capacitor C3 (10 uF) and current limiting resistor R5 (470 ohms).
In the LED comes short current pulses during charging of the capacitor C3. The discharge of the capacitor occurs through the protective diode D2 (1N4001) to protect the LED from reverse voltage.
The current consumption of the device is about 2 mA.