long period timer

• r long-pertod time This monostable multivibrator can be seen as a long-period alternative for timer circuits which incorporate the well-known 555. It allows the user to obtain on-off periods varying from 20 seconds to about 60 hours. The design is quite simple. It consists of a start/reset part, a "slow" oscillator and a series of flipflops. Most of this can be found, ready for use, in IC1. For only a further two 2.5 and 25 seconds by rotating P1. Depending on K is connected to which one of points A, B, C point X, a logic "1" will be sent to the clear input via R5 after a short or very long (pin 4) of FF1 period. This way, the flipflop is cleared, the Q output becomes "1", and the oscillator stops. The "timer" will start up again only after a new start pulse reaches pin 3 of FF1. Due to the very large number of possibilities, there is a formidable choice of periods to chose from. When points A and X are connected, the time set with P1 can be varied to range from 20 sec. to 3.5...