This circuit is a useful timer with many applications. It features two modes of operation: "50/50 duty cycle" and "1-shot". The timer is adjustable from a few seconds to a maximum of about 12 hours.

It has a unique feature by which you can adjust long periods by simply adjusting it in the minute mode and then changing the switch to hour mode so you won't have to wait for a long time for measuring the time period. When the timer is changed from minute mode to hour mode, the time duration will be approximately 64 times the time duration measured in minute mode.

In the cyclic mode, the same length of period will be repeated on the 50 / 50 basis duty cycle.

In addition to its continous pre-set adjustment, it has 5 fixed timing periods which can be selected by the position of the jumper. The timing periods are shown on the table below.

Jumper Position	Minute Mode	Hour Mode
T1	1 Min	64 Min
T2	1 Min 55 Sec	2 Hr 2 Min
T3	2 Min 52 Sec	3 Hr 3 Min
T4	3 Min 50 Sec	4 Hr 5 Min
T5	5 Min 16 Sec	5 Hr 37 Min