Digital timer - programmable long time multivibrator

H The analogue brother of this IC is our old friend, the 555. The digital version here, the LS 7210, is less well-known. It can be used to set delay times between approximately 11 ps and 42 minutes. The IC contains an oscillator of which the frequency determining elements are connected externally (R1 and C1). This then provides the frequencies as shown in table 1. The IC is programmed for internal oscillator operation by con- necting pin 4 to 0 V. The delay time T is derived from the formula: T = (1 + 1.023 • N)/f where "f" stands for frequency according to table 1, "N" is the multi- plication factor as determined by pins 8 .. . 12. These pins have the following values: pin 12 = 1, pin 11= 2, pin 10 = 4, pin 9 = 8 and pin 8 = 16. For example, if N is to be 25 then pins 8, 9 and 12 must be logic "0" (0 V). In this case, with the oscillator frequency set to 0.013 Hz, the total delay time will be 34 minutes. As shown in the circuit diagram, the IC is used as a retriggerable monofl...