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THE 556


THE 556
The 556 is a DUAL 555. It contains two identical 555 timer circuits. The NE556/SE556 timers can be directly replaced by the CMOS types MC3456/MC3556.

The following three pin-outs identify the 556 dual timer IC and the function of each pin.

Discharge is "in-phase" with the Output. (both are low at the same time)
Threshold
detects the high voltage on the capacitor and makes Discharge and Output go LOW
Trigger detect the low voltage on the capacitor and makes Discharge and Output go HIGH


Output HIGH (mS)

Output LOW (mS)


Frequency (kHz)


Calculate the Frequency, HIGH-interval and LOW-interval

for a 555 in ASTABLE mode. See answer below for Monostable (Delay):

Delay Sec


HIGH Interval (T1) = 0.693 x (R1+R2) x C

LOW Interval (T2) = 0.693 x R2 x C
Frequency = 1.44 / ( (R1+R2+R2) x C)