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Download # 8 in PDF
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While the Timer-Alarm described on Circuit
No7 can be calibrated within seconds of the required time, the circuit
shown below is the basic timer circuit where the two resistors between
pins #4 and #5 R-120k and Variable R-20k are used to calibrate the time
delay. Frequency required for each time delay can be calculated for each
minute increments i.e... one minute = 140.08khz, while 5 minutes = 140.08khz
divided by 5 =28.16khz etc.. A frequency meter is connected at pin #5 of
the IC and RV-20k is rotated to obtain the Frequency/time relation and
noted by measuring RV-20k resistance or time marked on the enclosure when
circuit enclosed.
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sheet in PDF
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