Programmable_100_hour_timer_with_display

Published:2009/7/21 23:00:00 Author:Jessie | From:SeekIC

Programmable 100-hour timer with display. The 8260 on the right uses the carryout gate to generate a t -second clock from the 60-hertz line. The diodes on the time base input rectify the input signal and alternately clamp and release the internal pull-up resistor at pin 14. The input network depends on the amplitude of the 60-hertz signal available. The internal oscillators are disabled with a t K resistor at pin 13. The second and third 8260s are programmable with thumbwheel switches up to 59 seconds and 59 minutes. The carryout of each divider drives the next counter. The 8250 was chosen to give the maximum count of 99 hours. All request pins are tied together and back to the 10K output pull-up resistors at the thumbwheels. The timing cycle begins by pressing the pushbutton. The 7045 provides a counter chip pulse direct drive to the 7-segment LEDs. Timing resolution can be increased to hundredths of a second by substituting 8250s for the initial stages and using the 60-hertz line to generate a 100-hertz clock (courtesy Intersil, Inc.).



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