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555 digital timer circuit used in competition

2015-02-03 10:33  
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555 digital timer circuit used in competition
As shown in the figure 11-33, the timing circuit still uses inexpensive 838 calculator as display terminal, it is composed of second clock generator and photocoupler. It can be used in counting second occasions such as sports tournament, intelligence competition, the reading is accurate and visualized, it also has suspensive function. The actable multivibrator is made of IC(555) and R1, RP1, C1, the oscillation frequency is f=1.443/(R1+RP1)C1, the frequency can be adjusted to 1Hz by RP1. K1, K2 are closed, then IC starts to vibrate. The 3 foot output is added to photocoupler, the isolated output is added to = key of 838 calculator. Before timing, it should operate calculator firstly, it is counted for accumulating 1, in other words, pressing ON/C key → + key → 1 key, then K1, K2 are turned on.