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Circuits > Games and entertainment > JAM(Just A Minute) Circuit
JAM(Just A Minute) Circuit
This jam circuit can be used in quiz contests wherein any par- ticipant who
presses his button (switch) before the other contestants, gets the first chance
to answer a question. The circuit given here permits up to eight contestants
with each one allotted a distinct number (1 to 8). The display will show the
number of the contestant pressing his button before the others. Simultaneously,
a buzzer will also sound. Both, the display as well as the buzzer have to be
reset manually using a common reset switch. Initially, when reset switch S9 is
momentarily pressed and released, all outputs of 74LS373 (IC1) transparent latch
go ‘high’ since all the input data lines are returned to Vcc via resistors R1
through R8. All eight outputs of IC1 are connected to inputs of priority encoder
74LS147 (IC2) as well as 8-input NAND gate 74LS30 (IC3). The output of IC3 thus
becomes logic 0 which, after inversion by NAND gate N2, is applied to
latch-enable pin 11 of IC1. With all input pins of IC2 being logic 1, its BCD
output is 0000, which is applied to 7-segment decoder/driver 74LS47 (IC6) after
inversion by hex inverter gates inside 74LS04 (IC5). Thus, on reset the display
shows 0. When any one of the push-to-on switches—S1 through S8—is pressed, the
corresponding output line of IC1 is latched at logic 0 level and the display
indicates the number associated with the specific switch. At the same time,
output pin 8 of IC3 becomes high, which causes outputs of both gates N1 and N2
to go to logic 0 state. Logic 0 output of gate N2 inhibits IC1, and thus
pressing of any other switch S1 through S8 has no effect. Thus, the contestant
who presses his switch first, jams the display to show only his number. In the
unlikely event of simultaneous pressing (within few nano-seconds difference) of
more than one switch, the higher priority number (switch no.) will be displayed.
Simultaneously, the logic 0 output of gate N1 drives the buzzer via pnp
transistor BC158 (T1). The buzzer as well the display can be reset (to show 0)
by momentary pressing of reset switch S9 so that next round may start. Lab Note:
The original circuit sent by the author has been modified as it did not jam the
display, and a higher number switch (higher priority), even when pressed later,
was able to change the displayed number.
Title: JAM(Just A Minute) Circuit
Source: www.electronic-circuits-diagrams.com
Published on: 2005-02-01
Reads: 955
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