Introduction: 2 Player (or More) TTL Jeopardy Circuit

This is a 2 player "jeopardy" circuit made of extremely common and easily salvaged parts and can be expanded for more players. Component values/types are not too critical.

In this circuit, all transistors are acting as switches. The bipolar transistors are all (in this case) 3904's, but they can be just about any BJT suitable for switching. If the circuit were to be used with only LED buttons, this circuit could be simplified significantly, but this one was designed to switch large loads for each player so that brighter external lights can be controlled with the circuit. Q1,Q5 and Q3,Q2 comprise the flipflops that latch the players momentary button presses into continuous signals. These signals then enter Q9 and Q7 (part of the NAND gates Q8,Q9 and Q7,Q10) that lock out the other player. Q11,Q6 invert the signals from the NAND gates which drive Q12,Q13 ~ switches controlling the LED lights in the player buttons, Q6,Q11 which are voltage buffers for the mosfets and M1,M2 mosfets that control the external load. Q4,Q14 are switches that isolate the reset leads (bases of Q1,Q3) of the individual latches and allow a single wire to reset both, and this could likely be eliminated with a simple switch that connects the base of Q1,Q3 to ground. I'm no expert. D1,D2 are kickback diodes to protect the MOSFETs in the event inductive loads are used with the external lighting option. C1 is to act as a storage capacitor ~ in practice it was found that, while drunk, people hammer on the buttons. The batteries in their spring-held holders momentarily disconnect and cause the circuit to reset and allow input from the losing player to steal the win. Also, circuitry to ensure a reset-state upon startup was not included, so it is possible (and quite frequent) that one light will be lit upon turning on and require a reset signal before play. Therefore, a large storage capacitor (or a fancy super cap) is a must if rough use is expected.

To expand this circuit to more players, more flipflops are needed and each NAND gate gets longer. For example, for 4 players rather than 2, there would be 4 pairs of flipflop BJT's, 4 reset BJT's, and 4 NAND gates made of 4 BJT's each rather than the 2 NAND gates made of 2 BJT's each. Should be fairly simple but uses way more BJT's.

73! KE0KOY


14 - 2N3904 Bipolar Transistors

9 - 1k resistors

12 - 10k resistors

2 - 220ohm resistors

1 - 2200uF capacitor

2 - 2N4001 diodes

2 - IRF520 mosfets