Electronic Reflex Tester
This project was included so you can compare your reflex time with someone else's. The circuit is an adaptation of the push-button relay control circuit of project Code Practice Oscillator with Tone Control in Communication systems section.
The game takes two people and is played as follows:
1. Have one person place their finger on the slide Switch and prepare to push it down (OFF) at the signal.
2. Have a second person place their finger on the Key and prepare to push it down (ON) at the signal.
3. First open and then connect the wire lead to the emitter of the 2SA Transistor. This accomplishes two things: places the Lamp ON, and completes the circuit so the game can be played.
4. Give the signal to press the Key. If the Lamp stays ON, the person controlling the slide Switch has won. If the Lamp goes out, the person pressing the Key has won. There is no such thing as a tie in this game.
Additional keys may be placed in parallel with the Key supplied, and additional normally closed switches added in series with the switch in order to have teams. This type of circuitry has been used with quiz teams where the side to "jump" first gets to try to answer a question.
The circuit used is the electronic version of a push-button relay control circuit. The Key-Switch circuit must be completed to obtain Transistor base-bias to actuate the Relay. Once the Relay is energized, the closed contacts completes the Transistor base-bias circuit so the Key-Switch circuit has no more control.
The Relay is de-energized by opening the field coil circuit at the Transistor emitter. Obviously if the Switch is opened before the Key is pressed the circuit cannot be completed and the Relay remains de-energized.
The silicon (Si) Diode across the Relay keeps the turn-OFF surge of energy from the Relay from damaging the Transistor (by circulating the current from this surge back into the Relay). It is not required in this circuit but is included as a reminder that all high-reliability circuits must include some means for handling such potentially destructive surges.