An Accurate Reaction Timer


Add a cheap stopwatch to
this circuit to produce an accurate reaction timer. The circuit is
wired in parallel with the start/stop button in the watch via a 2.5mm
socket, which fits snugly in one corner of the casing. The person
conducting the test (the “tester”) resets the stopwatch and turns on the
reaction timer’s power switch (S3). The person being tested (the
“subject”) places his or her fingers near the “STOP” push-button switch (S4). Next, the tester covertly sets a delay time with VR1 and selects either the LED or buzzer alarm via S2. To initiate the sequence, the tester then presses the “START
switch (S1). This triggers 555 timer IC1, which is wired as a
monostable. Its output (pin 3) goes high for 2-12 seconds as determined
by the setting of VR1. At the end of this delay pin 3 goes low and
triggers IC2, another 555 timer in monostable mode.

An Accurate Reaction Timer Circuit

An Accurate Reaction Timer Circuit Diagram

The output from IC2 (pin 3) activates the alarm (buzzer or LED)
for about 0.5s. After inversion by Q1, it also triggers IC3, another
555 monostable. The positive pulse from IC3 turns on Q2, briefly closing
the start/stop switch circuit in the watch. The watch starts to count
up. After a short period, the subject reacts to the alarm and pushes the
STOP” button (S4), freezing the stopwatch.
The reaction time can then be read off with 1/100th of a second
accuracy. Comparative reaction times could be measured when a subject
is: rested or tired, silent or talking, before or after a night out,
using a mobile phone, etc. For motoring realism, rig up dummy
accelerator and brake pedals, with the brake switch making the stop
contact. Or take it to your club and test people as they enter and after
they’ve been “steadying their nerves” at the bar.

Author: A. J. Lowe – Copyright: Silicon Chip Electronics


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