Digital Reaction Timer
It is an ideal project for those who want to build something that not only teaches them something but also gives them lot of fun. As the title suggests, this gadget can be used to measure quantitatively the reaction time of an individual. The reaction time can be measured in two different settings: In the first setting, the reactiontime can be measured upto a maximum of 99ms with a resolution of 1ms. In the second setting, the reaction time can be measured upto a maximum of 990ms with a resolution of toms. You can try this gadget with your friends and relatives and find out how quickly they react to a given situation.You can, try this with yourself too at different times and when you are In different states of mind and see the difference yourself.
The circuit is basically a counter clocked by a clock generator having two different frequency selections of 100Hz and 1000Hz. There are two push buttons represented by micro switches SW1 and SW2. One of the push buttons to be held by the examiner is used to start the counter and the other push button to be held by the examinee is used to stop the counter. The display reading obviously gives the time interval between the start and stop operations and hence the reaction time. The display reads the reaction time in milliseconds directly if the clock is set at 1ms period and it reads one tenth of the reaction time in milliseconds if the clock is set at toms period. The functioning of counter type 4510 has been explained in detail in the project DIGIKIT-III. The present circuit is nothing but a cascaded arrangement of two such counters thus extending the capability of the counter up to a maximum count of 99.clock pulses are continuously applied to the counters’ clock inputs. The RESET points of the counters are fed from the output of a J-K flip flop wired as a T-flip flop. Initially, the flip flop is kept in the HIGH output state so that the counter is reset to 00. Also, in this condition, LED-2 is OFF. The flip flop is made to toggle when the examiner presses the push button thus sending a pulse to the clock input of the flip flop. This removes the RESET condition from the counter and it starts counting. The flip flop is again made I to toggle and thus reset the counter by the examinee when he or she presses the push button provided to him or her. It may be mentioned here that the person under test has to press his push button (only in response to the lighting of LED-2. LED-2 lights when the person who is the judge presses his hush button.
The clock generator is a simple circuit built around three NAND gates in cascade The frequency of this clock generator is given by f=0.56/RC
where R = R5 = R6 and C = C1 or C2
Reslstors and capacitors
R1 to R4 : 22K 1/4W
R5, R6 : 560K, 1/4W
R7 to R20 : 680 ohms, 1/4W
R21, R22 : 3.9K, 1/4W
C1 : 0.1µF (Polyester)
C2 : 0.01µF (Polyester)
Semiconductors and ICs
LED-2 and LED-2 : Miniature LED
IC-1 : CD 4011
IC-2 : CD 4071
IC-3 : CD 4027
IC-4 : CD 4011
IC-5, IC-6 : CD 4510
IC-7, IC-8 : CD. 4511
IC-9, lC-10 : LT 543 (Common cathode type seven segment display)
SWI, SW2 : Microswitches
SW3 : SPDT
SW4 : Miniature toggle switch
9V battery, solder metal, wires, IC bases
Figs. 19.2 and 19.3 respectively show the PCB layout and components layout.
The test gadget can detested asper the following procedure:
1. Initially, keep the switch SW3 in position-1 so as to select 100Hz clock frequency. Check that the LED-2 is OFF. lf it is not so, pressing release SW1 once.
2. Once the LED-; is OFF, this ensures that the counter is in RESET mode. Now you are ready to check the reaction time.Hold the microswitch SW1 in your hand and ask the other person (whose reaction time is to be determined) to hold the switch SW2 Instruct the other person to concentrate on the LED-: and press the switch SW2 immediately when he sees the LED-: glowing.
Now, press the switch SWl without telling the other person. The reading on the display gives his reaction time in tense of milliseconds.
That is, the actual reaction time is 10 x display reading.
5. lf the person is too quick and the reaction time comes out to be less than or equal to 99ms, you can repeat the test by changing over the clock frequency to 1000Hz. This will give you a more accurate value.