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This game plays the Twinkle

Twinkle Little Star tune, or

another melody of your choice,

for as long as the player can

press the button corresponding

to the currently lit light-emitting

diodes (LEDs). The LEDs turn

on one at a time in a random

order and change at a frequency

of just over 1Hz.

Alternatively, you can

arrange the sequence so that the

Call the tune with this novel audio/visual

reaction timer

tune will play if the incorrect

buttons are pressed.

CIRCUIT DESCRIPTION

The full circuit diagram for

the

Twinkle Twinkle Reaction

Game

is shown in Fig.1. IC1 is

a 555 timer set up as a low

frequency astable multivibrator.

This controls the speed at which

the LEDs change their “random”

stationary position.

Another 555 timer, IC2, is

set up as a high frequency

astable. It is gated by the output

of IC1, with IC1's output

controlling the Reset line (pin 4)

of IC2. However, in order to do

this, IC1's output must be

inverted first, hence transistor

TR1 is used, set up as an

inverter. This is because the

Reset line on a 555 timer is

active low.

The output from IC2 at pin 3

feeds the Clock input of IC3 (pin

14), a 4017 divider/decoder.

This chip has ten outputs,

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Fig.1. Complete circuit diagram for the Twinkle Twinkle Reaction Game.

Transistor TR3 and resistors R12 and R13 are optional

−

see text.

Maxfield & Montrose Interactive Inc

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one of which switches on for

each successive clock pulse

with only one output on at a

time. However, in this circuit,

only the first six outputs (Q0

to Q5) are used. Each of the

used outputs has an LED

connected to it. These form

the display.

Also connected to the six

outputs are six pushbutton

switches, S1 to S6. The

outputs of these switches

feed a resistor/capacitor

circuit, R9, R10 and C4. The

best way to describe how this

works is to use the analogy of

trying to fill a bucket with a

small hole in it. If you turn the

tap on, you will fill it. Turn the

tap off and eventually the

bucket will empty.

The quantity here is the

voltage across capacitor, C4.

When the correct button is

pressed, the capacitor is

quickly charged. If the wrong

buttons are pressed continu-

ously, or no buttons are

pressed, the capacitor will

eventually discharge. The voltage

across this capacitor, when it is

above a preset level, switches on

the following circuit and thus allows

the tune to be played.

OUTPUT DRIVER

Transistor TR5 is used as a

driver transistor, and powers the

special tune generator IC4 with a

controlled voltage of 2⋅7V. This is

necessary as the tune generator

chip only works at voltages

between 2⋅5V and 3V.

This preset level is determined

by the Zener diode D15 and the

base-emitter voltage of transistor

TR2. The Zener's voltage is 2⋅7V

and the base-

Tune

Type (IC4)

emitter's

voltage is 0⋅6V.

Twinkle Twinkle Little Star

M66T-02B

Thus, the

Old McDonald Had a Farm

M66T-36

preset voltage

I'd Like to Teach the World to Sing

M66T-205

level across

White Christmas

M66T-214

capacitor C4

M66T-215

must be greater Warning Tone

than 3⋅3Vin

Table 1. Choice of Melody.

order to

switch on TR2. This

The voltage across capacitor

transistor acts as an inverter, as do

C4 also connects, via resistor R8

transistors TR3 (when used) and

and steering diode D14, to the

TR4.

Control Voltage pin (5) of IC2 and

When TR4 is

off,

its collector

provides a random voltage

element which changes the

actually be about 6V, while the

frequency of that astable. This

voltage across the second Zener

makes the light sequence of the

diode, D16, will be 3⋅3 volts. When

LEDs truly random.

TR4 is

on,

this short-circuits the

Zener, making its voltage 0V.

PLAY TIME

Transistor TR3 and resistors

R12 and R13 form an inverter,

which inverts the output function

from playing the tune when the

correct sequence of buttons is

pressed to playing the tune when

an incorrect sequence is pressed

(or no buttons are pressed).

These components are therefore

optional for this purpose.

The dashed link in the circuit

diagram is made as a fine copper

track on the printed circuit board

(PCB), therefore, if the inverting

function is required, this link must

be removed, by cutting the track

with a knife. This means that if

the normal function is required,

simply leave out TR3, R12 and

R13. If the inverting function is

required, break the track link, and

fit TR3, R12 and R13.

Maxfield & Montrose Interactive Inc

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COMPONENTS

Resistors

R1 390k

R2 to R6, R10, *R12, R14

10k (8 off)

R7 to R9, R11, *R13, R15, R16

2k7 (7 off)

All 0.25W 5% carbon film

*Optional - see text

POWER

CONSUMPTION

Current drain from a PP3

battery is under 20mA. A cheap

PP3 battery will thus give

approximately 6 to 10 hours of

continuous operation of the unit.

In casual use,

Twinkle Twinkle

can be used for several weeks

before a battery change is

required.

flattened side as shown in Fig.2.

The LEDs should be mounted to

the same height as the tops of

the push switches so that they

will all protrude from the case

by the same amount, which will

be about 2mm to 3mm.

Finally, solder the

transistors and IC4 straight onto

the board, as close as possible

to being flush with the PCB.

Construction is completed with

the insertion of the three ICs in

their sockets, observing correct

orientation.

Capacitors

C1, C3 4u7 sub-miniature radial

electrolytic, 10V (2 off)

C2 82p ceramic

C4 47u sub-miniature radial

electrolytic, 10V

CONSTRUCTION

The

Twinkle Twinkle

game is

built on a small single-sided

printed circuit board PCB. The

topside component layout and

underside copper foil master

pattern are shown in Fig.2.This

board is available from the

EPE

Online store

(code 210) at

www.epemag.com

Begin construction by fitting

the resistors. Be careful with the

diodes as the 1N4148 and the

Zener types can be easily

confused. Read the writing on the

components with a magnifying

glass if necessary.

One or two capacitors may

need to be fitted on the underside

of the PCB if they are too big to

fit on the topside. Sub-miniature

capacitors will fit on the topside,

but older, larger types, particul-

arly for the 47µF capacitor may

not fit on the topside.

The key dimension to

look out for is the

height of the comp-

onent, in fact, for any

of the components,

which must be less

than the height of the

outer rim of the push-

button switches when

mounted on the PCB.

The specified

pushbutton switches

are polarized, so make

sure you put them into

the PCB with the

Semiconductors

D1 to D6 5mm red or green

LEDs (6 off)

D7 to D14 1N4148 signal diodes

(8 off)

D15 BZY88C2V7 2.7V Zener diode

D16 BZY88C3V3 3.3V Zener diode

TR1 to TR5 BC108

npn

transistors

(5 off) (TR3 is optional - see text)

IC1, IC2 LM555 timers (2 off)

IC3 4017B decade counter

IC4 M66T-02B CMOS melody

generator (see text)

BOX PREPARATION

The prototype was built into

an MB3 type ABS plastic box,

size 79mm x 62mm x 39mm. It

just so happens that if the

bottom-right of the PCB is

located in the bottom-right

corner of the case lid, with the

bottom edge of the PCB

touching the bottom edge of the

case lid, all the switches and

LEDs will be in the center of the

face of the box when drilled.

To make the drilling easy,

simply make two faithful

photocopies of the component

side of the PCB (this should be

done on a

good

photocopier!)

and cut them close to the board

border outlines. Taking one of

the copies mark through to the

other side of the paper the four

Miscellaneous

S1 to S6 s.p.s.t. PCB mounting

push switches (push to make)

with round red tops (6 off)

S7 s.p.s.t. sub-miniature slide

switch

LS1 8 ohm to 100 ohm miniature

loudspeaker.

Printed circuit board available

from the

EPE Online store

, code

7000210 (www.epemag.com);

plastic ABS box (MB3), size 118mm

x 98mm x 45mm; 9V battery (PP3)

with clips; multistrand connecting

wire; M3 40mm long bolts (4 off);

M3 nuts (12 off); M3 washers

(4 off); self-adhesive rubber feet

(4 off); solder, etc.

See also the

SHOP TALK Page!

Approx. Cost

Guidance Only

$40

Maxfield & Montrose Interactive Inc

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&RQVWUXFWLRQDO 3URMHFW

mounting holes, and tape this

(reverse

side)

to the box lid with

its bottom-right corner sitting in

the bottom-right corner of the

box lid, the intended final

position of the PCB, see

photographs. Drill these with a

3mm drill bit.

Having removed the tape

and paper from the lid, mark out

and drill a small matrix of holes

to allow the sound from the

loudspeaker to escape. Do this

in the middle of the four PCB

mounting holes, to match the

size of your loudspeaker.

With the other photocopy,

before taping it in place, mark

out six “X”s from the opposing

diagonals of the four pads which

show the pushbutton switches’

positions. This will show where

the center of the large “button”

holes need to be drilled.

Similarly, mark the six LED

positions. This copy does not

need to be reversed, but you

should note that it will mount in

the box in the

bottom-left

corner. Make absolutely sure of

the positions and then tape it in

place.

The switch holes were

drilled with a 10mm (13/32in.)

drill bit and the LED holes were

drilled with a 5⋅5mm drill bit. A

larger drill bit can be used to

remove the rough edges which

occur when drilling ABS plastic,

and to provide a “concave”

finish to each of the holes. This

is best done by hand-twisting

the drill bit.

This is a very effective way

of finishing off all holes, both

outside the box and inside,

giving a neat, professional

finish. In the case of LEDs, it

can even eliminate the need for

grommets or LED clips.

IC3

k 7

POWER

D9 D10 D11

D12

a a a a a a

D8 D7

D13 D14

TR2

D15

R R R R R

11 12 13 14 15

IC1

TR3

TR4

-V

D16

1 2

To Battery

IC4

IC2

TR5

TR1

Fig.2. Printed circuit board component layout for the

Twinkle Reaction Game.

Maxfield & Montrose Interactive Inc

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PLASTIC WELDING

Many constructors will be all

too aware of how easily a slip of

the soldering iron can lead to a

ruined plastic box. The tip of the

soldering iron can thus be

equally useful in effecting what

the author calls

plastic welds.

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melting the inside of the lid also,

see Fig.3.

Be careful not to punch right

through, as that would be the

end of your box lid! Also, avoid

excessive heat as this will result

in a heat-damage warp showing

up on the outer surface. A

plastic weld takes a good few

seconds longer than a solder

“weld” to cool so a steady hand

is needed.

Having completed one

plastic weld, now perform two

further welds in a roughly

triangular configuration, Fig.3.

Your loudspeaker will be held

securely. You can, if you wish,

mount the On/Off switch using

the same plastic welding

method.

The use of your soldering

iron for welding plastic like this

will leave the iron tip in a bit of

a mess. Having wiped off as

much as possible onto a

soldering iron sponge (use the

other side of the sponge for

plastic!), switch off the iron.

When it has cooled down, the

tip of the iron can be made

good as new by rubbing it down

with an abrasive PCB polishing

block!

secure the board with the

remaining four nuts.

Before tightening up the

nuts, adjust the height of the

PCB so that the six pushbuttons

of the switches protrude from

the case by about 2mm. This

may need to be up to 3mm for

the round type of switch tops.

The On-Off slide switch, S7,

is mounted on the left-hand side

of the case, for which a small

square profile hole needs to be

drilled and filed out with a

needle file, to give a neat

appearance. Assembly is

completed by connecting and

wrapping the PP3 battery in

some tissue paper and wedging

it between the PCB and the

case lid. Screw the unit

together, and stick four rubber

feet to the base. The unit can

be finished off with some simple

rub-down lettering.

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TESTING

The circuit should work

reliably first time. If it doesn't,

the following may help solve the

problem. Test for a square

wave output from pin 3 of IC1,

which will have a very long

mark:space ratio (e.g. 100:1).If

it is there, test pin 4 of IC2

which should have a very small

mark:space ratio (e.g. 1:100).

The frequency is just over 1Hz.

The output from pin 3 of IC2

is a high frequency square

wave. If nothing is coming out

of pin 3, pull IC2 out of its

socket, carefully bend outwards

pins 4 and 5 and replace in the

socket. If an output appears, re-

bend pin 4 back into place and

test again. If the output is still

there, the fault lies around

components D15, R10, R9,

D13, D14, C4 or R8, i.e. the

voltage feedback circuit to pin 5

of IC2.

Fig.3. Suggested method of

securing the speaker to the

lid using “plastic welds”.

First, a few words of

warning.

The fumes from

melting plastic can be quite

nasty so, if you are going to

carry out this procedure for a

prolonged length of time, do it in

a well ventilated room and try to

avoid breathing in the fumes.

Using some of the plastic

swarf, which resulted from

drilling the holes in the box,

melt down three small balls of

ABS plastic. Position the

loudspeaker in its final mounting

position. Take one ball of ABS

and melt it onto the side frame

of the loudspeaker. Caress it

with the tip of the iron, towards,

and into, the ABS box lid, gently

Maxfield & Montrose Interactive Inc

ASSEMBLY

The PCB is secured to the

case lid, above the small

loudspeaker LS1, by using four

40mm long M3 bolts and 12 M3

nuts. The bolts are threaded

through the lid mounting holes

and secured by one set of four

nuts.

Next, four more nuts (one

for each bolt) are screwed onto

the bolts, but this time a space

of about 32mm should be left

between the bottom nuts to

allow the PCB to clear the

speaker. Now mount the PCB

on the mounting bolts and

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