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WHICH CLOCK?
A BINARY CLOCK!
Which clock tells the time yet has no hands,
face or digits? Which clock counts off the time in
inexorable fashion & is almost hypnotic as you
watch it? Which clock painlessly teaches binary
numbers & tells the time too? A binary clock, of
course!
Design By MICHAEL VOS*
This clock uses 17 large LEDs to
display the time in binary fashion.
Anyone who sees it remorselessly
counting away cannot help being intrigued. And while we don’t think it
will suddenly displace conventional
clocks and watches, it presents a different and interesting way of telling
the time. And it can be used to teach
the system of binary numbers.
In a binary clock, six digits are required to display seconds or minutes.
In other words, we need a 6-bit system
with each bit weighted according to
its position in the sequence. So with
six bits or six LEDs we can display
any number between zero and 63. In
70 Silicon Chip
practice, for a binary display of minutes or seconds, we only count from
zero to 59.
To display hours, we need only five
bits (or LEDs) since we need only count
up to 23. This clock will display 12 or
24-hour time.
Circuit description
Since this clock counts in binary
rather than decimal, it is ideally suited
to logic circuitry. However, rather than
use standard logic ICs, the designer
has opted to use GALs from Lattice
Semiconductors, Inc of the USA. GAL
stands for Generic Array Logic and is
a variant of the programmable logic
array devices produced by a number
of semiconductor companies.
In effect, GALs, PALs, PLAs or
whatever they are called, can be programmed by fusing internal links so
that arrays of gates can be made to
perform a wide variety of functions.
In effect, they give the advantage of
custom ICs without the design and
manufacturing expense.
Three GALs have been used in this
circuit and they have been individually programmed to provide the seconds,
minutes and hours counters. Each of
these counters can be pre-loaded with
a value using a set of DIP switches
and this provides a method of setting
the time.
With GALs providing the basic time
counting circuitry, it only remains to
provide a 1Hz pulse signal and this is
provided by IC3 and IC4.
One inverter inside IC3, a 74HC4060
ripple counter, is connected with a
crystal to oscillate at 4.194304MHz.
The crystal is temperature compensated with the ceramic capacitors
connected to pins 10 and 11. This
clock frequency is divided by 256 and
1.2k
1%
VR1
500
OUT
IC8
LM317T
120
ADJ
1%
100k
VCC
6.8
25VW
1
ZD1
4.3V
2
3
4
IN
5
6
S5 S4 S3 S2 S1 S0
S1
SECONDS
12 11 10 9 8 7
I1 I2 I3
1 2 3
5x
0.1
IC5 OUT
7805
GND
6.8
GND
25VW
6
5
7
4
8
J1
DC3
BINARY CLOCK
D1
1N4001
6.8
25VW
1
2
IN
3
12 11 10 9
M5 M4 M3 M2 M1 M0
S2
MINUTES
I1 I2
1 2
IOR1
K
A
6
IC8
IC5
I GO
8
IC7c
11
10
I3
10k
11
IC7a
2
7
3
IC7b
5
RUN
SET
S4
10k
10k
VC1
30pF
33pF
56pF
X1
4.1943MHz
10M
PO
10 8
RST
12
PI
11
4
14
6
74HC00
VCC
8
14
Q8
IC3
74HC4060
33pF
N750
12
12
RST
12
3
Q14
11
11
PI
IC4
74HC4060
16
16
VCC
13
13
IC7d
3
20
AO I
5
4
3
2
1
16
IOR4
12/ H4 H3 H2 H1 H0
24
12 11 10 9 8 7
9
I1 I2 IOR1
1 2 19 10
S3
HOURS
IOR8
K
15
IOR5
IC2
GAL16V8B
K 8
K
17
IOR3
A 4
16
LED1-5
18
IOR2
K 2
A
1
K
14
IOR6
A
1k
1k
A
1k
1k
A
I4 I5 I6 I7 I8 I9 I10
4 5 6 7 8 9 11
12
9VDC
20
VCC
19
18
IOR2
K
17
IOR3
10
16
IOR4
IC1
GAL16V8B
14
IOR6
K
15
IOR5
K
K 4
K 16
I4 I5 I6 I7 I8 I9 I10
4 5 6 7 8 9 11
IOR8
1
K
13
IOR7
12
19
18
IOR2
20
VCC
IOR1
K
17
IOR3
K 16
10
I4 I5 I6 I7 I8 I9 I10
4 5 6 7 8 9 11
12
IC6
GAL16V8B
14
IOR6
16
IOR4
K 4
K
15
IOR5
K
A 2
A 8
32
A
A 2
A 8
32
Construction
Assembly of the clock is just a matter
of installing all the components on the
PC board. This should be cleaned and
thoroughly inspected before you begin
inserting components.
Install all the resistors, diodes and
the zero-ohm link first, then insert the
crystal. Tin the case end of the crystal
with solder, install a discarded component pigtail lead through the PC board
hole at the crystal end. Solder the
wire to the crystal and PC board. This
provides a ground shield, mechanical
stability and thermal coupling to the
capacitors.
Next, install the trimmer capacitor.
The flat end goes to the left. This orientation grounds the rotor so you can
use a screwdriver without affecting
frequency adjustment.
Both 3-terminal regulators are
mounted on the copper side of the
PC board and their mounting tabs are
bolted to the board for heatsinking.
Install the three DIP switches
(S1,S2,S3) so the individual switch
numbers are on the bottom and read
from left to right. The momentary
pushbutton switch can also be installed at this stage.
IOR8
K
13
IOR7
A
1
1k
A
1k
1k
A
1k
1k
1k
LED12-17 A
1k
A
1k
1k
A
1k
1k
1k
LED6-11 A
the output at pin 14 is 16384Hz. This
is divided by IC4, another 74HC4060
ripple counter, to provide an output
signal of 1Hz at pin 3.
The outputs of the GALs directly
drive the 17 LEDs from a supply rail
which is adjustable to provide variable display brightness. The variable
supply is provided by IC8, an LM317T
adjustable 3-terminal regulator. Its ADJ
terminal can be adjusted from zero to
4.3V, as set by the zener diode ZD1,
and thus its output can be varied from
+1.2V to +4.9V.
IC5, a 5V 3-terminal regulator,
powers the rest of the circuitry and
diode D1 protects both regulators
from reversed input supply connections. Power is provided by a 9V DC
plugpack.
1k
▲
Facing page: own a binary clock & be
one up (two up) on your neighbours
who have to make do with digital or
analog clocks. 17 large LEDs indicate
the time & they are driven by GALs
(Generic Array Logic ICs).
Fig.1: the circuit is essentially in two parts: (1) an oscillator & divider chain to
produce a 1Hz signal; & (2) three GALs in a synchronous counter.
October 1993 71
Install the 17 LEDs carefully so that
they are aligned with each other. The
shorter lead of each LED goes towards
the GAL ICs.
Install ICs 3, 4 and 7 and then the
GAL ICs. Note that these are individually programmed and are coded with
paint dots on their undersides. IC1 has
one paint dot, IC2 has two paint dots
and IC6 has no paint dots.
If desired, the PC board can be
mounted on an aluminium stand using
the screws which retain the two 3-terminal regulators. This is available as
an option with the kit.
Install a PCB mount DC socket if you
want power entry from the component
side of the board. Alternatively, if
PARTS LIST
1 PC board, 303 x 101mm
1 9V 500mA DC plugpack
1 2.1mm DC socket
1 aluminium stand (optional)
3 6-way DIP switches (S1, S2,
S3)
1 momentary contact SPDT
switch (S4)
1 4.1943MHz crystal
1 500Ω trimpot (VR1)
Semiconductors
3 GAL16V8B 15ns ICs (IC1, IC2,
IC6)
2 74HC4060N ripple counters
(IC3, IC4)
1 74HC00N quad NAND gate
(IC7)
1 LM7805T 5V regulator
1 LM317 adjustable 3-terminal
regulator
17 10mm red 200mcd LEDs
(LED1-LED17)
1 1N4001 1A rectifier diode (D1)
1 79C4V3 4.3V 400mW zener
diode
Capacitors
3 6.8µF 25VW tantalum
electrolytic
5 0.1µF 50V monolithic ceramic
1 56pF N1500 ceramic
1 33pF N150 ceramic
1 33pF N1500 ceramic
1 2-30pF N750 ceramic trimmer
Resistors
1 10MΩ
1 100kΩ
3 10kΩ
1 2.2kΩ
1 1.2kΩ
17 1kΩ
1 120Ω
1 0Ω link
72 Silicon Chip
This photograph shows how the 3-terminal regulators (in this case the 7805)
are mounted & fitted with insulated standoffs for mounting the board on the
optional aluminium stand. Also shown is the panel-mounting DC power socket.
your are using the aluminium stand,
you will need to use a panel-mount
DC socket and wire it to the PC board.
Testing
Rotate trimpot VR1 fully anti-clockwise and apply 9V DC to the board
from a plugpack or power supply.
Check that the LM7805 regulator
output is +5V ±5%. Check that the
trimpot varies the LM317 regulator
output from +1.25V to +4.9V ±10%.
With the trimpot fully clockwise to
give full LED brightness, you should
see the seconds LEDs change every
second. Set all the DIP switches to the
position marked “ZERO”. Press the
pushbutton and all the LEDs should
Specifications
Clock time reference
4.194304 MHz quartz crystal.
Accuracy
±1 second per 48 days when calibrated to
within ±1Hz at 25°C.
Worst case unadjusted: ±1 second every 11
hours based on ±100Hz deviation.
Adjustment range
Approx. ±100Hz. Clockwise adjustment of
trimmer capacitor speeds up clock.
Operating temperature 0 to +50°C.
Storage temperature
0 to +85°C.
Power source
9V DC plugpack <at> 340mA min. 2.1mm DC2
type connector.
Brightness control
Variable from 0 to 30mcd per lamp.
Where to buy the kit
1.2k
LED16
2
1k
LED15
4
1k
LED14
8
1k
LED13
16
S4
1
10k
10k
10k
33pF
1k
IC6
GAL16V8B
1
LED12
32
0
S1
1
1
0.1
1
1k
LED11
1
1k
LED10
2
1k
LED9
4
1k
LED8
8
1k
LED7
16
0
S2
1
1
0.1
1
1k
LED6
32
S3
1
1
0.1
LED5
1
1k
LED4
2
LINK
IC4
74HC060
1k
0
1
33pF VC1
0.1
TP
56pF
LED3
4
1k
LED2
8
1k
2.2k
10M
IC3
74HC060
1k
X1
1
0.1
LED1
16
6.8uF
100k
6.8uF
7805
D1
GND
DC3
J1
Fig.2: the three GAL ICs are individually programmed & are coded with paint dots on their undersides. IC1 has one paint dot, IC2 has two
paint dots & IC6 has no paint dots. The two 3-terminal regulators are mounted on the copper side of the PC board.
1k
ZD1
120
IC7
74HC00
1k
LED17
1
Setting the clock
Setting the clock is a process of first setting switch
1 of DIP switch S3 for 12 or 24-hour mode. This
done, set the hours, minutes and seconds for the
appropriate time and press and hold the pushbutton
until that occurs. This can be done while you are
listening to the Telecom time signal. Having set the
time, continue to check the time signal to ensure
that the clock is in synchronism.
You can use the decimal equivalent number
shown under each LED to work out the DIP switch
settings for any value between 0 and 63. The seconds
and minutes are each set using six switches, while
five switches are used for the hours setting.
Note: the clock counting logic does not check
for valid time settings and/or valid modes on the
switches. It is possible to set the minutes and
seconds to a maximum of 63 decimal, while the
hours can be set to a maximum of 31 decimal. If
these times are indeed set up on the switches, the
clock will count until it reaches maximum, then
SC
resets to zero.
VR1
6.8uF
IC1
GAL16V8B 1 DOT
go out. Now set each DIP switch to the position
marked “ONE” and press the pushbutton. All LEDs
should light up.
Set the mode DIP switch (on S3) to “12”, set
the DIP switches for a time of 12:59:59, press
the pushbutton and one second later the LEDs
should read 1:0:0. Set the mode DIP switch to
“24”, leave the same time on the other switches,
press the pushbutton and one second later the
LEDs should read 13:0:0. Set the time DIP switches
for 23:59:59, leave the mode DIP switch at “24”
, press the pushbutton and one second later the
LEDs should read 0:0:0.
If you have a frequency counter you can adjust
the crystal exactly to frequency although the board
should be allowed to run for at least an hour before
the adjustment is made. Connect the frequency
counter to TP1. Adjust the trimmer capacitor to set
the frequency at 4.194304MHz. Note that the initial
accuracy will only be as good as your frequency
counter.
If you do not have a frequency counter, setting
the crystal for best accuracy will be a process of
trial and error, by comparing the clock with VNG
or Telecom time signals.
LM317
IC2
GAL16V8B 2 DOTS
The complete kit for the Binary Clock, including
PC board, large LEDs and programmed GAL
ICs, is available for $75 plus $5 postage and
handling from Prototype Electronics, 1/29
Stewart St, Parramatta, NSW 2150. Phone (02)
683 3510 or Fax (02) 630 3148. The optional
folded aluminium stand is also available at $25.
Note: The above price does not include a 9V
DC plugpack.
October 1993 73
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