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The Ol’ Timer: an
alphanumeric clock
with old-fashioned time
Are you tired of looking at those boring digital
clocks or at those drab looking old tickers hang
ing on the wall? Then grab onto this old-time
clock using newfangled technology.
By ANTHONY NIXON
There have been all sorts of clocks
designed over the years but none actually show you the time in its most basic
form – the way you think it. But now
you can build the Ol’ Timer. It shows
you the time just the way we all used
to say it and think it and no doubt still
do. It’s easy to read and can be used
20 Silicon Chip
as a teaching aid for those people who
find it difficult to understand the usual
types of clocks.
To show how different this clock
is, let’s give a few exam
ples of its
time displays. At 12.00 AM it displays “MIDNIGHT”; at 1:15, it shows
“1/4 PAST 1”; at 12.00 PM, it shows
“NOON”; at 3:35, it shows “25 TO 4”
and so on. In other words, it displays
the time in more or less the same way
as you would think it or say it.
Some of the photos in this article
give further examples of its time displays. Note that it will also display
time in standard digital format if you
want it to.
To provide this alphanumeric display of time, the circuit uses eight LED
dot matrix (5 dots across by 7 dots
vertically) displays. These displays
are driven in multiplex fashion by
a microcontroller to keep the circuit
complexity to a minimum.
Apart from ol’ time telling, this
R13
220
R14
10k B
D2
1N914
E
1
RTCC
Q2
BC557
C
28 MCLR
RA0
RB7
17
2
8
SB CLK
BUZZER
RA3 9
R8
10k
C
Q3
BC548
B
R5
10k
A
S2
20 RC2
19
RC1
18
RC0
RB2 12
RB3 13
RB4 14
RB5 15
R11
150k
R12
39k
R9
100k
RB6 16
3
4
LDR1
2
13
5
IC6
2003
6
7
11
DISPLAYS
10
15
2
1
16
+5V
7
D1
1N4001
6 24 RC6
4
RC7
27
X1
8MHz
C1
18pF
12
8
IC8
741
R10
100k
7
14
+5V
3
2
8
SB CLK 14
1
IC5
SA
74HC164
9
CLR
A B C D E F G H
C8
3 4 5 6 10 11 12 13 0.1
R17-56
40x130W
RB0 10
RB1 11
R7
10k
FROM
PIN13 IC4
TO PIN2
IC2
9
1
SA CLR
A B C D E F G H
3 4 5 6 10 11 12 13
IC7
PIC16C57
B
S3
R6
10k
14
IC1
74HC164
7
E
MODE
S1
+5V
6
R15
33k
ZD1
3.3V
C4
0.1
C3
0.1
2
R3
2.2k 26
C2
18pF
LED1
ALARM
R16
10k
B
21
RC3
22
R1
RC4
470k
23
RC5
RA1
SP1
BZW04P13B
7
OSC1
OSC2
RA2
8
R2
2.2k
25
RELAY1
4
R4
2.2k
LED2
PM
OL' TIMER
B
C
Q1
BC548
E
Circuit description
The circuit is based on the PIC
16C57 microcontroller which has 2Kb
of ROM, 72 bytes of usable RAM and
20 I/O ports. It takes care of all of the
clock functions which include display
multiplexing, key scans, display dimming, timing, LED indication and relay
and buzzer control.
The chip is clocked using an 8MHz
crystal which is divided by four
internally to provide an instruction
E
B
VIEWED FROM BELOW
E
C
A
K
I GO
A
7.5V
WO4
240VAC
N
IN
7V
E
Fig.1: the heart of the circuit is the PIC57 microcontroller which is programmed
to drive the LED dot matrix displays. Serial data is fed from pin 17 of IC7 &
converted to 40-bit wide words (ie, parallel data) by shift registers IC1-IC5. Note
that IC2, IC3 & IC4 are not shown since they are cascaded between IC1 & IC5.
clock features date, alarm, 99 minute
timer, buzzer or relay control, daylight
saving, digital format, sleep timer, leap
year indicator, display dimming and
power failure indication.
C
cycle time of 500 nanoseconds. This
is further divided by 64 with a programmable prescaler to give a clock of
31.25kHz. This is used to increment
an internal Real Time Clock Counter
(RTCC) which, when initialised to
206, will overflow to 0 in 1.6ms. This
is used as a timebase to update the
display. This frequency is further
divided by four for key scanning and
other timing functions.
Every 1.6ms, serial information from
the display buffer inside the micro
controller is sent from pin 17 of IC7
to the serial input of IC1, the first of
five 8-bit serial to parallel converters
which are cascaded to receive 40 bits
of information. These ICs are actually
C9
470
25VW
REG1
7805
GND
OUT
+5V
C10
47
16VW
74HC164 serial in/parallel out shift
registers.
Note that only IC1 and IC5 of this
40-bit converter string are shown on
the circuit diagram but you will see
that pin 13 of IC1 goes to pin 2 of IC2
and hence pin 13 of IC2 goes to pin 2
of IC3 and so on.
What happens is that a 40-bit serial
data stream is sent out from pin 17
of IC7 and as it is being sent out, it
is clocked through the registers by a
clock signal from pin 6 of IC7 to the
register clock inputs (pin 8).
Thus, the 40-bit serial data stream
is converted to a 40-bit wide word
which appears on the Q outputs of
the registers. These drive the column
inputs of the eight dot-matrix displays
via 130Ω resistors.
The seven row inputs of the dot
matrix displays are driven by IC6, a
November 1994 21
RELAY
1
10k
BROWN
BLUE
D1
Q1
SP1
TERMINAL
BLOCK
ACTIVE
BROWN
NEUTRAL
BLUE
EARTH
GREENYELLOW
1
2.2k
1
MAINS
CORD
2.2k
1
2.2k
MAINS
CABLE
CLAMP
1
40x130W
X1
18pF
18pF
10k
DISPLAY6
470k
IC7
16C57
0.1
10k
IC4
74HC164
10k
1
Q2
10k
10k
0.1
S1
DISPLAY7
IC6
2003
DISPLAY1
IC1
74HC164
7.5VAC
1
DISPLAY2
0.1
0.1
IC3
74HC164
33k
POWER
TRANSFORMER
DISPLAY3
IC2
74HC164
DISPLAY5
220
0.1
100k
D2
ZD1
Fig.2: the wiring diagram shows both patterns for the PC board. The dark grey
pattern is on the underside while the light grey pattern is on top of the board.
Take care to ensure that all parts are correctly oriented.
1
K
LDR1
K
Q3
A
39k
BUZZER
7VAC
470uF
REG1
O
G
1
WO4
LED2
A
LED1 47uF
100k
IC8
741
S2
0.1
DISPLAY8
IC5
74HC164
150k
22 Silicon Chip
DISPLAY4
S3
This is the view inside the clock with the rear panel (case lid) removed. Make
sure that the mains cord is securely clamped & note that the Earth lead (green/
yellow) must be soldered to a solder lug that’s secured by one of the transformer
mounting screws. The Active & Neutral leads go to a 2-way terminal block.
7-way Darlington array which is driven in turn by seven output lines from
the microcontroller. The displays are
multiplexed in such a way that each
time a row is enabled via IC6, the
column lines from ICs 1-5 are updated. Thus, the LEDs are driven with a
duty cycle of 14%; ie, 1.6ms on and
9.6ms off.
By way of further explanation, the
LED dot matrix displays are common
cathode types with the cathodes
of each row being pulled to 0V by
Darlington transistors in IC6 and the
anodes driven by the registers, IC1-IC5.
In other words, the registers “source”
current into the displays while IC6
sinks the current.
Actual clock timing is derived from
the 50Hz AC mains supply. This is
supplied from the 7.5V winding of
the transformer via a 470kΩ resistor.
A transient suppressor is connected
across the output from this winding
to shunt any spike voltages and thus
protect IC7. The AC signal is clamped
to the positive and 0V rails because of
the internal protection diodes fitted
to all I/O pins on the chip. These are
capable of withstanding several milli
amps of current, much more than can
be supplied via the 470kΩ resistor.
Transistor Q2 forms a “Brown Out”
protection circuit. When the supply
voltage falls below about 4V, this
transistor will cease to conduct and
the master clear (MCLR), pin 28, will
be pulled low via the 33kΩ resistor,
causing the chip to reset. The chip has
internal circuitry which controls all of
its resetting functions.
Display dimming is achieved using
IC8, a 741 op amp which has a light
dependent resistor connected to its
pin 3. When the ambient light level
drops below a certain level, IC8’s
RESISTOR COLOUR CODES
❏
No.
❏ 1
❏ 1
❏ 2
❏ 1
❏ 1
❏ 6
❏ 3
❏ 1
❏
40
Value
470kΩ
150kΩ
100kΩ
39kΩ
33kΩ
10kΩ
2.2kΩ
220Ω
130Ω
4-Band Code (1%)
yellow violet yellow brown
brown green yellow brown
brown black yellow brown
orange white orange brown
orange orange orange brown
brown black orange brown
red red red brown
red red brown brown
brown orange brown brown
5-Band Code (1%)
yellow violet black orange brown
brown green black orange brown
brown black black orange brown
orange white black red brown
orange orange black red brown
brown black black red brown
red red black brown brown
red red black black brown
brown orange black black brown
November 1994 23
depending on the display requirements and ranges from around 30mA
to 200mA.
Mechanical details
The displays are mounted on the underside of the PC board & are attached to it
using individual pin sockets (see text). The LDR enables dimming of the display
at night while the two LEDs indicate the alarm mode & PM.
output swings high. When the micro
controller detects this high, it cuts the
duty cycle of the displays to 50% of
their normal operation, thus dimming
the display. The 150kΩ resistor from
pin 6 to pin 3 provides some hysteresis
and stops IC8’s output from oscillating
when the light level is at the changeover point.
The three pushbutton switches are
read via inputs RC0-RC2 (pins 18, 19
& 20) and are debounced using software delays. IC7’s outputs RA1 and
RA2 drive the PM and ALARM LEDs
directly, while outputs RA3 and RC7
drive the buzzer and relay via Q3 and
Q1 respectively.
Average current consumption varies
The Ol’ Timer clock is housed in a
standard black plastic jiffy box measuring 196 x 112 x 65mm. The box is
stood on its side and has a red Perspex
window for the dot matrix displays.
All the circuitry is mounted on a
double-sided PC board measuring 145
x 90mm. The PC board doesn’t have
plated through holes but uses IC pin
sockets soldered to the board to complete the connections. These are used
to mount the eight dot matrix displays
on the underside of the board.
The easiest way to solder these pins
neatly is to place them on a 6-pin IC
strip, then place them into the board
holes and solder them. When the strip
is removed, the pins are left looking
tidy and with the correct spacing.
These pins can be knocked out
from 2 x 64 machine pin IC sockets.
Some pins on the IC sockets don’t
pass through the circuit board but are
bent at right angles and soldered to
the component side of the board. The
track layout has been designed for
this purpose.
A quick method of knocking these
PARTS LIST
1 double-sided PC board, 181 x
112mm
1 plastic Jiffy case with plastic lid,
196 x 113 x 65mm
1 transformer 7V CT + 7.5V; DSE
Cat. M-2824
1 5V SPDT relay; Ritronics Cat.
S-14100
1 piezoelectric buzzer; Jaycar Cat.
AB-3460
3 momentary contact pushbutton
switches; Jaycar Cat. SP-0710
1 8MHz crystal
1 piece of red Perspex, 180 x
95mm
2 rubber feet
1 3-core mains cord & plug
1 2 way insulated terminal block
1 cable clamp to suit mains cord
1 solder lug
2 10mm PCB spacers
13 PC stakes
96 IC pins (from 2 x 64 machine
pin IC sockets)
24 Silicon Chip
IC sockets
5 14-pin
1 16-pin
1 8-pin
1 28-pin
Semiconductors
5 74HC164 8-bit shift registers
(IC1-5)
1 2003 Darlington array (IC6)
1 16C57 preprogrammed
microcontroller (IC7)
1 741 op amp (IC8)
1 7805 5V regulator (REG1)
2 BC548 transistors (Q1,Q3)
1 BC557 transistor (Q2)
1 3.3V 400mW zener diode
(ZD1)
1 1N4001 diode (D1)
1 1N914 diode (D2)
1 WO4 bridge rectifier
8 7 x 5 Sun MUR18A dot-matrix
column anode LED displays;
C & K Electronics
1 light dependent resistor; Jaycar
Cat. RD-3480 (LDR1)
1 BZW04P13B transient
suppressor; Farnell Electronics
(SP1)
2 3mm red LEDs (LED1,2)
Capacitors
1 470µF 25VW PC electrolytic
1 47µF 16VW PC electrolytic
6 0.1µF 63VW MKT polyester
2 18pF ceramic
Resistors (0.25W 1%)
1 470kΩ
6 10kΩ
1 150kΩ
3 2.2kΩ
2 100kΩ
1 220Ω
1 39kΩ
40 130Ω
1 33kΩ
Miscellaneous
Tinned copper wire, insulated hookup wire, machine screws, nuts &
washers, right-angle mounting
bracket for piezo buzzer, heatshrink
tubing.
The three pushbuttons on the rear of the case allow selection of the various
operating modes, time setting, alarm setting & so on.
This close-up view shows the method
of mounting the LED matrix displays.
Each display is plugged into 12
machined IC pins. Take care to
ensure that the displays are correctly
oriented (the pins are polarised)
The piezo buzzer is mounted on a
small L-shaped metal bracket on the
side of the case.
The OL’ TIMER is an old-fashioned clock in the way it shows the time, although
old-fashioned clocks never did it like this. It uses LED dot matrix displays
driven by a PIC57 microcontroller.
pins out of the socket carrier is as
follows. First, a piece of round steel,
3mm in diameter, is cut to a length of
25mm or so. This done, drill a 1mm
hole into one end, 5mm deep. This tool
is then placed over the pin and tapped
lightly with a small hammer. No pins
are damaged in this way. It’s a neat idea
to create a pseudo through-plated hole
when a socket is required.
Board assembly
In other respects, the PC board is
quite straightforward to assemble.
Sockets for the ICs are listed in the
parts list and are recommended. Note
that six 0.1µF capacitors are shown in
the parts list but only three are shown
on the circuit. The other three are associated with shift registers IC2, IC3 and
IC4 which are also not on the circuit,
as noted above.
Note that in most cases the resistors
are soldered only on the underside
of the board. The 40 130Ω resistors
associated with the five shift register
These are just three more displays from the OL’ TIMER. It can display the date & conventional digital time as well.
November 1994 25
Operating Instructions
Using the Ol’ Timer clock is fairly
straightforward. Just use the MODE
key to select a function and then use
either the A or B keys to change the
settings. After changing a setting or
a function, the clock will revert back
to the selected time display if no
keys are pressed for three seconds.
It can also be cycled back using the
MODE key.
If button A or B is held down, that
button’s function will be repeated
slowly at first and then at a faster
rate.
Setting the time & alarm: use the
MODE key to select the time setting
function. Then by pressing either A
or B, the hours or minutes will be
incremented respectively. Setting the
alarm time is accomplished in the
same manner.
Setting the date: use the MODE key
to select the date display and press
A to select either the day, month or
year. Then press B to increment the
selection. If the year is a leap year,
the LED at the lower right-hand corner of the display will light when the
complete date is being displayed.
Using the 99 minute timer: select
ICs are stood on end to save space.
Take careful note of the orientation
and polarity of the ICs, diodes, transistors and electrolytic capacitors. PC
pins should be installed for all the
off-board connections.
Once the board is complete, you will
need to make a cutout in the base of
the box for the display and drill other
holes that are required. The rectangular hole for the display measures 115 x
20mm and will need to be positioned
precisely to line up with the dot matrix
displays. The circuit board is secured
using two 10mm tapper spacers fas-
the timer display with the MODE
switch. The number displayed indicates the time in minutes for the timer
to count down from, after which the
buzzer will sound or the relay will
operate. This time can be increased
by pressing B or decreased by
pressing A.
Use MODE to set the output configuration for the timer. If BUZZER is
selected, then it will sound for five
seconds after the timer counts down
to zero. If the relay is selected, it can
either operate ‘While’ (indicated by
“RELAY=W”) the timer is counting
down or ‘After’ (indicated by “RELAY=A”) it has finished.
Press A to select either BUZZER or
RELAY. If RELAY is selected, press B
to chose the ‘While’ or ‘After’ option.
The relay can be turned off at any
time by pressing B while the display
is showing normal time.
Using the alarm: after the alarm
time has been set and the display is
showing normal time, pushing button
B sets the alarm. The ALARM LED
now lights. When the normal time
equals the alarm time the buzzer
will beep for 1 hour. If the A button
tened to the base of the jiffy box by
two countersunk screws.
These screws are concealed by
the red Perspex which becomes the
front panel of the clock. The Perspex
was attached to the box by a pin in
each corner and these are secured
inside the box with 5-minute epoxy
adhesive.
Note the details for connection of
the mains cord. This should be anchored to the side of the case as shown
in the wiring diagram and the Active
and Neutral wires terminated to a
2-way insulated terminal block which
Where to buy the microcontroller
The programmed PIC57 microcontroller is only available from the author,
Anthony Nixon, who can also supply the double-sided PC board and a set
of machine pins (see text). Pricing is as follows:
(1). PIC57 programmed microcontroller, $30.00 including p&p;
(2). PIC57 plus PC board and set of machine pins, $47.00 including p&p.
Send cheque or postal money orders to Anthony Nixon, 20 Eramosa Road
East, Somerville, Vic 3912.
26 Silicon Chip
is pushed, the buzzer will be silenced
for 10 minutes and then resound. The
ALARM LED flashes while the ‘Sleep’
function is operating. This function
can be continued for 1 hour. If A is
pressed while the sleep function is
operating, then the buzzer will stop
until the two times match again. If B
is pressed, the buzzer will stop, the
alarm will be disabled and the ALARM
LED will extinguish.
Setting daylight saving time: press
MODE until ‘DLS = ’ is displayed.
Daylight saving is enabled if ‘DLS =
Y’ is displayed, or disabled if ‘DLS =
N’ is displayed. When enabled, the
normal time is increased by one hour
and decreased by one hour when
disabled. All dates are updated in
the process. Use A to enable/disable.
Display format: the last function
selects the display format. Press A
to alternate between OL’ TIME and
DIGITAL formats.
Power failure indication: when the
clock is first turned on or if there has
been a power failure, the display will
flash “OL’ TIMER” on and off. You
then must reset all time and alarm
settings.
also terminates the primary windings
of the transformer.
The Earth wire of the mains cord
is terminated at a solder lug which
is secured to one of the transformer’s
mounting lugs.
A small bracket will need to be
made up to mount the piezo buzzer,
as shown in the photos. Ventilation
holes should be drilled in the rear
panel, as well as the holes for the
three pushbutton switches and the
cord entry.
Initial tests
When all assembly work is complete, carefully check your work and
then apply power. The display should
flash ‘OL TIMER’ on and off. Check
the 5V supply rail from the regulator.
If any LEDs fail to light , it is quite
easy to determine which row and
column they are in and then check for
open circuits in the board connections.
Assuming that all is well, the correct
time can now be set as detailed in the
SC
operating instructions.
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