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Items relevant to "Build An Oil Change Timer For Your Car":
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Fit this oil change
timer to your car
Can’t remember when you last changed your
car’s oil? Build this Oil Change Timer & you
won’t need to rely on your memory. It beeps a
buzzer & flashes a LED after the engine has run
for a preset number of hours.
By DARREN YATES
Keeping your car running in tip-top
condition is something that everyone
sees as an obvious necessity. However, it’s surprising to think how little
time we spend making sure of that
fact. Keeping an eye on the oil and
water levels is something everyone
is used to doing. And if you own a
VW Beetle, it’s even easier – scrub
one radiator.
72 Silicon Chip
But how often do you think of
changing the oil? Do you change it
every six months or after a set number
of kilometres? Or are you like most
people and only think about it when
the car is put in for other service work?
Regular oil changes at the recommended service intervals are vital if
engine wear is to be kept to a minimum. In fact, most car manufacturers
recommend that the oil be changed
every 6000-8000kms (or 5000 miles
for us Beetle owners). However, depending on how the car is used, that
8000kms could be chalked up in a
couple of months or it may take all
year. If you don’t keep track of the
kilometres, you have to rely on the
6-month rule and this is only a rough
guide at best.
So just how do you keep track of the
oil change intervals? If you have your
oil changed at a garage, a windscreen
sticker will serve as the reminder
although that’s easily ignored. This
electronic reminder is more insistent.
It flashes a LED and sounds an (optional) buzzer after the engine has run for
a set number of hours.
When you think about it, changing
D2
1N4004
+5V
0.1
D4
1N4004
RESET
S5
10k
3V
BACK-UP
0.1
D1
D1
1N914
1N914
11
10M
16
IC1
4060
Q14
Q14
10
3
12
11 16
RST
IC3 Q8 13
4040
4
10
Q7
CLK
2
Q6
3
Q5
+16384
+16384
4.7k
X1
32.768kHz
39pF
100k
100k
11
RST
IC2
4020
3
10 CLK
Q14
Q14
16
8
8
E
+12V FROM
IGNITION
SWITCH
GND
C
IN
OUT
A
S3
D7
S1
D8
4x1N914
D9
1N4004
F1
250mA
IN
22
25VW
K
VIEWED FROM BELOW
D6
D3
1N914
CHASSIS
ZD1
18V
1W
REG1
78L05
GND
PIEZO
BUZZER
1k
S2
8
39pF
B
10k
D5
S4
CHANGE
OIL
LED1
A
10k
B
10k
OUT
S6
K
C
Q1
BC548
E
+5V
10
16VW
OIL CHANGE TIMER
Fig.1: the circuit is based on three low-cost CMOS counter ICs (IC1-3). IC1 &
IC2 both divide the 32.768kHz clock frequency by 214, while IC3 provides four
division ratios ranging from 25 to 28 at its Q5-Q8 outputs. These outputs are
then selected by DIP switches S1-S4 to obtain the required timing period.
S1
S2
S3
S4
Timer Period
0
0
0
0
Test
1
0
0
0
36
0
1
0
0
73
1
1
0
0
109
0
0
1
0
146
1
0
1
0
182
0
1
1
0
218
1
1
1
0
255
0
0
0
1
291
1
0
0
1
328
Circuit diagram
0
1
0
1
364
Fig.1 shows the circuit diagram for
the Oil Change Timer. It uses three
low-cost CMOS ICs to do the timing
and a single transistor to beep the piezo
buzzer and flash the LED.
1
1
0
1
401
0
0
1
1
437
1
0
1
1
473
0
1
1
1
510
coupled to the clock input of IC2, a
4020 14-bit counter IC. The difference
between the 4020 and 4060 is that the
4020 doesn’t have an inbuilt oscillator.
This IC further divides the frequency
by 214, so that the output at its pin 3 is
now just 0.00012Hz. This is equivalent
to a period of 8192 seconds, or just
under 2.3 hours.
The output at pin 3 of IC2 then
couples into divider stage IC3 which
is a 4040 12-stage binary counter. We
don’t need all of the stages of division
here and only use the Q5-Q8 outputs.
These outputs are fed via a 4-way
DIP switch to diodes D8-D5 which,
together with D3, form a simple but
effective 5-input AND gate. D3 is
driven directly by the 2Hz signal
from IC1.
The timing period is set by the DIP
switches – see Table 1. Normally, one
or more of these DIP switches is closed
and so Q1’s base is pulled low by the
corresponding outputs of IC3. This
means that Q1, LED 1 and the buzzer
are all off.
At the end of the timing period, the
relevant Q outputs of IC3 go high and
so their corresponding diodes are now
reverse biased. Q1’s base is now alternately pulled high and low at a 2Hz
rate due to a 10kΩ pullup resistor and
the clock signal driving D3. Thus, Q1
pulses on and off at a 2Hz rate to flash
the LED and beep the buzzer.
Switch S6 allows the buzzer to be
1
1
1
1
546
February 1995 73
your engine oil after a set number of
hours makes a lot of sense. For example, if you spend a lot of your time
travelling in the city, your average
speed will probably be about 40km/h.
Multiply this by 200 hours and you
have your 8000kms.
On the other hand, if you do a lot
of highway driving, then you’ll clock
up the kilometres in much less time.
That’s why we’ve designed the unit
so that you can choose from a number
of presettable times from 36 to 546
hours (see Table 1). You should be
able to find one that suits your style
of driving.
The Oil Change Timer uses only
common ICs and components, most
of which you’ll probably have lying
around in your junkbox. It simply
connects to your car’s ignition switch
and to chassis. It then automatically
starts timing whenever the engine is
started and backs up the accumulated
time when the ignition is switched off
using two nicad cells.
Let’s look at Fig.1 more closely. IC1
is a 4060 14-bit binary counter with
its own inbuilt oscillator. The crystal
network on pins 10 and 11 ensures
that its frequency is 32.768kHz. IC1
divides this frequency down by 16,384
(214) so that it is just 2Hz at the Q14
output (pin 3).
This output from pin 3 is then
Table 1: DIP Switch Settings
10k
4.7k
10M
2x39pF
S1
IC1
4060
0.1
S2
1
S4
D4
IC3
4040
100k
IC2
4020
D2
1k
10uF
S3
D3
1
PIEZO
BUZZER
1
78L05
22uF
10k
10k
X1
10k
D8 D7 D6 D5
D1
Q1
D9
12V
FROM IGN
0.1
ZD1
S6
S5
3V BACKUP
BATTERY
K
A
LED1
Fig.2; make sure that all polarised parts are correctly oriented & note that
the positive connection to the ignition switch must be run via a 250mA in-line
fuse. The buzzer & switch S6 can be regarded as optional.
switched out of circuit after it has
sounded, to prevent annoyance. However, the LED continues to flash until
the circuit is reset and this is done by
pressing S5 to reset counters IC2 and
IC3 (ie, when the oil is changed).
If all four DIP switches are open,
the 2Hz signal from IC1 is fed straight
to Q1 which means that the LED
flashes (and the buzzer sounds) as
soon as power is applied. This is
useful for checking that IC1, Q1, LED
1 and the buzzer are all operating
correctly.
Note also that once the LED starts
flashing, it will continue flashing for a
period equal to the current time setting
(unless the Reset switch is pressed).
This means that if you set the unit to
146 hours, for example, the LED will
flash for another 146 hours, or until
the reset button is pressed.
Power supply
Power for the Oil Change Timer is
derived from the ignition switch and
is fed to a 78L05 3-terminal regulator via fuse F1 and reverse-polarity
protection diode D9. ZD1, an 18V
1W zener diode, limits any high
voltage spikes that may appear on
the line due to the operation of other
equipment.
The 7805 regulator delivers a +5V
rail and this is filtered using a 10µF
electrolytic capacitor. This rail then
directly powers the buzzer and LED
circuitry, while the ICs are powered
via isolation diode D2.
D4, a 10kΩ resistor and two nicad
cells form the battery backup circuit
(you could also use two alkaline batteries if you prefer). When the ignition
is on, D2 is forward biased and the
nicad cells are trickle charged via the
10kΩ resistor. Conversely, when the
ignition is off, D4 is forward biased
and the backup battery provides power
to the three ICs.
Note that although the minimum
operating voltage of CMOS 4000 series
ICs is quoted as 3VDC, we’re only
using a nominal 2.4V rail here due to
the voltage drop across D4. However,
we’ve found that a CMOS counter IC
will remember its internal count even
when the supply rail drops down to
as low as 1VDC.
At this voltage, you don’t get any
output level and they won’t advance
the count if you try to clock them.
However, the applied voltage is
enough to keep the internal flipflops
powered up so that they remember
their current settings.
The other interesting point to note
here is that the quies
cent current
is only about 0.2µA. As a result,
the voltage developed across D4 is
only about 100mV and not the more
normal 600mV. This low quiescent
current also means that the backup
battery will last for the length of its
shelf life.
To preserve the counts in IC2 and
IC3, it is also necessary to disable
IC1’s oscillator when the ignition is
switched off. This is done using diode D1. When the ignition is on, D1
is reversed biased and the oscillator
operates in its normal fashion. However, when the ignition is switched
RESISTOR COLOUR CODES
❏
❏
❏
❏
❏
❏
No.
1
1
4
1
1
74 Silicon Chip
Value
10MΩ 5%
100kΩ
10kΩ
4.7kΩ
1kΩ
4-Band Code (1%)
brown black blue gold
brown black yellow brown
brown black orange brown
yellow violet red brown
brown black red brown
5-Band Code (1%)
not applicable
brown black black orange brown
brown black black red brown
yellow violet black brown brown
brown black black brown brown
PARTS LIST
1 PC board, code 05102951,
102 x 56mm
1 plastic case, 130 x 68 x 41mm
1 front panel label, 127 x 63mm
1 momentary NO pushbutton
switch
1 SPDT toggle switch
1 mini piezo buzzer (7.5mm pin
spacing)
1 in-line fuseholder & 250mA
fuse
2 AA nicad cells
1 2 x AA cell holder
1 battery snap connector
1 4-way DIP switch
1 32.768kHz watch crystal
The batteries can be secured inside the case by wrapping them in foam rubber &
then sandwiching them between the board & the lid when the lid is closed. The
4-way DIP switch allows 16 possible settings between 36 hours & 546 hours. In
general, the lower settings will be suitable for cars, while the high settings can
be used for stationary engines.
Semiconductors
1 4060 14-bit counter/oscillator
(IC1)
1 4020 14-bit counter (IC2)
1 4040 12-bit counter (IC3)
1 78L05 3-terminal regulator
1 BC548 NPN transistor (Q1)
1 18V 1W zener diode (ZD1)
3 1N4004 diodes (D2,D4,D9)
6 1N914 signal diodes
(D1,D3,D5-D8)
1 5mm red LED (LED 1)
4 12mm x 3mm-dia. machine
screws plus 8 nuts
off, D1 becomes forward biased and
pulls pin 11 of IC1 down to 0.6V. This
stops the oscillator and so no further
clock pulses are produced to clock
IC2 and IC3.
mounted with its ON position towards
diodes D5-D8. The buzzer must be
mounted with its positive terminal
adjacent to the edge of the PC board
–see Fig.2.
Capacitors
1 22µF 25VW electrolytic
1 10µF 16VW electrolytic
2 0.1µF 63VW MKT polyester
2 39pF ceramic
Construction
Final assembly
All the components for the Oil
Change Timer are installed on a PC
board measuring 102 x 57mm and
coded 05102951. Before you begin
construction, check your etched board
carefully against the published pattern
to ensure that there are no shorts or
breaks in the tracks. If you find any,
use a small artwork knife or a touch of
your soldering iron where appropriate
to fix the problem.
Fig.2 shows the layout on the PC
board. Begin by installing PC stakes at
the eight external wiring points, then
mount the remaining parts as shown.
Leave the DIP switch and the buzzer
until last and take care to ensure that
the semiconductors are all correctly
oriented.
Note that the pins on the 4-way DIP
switch can be somewhat flimsy so be
careful not to break them. It should be
The prototype board was housed
in a small plastic case but this can be
considered optional. In a practical installation, you might elect to wrap the
PC board in foam and hide it behind
the dashboard. That way, the LED and
the two switches could all be mounted on a small satellite panel situated
somewhere on the console.
You could even elect to delete the
buzzer and toggle switch altogether
and just settle on the flashing LED to
provide the oil change indication.
If you do elect to mount the unit
in the specified case, then proceed
as follows. First, use the board as a
template for marking out and drilling
its mounting holes. This done secure
the board in position using machine
screws and nuts, with an additional
nut under each corner serving as a
spacer.
Resistors (1%, 0.25W)
1 10MΩ 5%
1 4.7kΩ
1 100kΩ
1 1kΩ
4 10kΩ
Miscellaneous
Light-duty hook-up wire, auto
motive cable (for power supply
connections), automotive connect
ors, heatshrink tubing.
Once the board is in position, drill
a 6mm hole in the side of the case
adjacent to the buzzer to allow the
sound to escape. An additional hole
is also required in one end of the case
to accept the ignition switch leads.
The front panel artwork can now
be affixed to the lid and the holes
drilled for the warning LED and the
two switches.
Complete the construction by
February 1995 75
OIL CHANGE
TIMER
OIL WARNING
RESET
mounting the front panel items and
running the wiring as shown in Fig.2.
You can use light-duty hook-up wire
for this job. Take care with the orientation of the LED; its anode lead is the
longer of the two (see Fig.1).
Take care also to ensure that the
leads to the battery snap connector
are wired with the correct polarity.
This clips onto a 2-AA cell holder.
The ignition leads should be run using
medium-duty automotive cable.
Before you screw the lid down,
connect the circuit to a 12VDC source.
This can be either a power supply or a
12V battery. With all of the DIP switches open, the LED and buzzer should
start immediately and should pulse
on and off at 0.5-second intervals. The
supply voltage on pin 16 of each IC
should be about 4.4V.
Setting the DIP switches
Assuming everything works correctly, you can set the DIP switches to give
ALARM ON
The 4-way DIP switch is used to set
the required timing period. Refer to
Table 1 for the various settings – there
are 16 combinations to choose from.
the required number of hours. Table
1 shows the period provided by each
combination.
In fact, you might want to give yourself a trial period over a few days to
arrive at a reasonable average speed.
This is easy to do. Just set your odo
meter to zero and keep a record of your
driving periods over the next few days.
Fig.4: check your PC board against this full-size etching pattern
before mounting any of the parts.
76 Silicon Chip
Fig.3 (left): this full-size artwork
can be used as a drilling
template for the front panel.
Alternatively, you can mount
the board under the dashboard
somewhere & simply mount the
switches & the warning LED on a
small panel.
You can then use the odometer
reading and the accumulated
period to calculate your average
speed. From there, you can then
calculate the number of engine
hours it will take to cover the
required distance.
An example will serve to demonstrate this. Let’s say that, over several
days, you cover a total distance of
400km in an accumulated time of 12
hours. In that case, your average speed
will be 400/12 = 33.3km/h. If we now
assume an oil change service interval
of 7500km, then the approximate
number of engine hours required to
cover this distance will be 7500/33.3
= 225.2 hours.
If we look now at Table 1, we see
that 218 hours is the closest available setting. To obtain this setting, we
simply leave S1 & S4 off and set S2
& S3 on.
Installation
The unit is relatively easy to install,
since there are only two external wiring connections. One connection goes
to chassis, while the other goes to the
switched side of the ignition switch.
The latter connection is best made at
the fuse panel and should be run via
a 250mA in-line fuse. Alternatively,
you can run this lead to the ignition
switch via one of the accessory fuses
(eg, for the car radio).
Do not leave out the fuse; it is a
necessary safety precau
tion in the
event of a short inside the unit. Also,
make sure that you install all wiring
in a professional manner and use automotive connectors and heatshrink
tubing to terminate the leads.
Finally, you must press the reset
button the first time the unit is powered up, to make sure that the counters
start from scratch. After that, the reset
button is pressed only when the engine
oil is changed. For this reason, you
might like to mount the reset button
in some inconspicuous location, away
SC
from prying fingers.
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