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Items relevant to "Beginner's Dual Rail Variable Power Supply":
Items relevant to "Build A Talking Headlight Reminder":
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Build this talking
headlight reminder
Ever leave your car’s headlights or parking
lights on? Flatten the battery too? If so, you
need this talking headlight reminder. If you
accidentally leave your headlights on, it tells
you to switch them off.
By DARREN YATES
Most headlight reminders are quite
simple devices. Typically, they sound
a beeper if the ignition is switched off
while the headlights are still on. In
some cars, the beeper is not activated
until a door is opened but regardless of
the triggering method used, a headlight
reminder can save you from a great
deal of inconvenience.
Of course, if you drive an old car,
then it’s quite probable that is lacks
this very useful feature. This Talk-
ing Head
light Reminder is actually
far more elaborate than a headlight
reminder needs to be but it’s easy to
build and it has one big advantage over
other such units – you can record your
own message. After all, what could be
more attention-getting than “you’ve
left yer lights on stupid”, or something
equally hard hitting?
The recorded message is continually replayed over a 30-second period,
after which the device automatically
switches itself off.
The heart of the Talking Headlight
Reminder is a 16-second sound recorder IC, the ISD1416 from Information
Storage Devices. This is a second
generation device and is based on
the original ISD1016 which we used
in the 16-Second Message Recorder
described in July 1993.
Like the original device, the ISD1416
features 16 seconds of recording time
but now has the added features of
optional edge-level control and automatic power down. Edge-level control
simply means that playback can be
initiated by momentarily pressing the
PLAY button, although that feature is
not used here.
Power for the circuit is supplied
via the headlights switch, while the
trigger input monitors the ignition
switch. The sound comes from an
external speaker and this can be
October 1994 37
INTERNAL
CLOCK
XCLK
MIC
MIC REF
AGC
DECODERS
AMP
ANA OUT
ANALOG
TRANSCEIVERS
ANTIALIASING
FILTER
ANA IN
PREAMP
pling rate. The signal is then sampled
and stored in the EEPROM array, ready
for playback.
During playback, the stored samples
are clocked out of the EEPROM array
and passed through a 5-pole smoothing filter. The recovered signal is then
fed to an internal audio amplifier and
this can either drive a small loudspeaker directly or an external power
amplifier.
Thankfully, the circuitry inside the
IC takes care of all the difficult jobs
such as providing clock signals and
sampling rates. All we have to do is
apply the signal, make sure that the
correct lines are either high or low,
and that’s about it.
SAMPLING
CLOCK
TIMING
SP+
SMOOTHING
FILTER
SP-
AMP
128K CELL
NONVOLATILE
ANALOG STORAGE
ARRAY
AGC
POWER
CONDITIONING
VCCA
VCCD
ADDRESS BUFFERS
DEVICE CONTROL
A0 A1 A2 A3 A4 A5 A6 A7
REC
PLAYE
PLAYL
RECLED
Fig.1: this block diagram shows the main components of the ISD1416 sound
recorder IC. It uses a 128K-cell EEPROM to store up to 16 seconds of audio in
analog form, a technique that eliminates the need for A/D & D/A converters.
mounted either under the dashboard
or under a seat.
OK, that’s just one application for
this device. It could be used anywhere you need a solid-state message
recorder that re
p eats a recorded
message over a 30-second interval.
All you have to do is connect the
appropriate supply voltage and trigger input.
ples the incoming audio signal and
stores the samples as analog voltages
in a 128,000-cell EEPROM (electric
ally erasable programmable read-only
mem
ory). This technique provides
much better sound quality than can
be obtained from a similar digital device and means that the recording is
retained in memory when the power
is removed. And because the information is stored in the EEPROM in analog
form, there’s no need for A/D and D/A
converters.
In greater detail, the incoming audio
signal is amplified and fed through a
5-pole anti-aliasing filter to remove
frequencies greater than half the sam-
Sound storage
Refer now to Fig.1. This shows the
block diagram of the ISD1416 and
we’ll go over the principles of this
chip briefly.
During recording, the device sam-
How it works
Let’s now take a look at the circuit
for the Talking Headlight Reminder
–see Fig.2. As you can see, there are
just three ICs involved: a 555 timer
Fig.2 (below): the circuit is based on
the ISD1416 sound recorder (IC2). If
the ignition is switched off before the
lights, IC1 turns Q1 on for 30 seconds
& IC2 repeats the recorded message
until the timing period ends. IC3 is the
audio amplifier stage.
D2
1N4004
REG1
78L05
OUT
GND
1k
1k
0.1
10k
RECORD
LED1
0.22
A
K
18
0.22 17
10
16VW
MIC
24
25
PLAYE
MIC
MIC
REF
RECLED
1M
100k
FROM
IGNITION
SWITCH
1k
D1
1N4004
100k
7
6
0.1
PLAY
S1
Q1
BC548 C
4
8
3 100k B
REC
S2
IC1
E
555
5
2
1
22
25VW
0.1
B
E
C
E
B
C
VIEWED FROM BELOW
TALKING HEADLIGHT REMINDER
38 Silicon Chip
IN
CHASSIS
OUT
100
16VW
1
14 1k
20
GND
REG2
7809
100k
27 REC
23
AIN
PLAYL
1
A0
AOUT
2
A1
3 A2
XCLK
5
A4
6
AGC
A5
VSSD VSSA
12
13
V+
FROM
HEADLIGHT
SWITCH
100
16VW
28
VCD 16
VCA
A3 4
9
A6
10
A7
IC2 SP+
ISD1416
10k
IN
1
VOLUME
VR1
10k
6
3
IC3
2 LM386
7
21 4.7k
10
16VW
5
4
100
8W
EXT.
SPKR
0.1
10
26
19
470k
4.7
25VW
A
K
I GO
I GO
LED1
MIC
100k
100uF
1uF
1k
REG2
100uF
0.22
IC3
LM386
1
IC2
ISD1416
0.1
TO
IGNITION
SWITCH
1
S1
(IC1), the ISD1416 (IC2) and an LM386
audio power amplifier (IC3).
D1, IC1 and transistor Q1 form the
playback trigger circuit for IC2. If the
headlights are off when the ignition is
switched off, nothing happens since
no power is applied to the circuit.
However, if the ignition is switched
off first, D1 is forward biased (since
its cathode is pulled low) and a short
Below: the PC board is mounted on
the back of the lid using 19mm long
spacers & secured using machine
screws & nuts. Note the method used
to mount the two switches.
S2
470k
1uF
D1
TO SPEAKER
TO SPEAKER
CHASSIS
1k
100k
100k
D2
+V FROM LIGHT SWITCH
0.1
4.7k
22uF
1k
100uF
VR1
10
1
REG1
0.1
10k
0.22
Fig.2: install the parts on the PC board
as shown here, taking care to ensure that
all polarised components are correctly
oriented. The two pushbutton switches
(S1 & S2) are mounted by soldering their
pins to the tops of PC stakes (see photo
below).
K
1k
10uF
0.1
IC1
555
10k
Q1
100k
1M
A
4.7uF
negative-going pulse is applied to pin
2 (the trigger input) of IC1.
IC1 is wired in monostable configuration. When triggered, its output at
pin 3 goes high for approximately 30
seconds. This turns on transistor Q1
which in turn pulls the PLAYL input
(pin 23) of IC2 low.
PLAYL stands for “PLAY LEVEL”,
which indicates that it is a level-triggered input rather than an edge-triggered one. Thus, IC2 only plays back
the recorded message during the
30-second period that Q1 is on (ie,
for as long as the PLAYL input is held
low). Note that the address lines (A0-
A5) of the ISD1416 are all connected
to ground. This places the device into
“loop” mode, so that the recorded
message is repeatedly replayed during
the 30-second period.
Alternatively, IC1 (and thus IC2)
can be manually triggered by pressing switch S1 (PLAY). Normally, this
switch would not be used once the
device is installed in a car. It’s there
simply to provide a convenient way of
triggering the recorded message during
the setting up procedure.
The audio output from IC2 appears
at pin 14 and is AC-coupled to pin 2
of IC3, an LM386 audio amplifier. Its
October 1994 39
PARTS LIST
The ISD1416 sound recorder IC is mounted in an IC socket while the two
remaining ICs are soldered directly to the PC board. Take care to ensure that the
two switches are oriented correctly (ie, flat side to the right).
1 PC board, code 01109941,
102 x 58mm
1 plastic zippy case, 130 x 68 x
41mm
1 front-panel label
1 green snap action momentary
switch (S1)
1 red snap action momentary
switch (S2)
1 8-ohm 1W loudspeaker
1 electret microphone insert
1 28-pin machined IC socket
1 10kΩ 5mm trimpot (VR1)
1 5-pin 0.1-inch header
13 PC stakes
4 19mm spacers
4 3 x 30mm machine screws
plus nuts & washers
Semiconductors
1 NE555 timer (IC1)
1 ISD1416 16-second sound
recorder (IC2)
1 LM386 low-power audio
amplifier (IC3)
1 78L05 5V 100mA regulator
(REG1)
1 7809 9V regulator (REG2)
1 BC548 NPN transistor (Q1)
2 1N4004 silicon diodes (D1,D2)
1 5mm red LED (LED1)
Fig.4: this is the full size etching pattern for the PC board.
output appears at pin 5 and drives an
8-ohm loudspeaker via a 100µF ca
pacitor. Trimpot VR1 functions as the
volume control, while a Zobel network
consisting of a 10Ω resistor and series
0.1µF capacitor is connected across the
output of IC3 (pin 5 & GND) to ensure
stability.
Power for IC3 is derived from the
headlight switch via reverse polarity
protection diode D2 and 9V regulator
REG2. Regulator REG1 provides a 5V
rail to power the rest of the circuit.
Recording
The recording mode is activated by
pressing switch S2 (RECORD). This
pulls the REC line (pin 27) of IC2
low, which then pulls the RECLED
line (pin 25) low via internal logic
circuitry. When this happens, the
electret microphone turns on and
feeds the incoming audio signal into
pin 18 for storage in the EEPROM. At
40 Silicon Chip
the same time, LED 1 (RECORD) turns
on to indicate that the unit is in the
recording mode.
Recording either ceases after 16
seconds or when the RECORD button is released, which ever comes
first. In either case, pin 25 goes high
again and LED 1 and the microphone
turn off.
Capacitors
3 100µF 16VW electrolytic
1 22µF 25VW electrolytic
2 10µF 16VW electrolytic
1 4.7µF 25VW electrolytic
2 1µF 63VW electrolytic
2 0.22µF 63VW MKT polyester
4 0.1µF 63VW MKT polyester
Resistors (0.25W, 1%)
1 1MΩ
2 10Ω
1 470kΩ
4 1kΩ
4 100kΩ
1 4.7kΩ
2 10kΩ
Construction
Most of the parts for the Talking
Headlight Reminder are installed on a
PC board coded 01109941. Fig.3 shows
the parts layout.
Begin the assembly by installing
2-pin and 3-pin headers at the LED
and microphone wiring points respectively, then install PC stakes at
the switch mounting positions and at
all remaining external wiring points.
This done, solder in the wire links,
followed by the resistors, capacitors,
diodes and transistors.
Make sure that all polarised parts
are correctly oriented and note that
the 22µF capacitor near IC1 should
be mounted with its body flat against
the PC board – see photo. Table 1 lists
the resistor colour codes but it’s also a
good idea to check them on a digital
multimeter as some of the colours can
be difficult to decipher.
The ISD1416 (IC3) is installed using
a 28-pin machined IC socket. This is
done because the chip is reasonably
expensive to replace. The other ICs
on pins 4 & 8 of IC1 and pins
24 & 28 of IC2. If these checks
prove OK, check that Q1’s collector switches low for about
30 seconds when the PLAY
button is pressed. If it doesn’t,
check the circuit around IC1
and Q1.
Assuming that everything
works correctly, the unit can
now be installed in your car.
There are just three wiring connections to be made: (1) to the
negative side of the headlight
switch; (2) to chassis; and (3) to
the negative side of the ignition
switch. In addition, you will
have to run two leads to the
external speaker. These should
be passed through a grommeted hole
in the side of the case.
Perhaps the easiest way of connecting to the headlight switch circuit is
to simply tap into the positive lead to
the tail lights. This has two advantages: (1) ease of access (gaining access
to the back of the headlights switch
is usually quite difficult); and (2) the
tail lights come on in both the parking
lights and headlights switch positions,
so you don’t have to find the parking
lights terminal. Note: the unit should
warn if either the parking lights or the
headlights are left on.
Use automotive connectors to interface to the car’s wiring and make
sure that all wiring is installed in a
professional manner. The last thing
you want is a fault in your car’s lighting
system due to sloppy wiring.
Finally, check that the unit operates
correctly in the car and adjust VR1
to give the desired volume level. We
recommend that you keep the volume
setting low, to minimise any annoyance on those occasions when you do
SC
trigger the unit.
TALKING HEADLIGHT
REMINDER
MIC
+
+
PLAY
REC
REC ON
+
+
Fig.5: this full size artwork can be used as a drilling template for the front panel.
can then be installed in the normal
manner, followed by the two 3-terminal regulators.
The two pushbutton switches
can now be mounted in position by
soldering their leads to the tops of
the PC stakes. Use a green switch for
S1 (PLAY) and a red switch for S2
(RECORD). Make sure that the two
switches are correctly oriented; ie, the
flat side of each switch must go to the
right – see Fig.2.
The microphone and LED 1 are
connected to their respective pin
headers on the board using light-duty
hook-up wire. Take care to ensure that
these devices are connected with the
correct polarity.
Final assembly
The PC board is installed on the
lid of a small zippy case (130 x 68
x 41mm) and is mounted on 19mm
spacers so that the snap action
switches just protrude through the
front panel.
The first step is to attach the front
panel and then use this as a drilling
template for the four mounting holes.
Holes will also have to be drilled for
the two pushbutton switches, the microphone and the LED. Note that the
larger holes should be made by first
drilling small pilot holes and then
carefully enlarging them to the correct
size using a tapered reamer.
Both the LED and the microphone
should be a push fit into their respective holes. They can be finally secured
in position using a small dab of epoxy
adhesive. This done, the board can be
mounted in position and secured using
machine screws and nuts.
Test & installation
To test the unit, connect a 12V power
supply to the V+ and chassis terminals,
then hold down the RECORD button
while you speak into the microphone.
The message should now replay when
you press the PLAY button and should
continually repeat for a period of 30
seconds.
If it doesn’t work, first check for
+5V at the output of REG1 and on pin
6 of IC3. Check also that +5V appears
TABLE 1: RESISTOR COLOUR CODES
Value
4-Band Code (1%)
5-Band Code (1%)
❏ 1
1MΩ
brown black green brown
brown black black yellow brown
❏ 1
470kΩ
yellow violet yellow brown
yellow violet black orange brown
❏ 4
100kΩ
brown black yellow brown
brown black black orange brown
❏ 2
10kΩ
brown black orange brown
brown black black red brown
❏ 1
4.7kΩ
yellow violet red brown
yellow violet black brown brown
❏ 4
1kΩ
brown black red brown
brown black black brown brown
❏ 2
10Ω
brown black black brown
brown black black gold brown
❏
No.
October 1994 41
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