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DIAL
ALARM-1
CONSTRUCTION
Page 2.
BUILDING THE PROJECT
All the components fit on to a PC board labelled Dial Alarm-1. The placement of
each component is clearly shown by the overlay on the board and
the only components requiring careful attention are the opto-coupler and bridge.
The opto-coupler has line running down one side of the chip and when viewed from the top, with the line towards you, pin one at the left.
The chip may also have a dot or dimple indicating pin 1 and/or a cut-out at one end.
The bridge has positive (+) and negative (-) marked on the top of the chip as well as AC inputs indicated by squiggle lines.
Don't get the BC 557 confused with the BC 547 or BC 338 transistor. They all
look the same and have the same pin-outs, but their function is different. The
outside case of the electret microphone must go to the negative rail. The microphone
can be fitted to a short length of twin lead or fine screened microphones lead
(as supplied in the kit) so it can be positioned near
the audio you wish to detect.
Solder the 8-pin IC socket for the microcontroller to the board so that the cut-out, covers the cut-out on the board. This
way the chip will always be fitted around the correct way.
The 4-core telephone cable comes with 4-pin plugs crimped on each end. A
4-pin modular telephone socket is soldered to the board.
Click on the 5 red
dots to see the circuit
working
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Dial
Alarm-1
PARTS
LIST
Cost xx$45.75
plus
$2.20 postage
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3
- 100R 1/4 watt
1 - 470R
"
1 -
560R "
1 -
1k
"
1 - 4k7
"
4 - 10k
"
1 - 22k
"
1 -
47k
"
3 -
100k "
1 -
220k "
2 -
1M
"
1 -
2M2
"
2 - 18p ceramics
1 - 22n ceramic
1 - 33n ceramic
1 - 47n ceramic
2 - 100n ceramics
2 - 1u 25vw electrolytics
1 - 4u7 25vw electrolytic
1 - 47u 25vw electrolytic
3 - 100u 16vw electrolytics
1 - 4MHz crystal
1 - electret microphone insert
2 - BC 547 transistor or similar
2 - BC 557 transistor or similar
1 - BC 338 transistor or similar
1 - BD 679 transistor
1 - 1N4148 signal diode
1 - DF 04 bridge
1 - 4N25 opto-coupler
1 - 10mH choke
1 - 6 pin IC socket
1 - 8 pin IC socket
1 - 4-cell AA battery holder
4 - AA cells
1 - mercury tilt switch
3m - 4-core telephone cable with plugs
crimped on the ends
2m - fine screened microphone lead
3m - very fine solder
1 - PIC12c508A (blank)
1 - Dial Alarm-1 PC board |
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PC Board only
xx$4.50 plus
$2.20 postage
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Buy
a kit
TESTING THE PROJECT
The project is tested either on a 50v line or the Test Circuit shown in the
diagram below. The supply is three 9v batteries.
It
does not matter which way around the phone or Dial Alarm-1is connected as both have a diode bridge to accept either polarity.
When the mercury switch is activated, the alarm sends a Hee Haw tone down the line and this is detected by listening to
the line via another telephone connected in series with the Dial Alarm-1 project,
as shown in the diagram above.
The audio from the room is then sent down the line. After 15 seconds
the Hee Haw is produced again over the audio and this is
repeated at a further 15 seconds. The project then closes down, waits a few seconds then dials the second number and repeats the operation.
The two numbers are dialled again and the Alarm closes down.
You can repeat the sequence in the Test Circuit and during the listening period, push any of the buttons on the phone to send a DTMF tone down the line.
The project will close down. The actual closing-down of the circuit takes a
while as the electrolytics in the shut-down circuit have to "bleed" though
high value resistors. The micro stays in a holding loop during this process, with a CLRWDT instruction.
If the input of the alarm is connected to a reed or mercury switch on a door, the door will have to be closed
again to reset the tilt circuit.
IF THE
PROJECT DOESN'T WORK
If the project doesn't work you will have to go to one of the following sections:
1. The turn-on circuit.
To test the turn-on circuit, short between collector and emitter of the BC 557 transistor. The project will come on and operate.
Put a 10k resistor on jumper leads and connect it between the base of the BC 557 and ground. This will turn the transistor on. If not,
the transistor is faulty or it is a BC547! If this works, take the jumper from the join of the two electrolytics
and ground. This will also turn the transistor on. If not, the 100k
may be open between the join of the electro's and the base of the transistor or the top 100u may be very leaky and have a very low resistance.
Finally place a jumper lead across the tilt or reed switch. If this doesn't work, the lower 100u may be open circuit. If it does work the
tilt or reed switch may be faulty.
2. The tone detector amplifier
The tone detector transistor is normally gated off and the collector will be at
rail voltage. At the same time, the 4u7 electrolytic is fully charged via
a 100k resistor. When a signal is detected, the transistor turns on and
discharges the electrolytic. This is very easy to monitor via a multimeter
on line GP3.
3.
The DTMF Section.
The quickest way to determine if this section is working is to pick up the phone and activate the
alarm, by tilting the mercury switch.
You will hear the DTMF tone being sent down the line.
If these tones are not heard, you can produce a constant dual tone for say "0" by inserting the following instructions into the program.
Make sure they are removed after the testing is complete.
At the end of the SetUp routine insert:
MOVLW 057h
MOVWF 16h
MOVLW 03Dh
MOVWF 14h
GOTO DTMF1
The third last instruction in DTMF1 must be delineated i.e: ;DECFSZ 11h,1
Placing a piezo between pin 6 and ground will allow you to hear one of the tones and between pin
7 and ground, the other tone.
The tones will be produced continuously and you can view them on a CRO and observe their waveshape entering the phone line. To view one tone at a time, the micro can be put into an old 8-pin
socket, with one of the output pins missing - this way none of the components have to be removed from the board.
4.
The Opto-Coupler
To see if the opto-coupler is "turning on," short between pins 4 and 5 with a jumper lead.
This will turn on the BD 679 transistor. If you also turn on the TURN-ON circuit with
a jumper lead between the join of the two 100u electrolytics and
ground, you will be able to hear the room-audio, through the telephone. The opto-coupler
is turned on by activating the LED between pins 1 and 2. The illumination
of the LED turns on a photo-sensitive transistor between pins 5 and 4. The
LED only needs a few milliamp to turn on the transistor sufficiently to
drive the BD 679 into saturation, as it is a super-alpha device.
The micro takes pin 5 low to turn on both the "turn-on" circuit and
LED in the opto-coupler, but you cannot do this manually as you may damage the output line of the micro.
When the project is operating you can check the voltage across the 560R resistor. This does not tell you very much except that if it
is about 3v, the LED inside the opto-coupler and micro are (maybe)
operating correctly.
Check the voltage across the pins 4 and 5 of the opto-coupler. It should be about
2v. If it is higher than 5v, the opto-coupler is not
being turned on enough. It could be insufficient current through the LED or a faulty opto-coupler.
5.
The High-Gain Audio Amplifier
The audio amplifier consists of two stages. The pre-amplifier (the low-signal stage) and the buffer stage (output stage).
The pre-amplifier section consists of a standard common-emitter amplifier with AC coupling (capacitor coupling) to the microphone. It
may look unusual because it is a PNP stage. This has been done so that one of
the lines from the micro can be used to gate the audio amplifier OFF.
You will need either a CRO or an audio tracer to listen to or observe the signal from the microphone
through to the output transistor.
Our circuit had a gain of 50, with a 20mV signal (whistle) from the microphone producing 1,000mV (1v) signal into the base of the buffer
stage, (output stage).
The output transistor amplifies this to produce a signal of about 3v
on the phone line. You will need a CRO to view the waveforms if you think the audio amplifier
is not operating correctly. A dual-trace CRO is best so you can observe the input and output of a
particular stage at the same time.
This completes the coverage of all the individual building blocks in the circuit.
If a fault still persists, the best way to tackle the problem is to get another electronics person to check the board. It may be a simple
mistake such as swapping two components, a solder bridge or dry joint.
As a last resort, you can build another kit and with the second project working, compare the two.
Go to: Page
3.
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