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Hnr|0Fctsfr$r ftdmomr
- _
ALARM (E/P)
OVER-TEMPERATURE
Thiscircuit produce
will beeps a piezoelectric
intermittent by when
transducer
the temperature overa
rises preadjusted in
Youcan usethiscircuit
value.
greenhouses, etc.The
heaters, is
Sensor a common diode an NTC
silicon but
canalsobe usedif youchange some components'values.
Exchanging to
positions R1andPl withDl willcause device operate
of the
alarm.
as an under-temperature
Theintermittentsignal generated twooscillators. (pins1,2and3)
is by lGla
is aninverter controls b and
that lCl lOlc (oscillators). c (pins 9 and10)
lOl 8,
is a very-low-frequencyoscillator provides modulation for the
that the rate
second oscillator. second
The (pins5,6 and
oscillator 4) hasits frequency
determined R2andC1.The
by produced audio by
tonecanbealtered adjust-
ingbothC1andR2within large
a range values.
of
Power comes power
froma 3- to lS-volt supply" portable a small
For use 9-
voltbattery recommended.
is drainis verylow,about mAwhen
Current 0.5
thetoneis otf.When toneis on,current
the drain rises about mA.
to 5
A schematic the Over-Temperature is shownin Figurc 1. lOl, a
of Alarm
40ggB, twogatesoperating oscillators twoas butfer'inverters.
has as and
Componentsplacement a homemade
on boardis shown
printed-circuit in
Figure2.You made
can PC
using single-sided board.
yourprototype a
Position thepolarized
of especially
components, diode (used sensor),
D1 as
should observed. sensor be
be This can by
placed fromthedevice using
far
common wiring. musttakesomecareto avoid
You humidity water
or falling
ontothesensor,which cause
will adversely the
atfect alarm operation.
BZ is a piezoelectric (Radio
transducer 27g-O7g equivalent) a
Shack or or
crystalearpiece.
Operation adjusted P1.Setthispotentiometergetsound the de-
is by to at
siiedtemperature. get a moreprecise
To you
adiustment can replacethe
common potentiometer.
potentiometer a multi-turn
trimmer by
ltf
Pfrfrcl25 M-Iomnnurulhm
vcc
+3Vto +15V
P1
10M
R1
100K
Figure 1
0V +Vcc +
Figure2
Getthesensor your
between fingers seehowit works:
to when tempera-
the
turerisessomedegrees circuit produce serieof beeps.
the will a the
lsolate
sensor, aftersome
and secondssound will
emission stop.
ftnPniloctsfi$e mdlffibl
PartsList - Over-Temperature
Alarm
lC1 - 4093CMOSintegrated
circuit
D1 - 1N914 1N4148
or purpose
general diode
silicon
;
BZ - Piezoelectric or earphone
transducer crystal j
(Radio
Shack 273-073 equivalent)
or I
I
!
R1 - 100,000 resistor
ohm,1l4W,5olo
R2 - 33,000 resistor
ohm,114W,5%
R3 - 2,200,000 114W,5%
ohm, resistor
Pl - 10,000,000 trimmer
ohm potentiomer
Cl - 0.047 metal or ceramic
uF film capacitor
C2 - 0.47uF metal or ceramic
film capacitor
Cg - 100uF,16WVDC capacitor
electrolytic
ldeasto Explore
To learnmore performance:
about circuit to getbetter
the or
tonepitchor bothR3 andG2to
o AlterbothR2 andC1 to change
rate.
altermodulation
o Replace witha 10,000 100,000 NTC, witha2,200
Dl to ohm Rl
ohmresistor, P1witha 100,000 1,000,000 potentiometer,
and to ohm
to geta newkindof sensor.
o Tryto adda power{ul
output stage
audio such
using transistor, as
a
a 8D135 a smallloudspeaker. other
and See projects thisbookfor
in
the
about configuration.
suggestions
r50
Pnfocfl ow-lcmrunnnilnm
25
Scienceprojects
and otherapplications:
o Chemical processesthat involveheatchangescan be controlled
usingthis alarm.The sensorshouldbe protectedagainstmoisture
involving
and waterin experiments liquids.
o Replace by an LDRor photodiode. circuitwill operate a
D1 The as
lightalarmor darkalarm,depending upon sensorposition. Withan
LDRit wouldbe betterto replace witha 1,000,000
P1 ohm potentiom-
eter and R1 with a 10,000 Lensesplacedin frontof the
ohm resistor.
LDRor phototransistor be usedto increase
can sensitivity.
o The circuitcan alsooperate a water-level
as alarmby usinga two-
wire sensorto replaceDl. The sensoris madewith two barewires.
The wires are separated a distanceof about2 or 3 inches.
by The
watercompletes circuitwhilethe wiresare immersed.
the Whenthe
waterlevelfallsbelowthe wires,the circuitis openedandthe alarmis
triggered.
. o Temperature greenhouses,
in animalpens,incubators aquari-
and
ums can be monitored And if workingwith an LDR
usingthis device.
as the sensor,
experiments lightcan be conducted.
involving
tut
