Boss Audio Systems BV8.5GA User Manual download pdf (Page 52)

Build

VERBAT

/LE

DIGITAL

LED

THERMOMETER

Low -cost, accurate

device

can be

used

indoor /outdoor

thermometer

heater /cooler

thermostat

temperature

alarm

fishing thermometer

THE

digital

thermometer

de-

scribed

here

was

designed for

low

cost

and simplicity,

well

ac-

curacy. If you

check the

semiconduc-

tor

sales ads in this magazine

and use

conventional

thermistor,

you

can

build the

thermometer

for

about $15.

you decide

to use

a precision thermis-

tor,

the

cost will

be about $20.

Since

the

thermometer

operates

from

-volt line,

it can

be used in

a car,

boat, or camper. With

line-

powered

5 -volt

supply,

can be

used

the

home.

possible to

use two

switchable

thermistors

to check temperature

differentials

-such

as between the

outside and inside,

or between two

rooms.

long lead

used between

the thermistor

and the

electronic cir-

cuit, the project

can be used

as a

fish-

ing thermometer.

THOMAS R. FOX

How It Works.

The

frequency

the

CMOS

multivibrator

(Fig.

depends

the resistance

thermistor

TDR1,

which is determined by the

ambient

temperature. Thus, if the temperature

goes

up. the

frequency

of the

multivi-

brator

goes

up, and

vice versa. Trim-

mer potentiometer R23 is used to

ad-

just the

linearity.

The

two

-transistor

multivibrator (Q1

and Q2) automatically

resets the two

POPULAR ELECTRONICS

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Boss Audio Systems BV8.5GA User Manual Page 52

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