HIGH TEMPERATURE INDICATOR CIRCUIT

In some areas there is a need of
temperature detectors which help
them to detect temperature and
indicate them whether the
temperature is low or not.
Below shown circuit is the simple high
temperature indicator circuit. It will
not show the current temperature
but if it exceeds some threshold
temperature it will detect and indicate.
You can use this circuit anywhere you
needed.

The components needed for the
circuit are:
3 Resistors
1 Temperature dependent resistor
5v battery
Two 1n4007 diodes
One Op-Amp
One LED
And the circuit working is actually very
simple, the Op-amp is connected as
Non-inverting comparator. And a
bridge circuit is made with the
resistors and a Temperature
Dependent Resistor. From above
circuit R1, R2 and R3 are normal
resistors but RT is Temperature
Dependent Resistor.
The bridge resistance and RT are
selected in such a way that as long as
temperature is less than threshold
value, the bridge is unbalanced by
making Voltage at B more than
voltage at A . Hence Vo = -Vsat and
LED is reverse biased and remains
OFF. When temperature becomes
more than threshold then Voltage at B
becomes less that Voltage at A hence
it drives Vo = +Vsat. Due to this, LED
glows and gives high temperature
indication.

Temperature and Humidity Meter

Digital thermometer or thermostat
projects have been around for many
years. This project, in order to be
appealing in such explored subject,
incorporates a number of interesting
features, never put together in one
single circuit and, some of them, only
available on professional equipment.
The first characteristic that is worth
noting is that the circuit, from now on
called Meter, also measures relative
humidity. As temperature and relative
humidity Measurements are taken,
the Meter keeps record of observed
maximum and minimum levels. Each
reading is also compared to user set
maximum and minimum limits which,
if exceeded, will trigger outputs that
may be used to drive external circuits.
Temperature measurements are
made in either Celsius or Fahrenheit
degrees. A digital clock keeps track of
time, day, weekday, month and year
which is an important information
when the Meter is collecting and
storing measurements in its
microcontroller EEPROM
The temperature and humidity meter
entire setup is configured and
developed using Microchip 18F 4525
controller with assembly
programming firmware support. This
project is having multiple Menu
configuration setup with Respect to
S1,S2,S3 switches, along with that
Analog signal configuration and low
battery detection and update
temperature relative humidity stored
in inbuilt EEPROM of PIC18F4525
controller and we can record time
intravel between minimum and
maximum measurement of
temperature and humidity. Visual
Basic is front end tool is used for user
friendly configuration to set maximum
and minimum temperature and
relative humidity and it’s having more
user friendly selected option like
temperature measurements are made
in either Celsius or Fahrenheit
degrees, program memory read
configuration and meter
configuration.
The Entire setup is design with
appropriate schematic, visual basic
frontend and various hardware
selections to design this meter.
Source: Elektro Projects