High temperature indicator circuit

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.

If you have any doubts about the above circuit, don’t hesitate to comment.

220 v blinking LED circuit

220V blinking LED circuit

This is a simple blinking led circuit powered from 220V that can be used to mark special places or as voltage indicator. The voltage from the mains charges the capacitor through R1 resistor and D1 diode.

As long as the capacitor’s voltage doesn’t exceeds the diac’s switching voltage the cap is acting as a blocked diode. After reaching the switching voltage the diac is conducting and the cap’s discharging current lights up the LED.

The blinking frequency of the LED depends mostly on the RC time constant (in this case T = 11 seconds). The capacitor’s voltage must be a little bit higher than the diac’s breakover voltage.

220 volts blinking LED schematic

SHUTTER GUARD

This sensitive vibration sensor is
exclusively made for shops to
protect against burglary. It will
detect any mechanical or acoustic vibration
in its vicinity when somebody
tries to break the shutter and immediately

switch on a lamp and sound a
warning alarm. A 15-minute time delay
after switch-on allows sufficient
time for the shop owner to close the
shutter.
The front end of the circuit has a
timer built around the popular binary
counter IC CD4060 (IC1) to provide
15-minute time delay for the remaining
circuitry to turn on. Resistors R3
and R4 and capacitor C2 will make
Q9 output high after 15 minutes. Diode
D1 inhibits the clock input (pin
11) to keep the output high till the
power is switched off. Blinking LED1
indicates the oscillation of IC1.

Radiation sensor

here is the simple tool to check the degree of radiation from an electric or electronic instrument
.The led s in the circuit will give a running light pattern at the momemt the circuit sences electromagnetic
radiation from the device.it can detect the radiation from the computer or telivision from a distance of 2feet or more

pyro electric fire alarm

Here is an ultra-sensitive fire
sensor that exploits the direct
piezoelectric property of an
ordinary piezo element to detect fire.
The lead zirconate titanate crystals in
the piezo element have the property
to deform and generate an electric
potential when heated, thus converting
the piezo element into a heat sensor.
The circuit described here is very
sensitive. It gives a warning alarm if
the room temperature increases more
than 10°C. The entire circuit has two
sections—the sensor and the power
supply section.

protection for your electrical appliances

Here is a very low-cost circuit to
save your electrically operated
appliances, such as TV, tape
recorder, refrigerator, and other
instruments during sudden tripping and
resumption of mains supply. Appliances
like refrigerators and air-conditioners are
more prone to damage due to such
conditions.

power failure alarm

Description
This is a very basic alarm designed to let you know when the electricity supply fails. The
alarm is powered from a battery which uses no current consumption at all in standby, a
battery should therefore last its full shelf life.