Introduction
If your PC overheats,
it could damage its expensive components. Here’s a circuit that warns you of
your PC getting heated.
The temperature inside the average PC starts to rise well above the ambient
temperature soon after it is switched on. Some of the larger integrated
circuits become quite hot and if the temperature inside the PC rises too high,
these devices may not be able to dissipate heat fast enough. This, in turn,
could lead to failure of devices and eventually of the PC.
Various means to combat overheating are available, ranging from simple temperature alarms to devices like temperature-activated fans to keep the microprocessor cool.
Various means to combat overheating are available, ranging from simple temperature alarms to devices like temperature-activated fans to keep the microprocessor cool.
Here
is a temperature alarm that activates an audio 'beeper' if the temperature
inside the PC exceeds a preset threshold. This temperature is user-adjustable
and can be any where between 0oC and 100oC.
The unit is in the form of a small PC expansion card, which you simply need to plug into any available slot of the host PC. It is powered from the PC and consumes only about 12 mA.
The unit is in the form of a small PC expansion card, which you simply need to plug into any available slot of the host PC. It is powered from the PC and consumes only about 12 mA.
The sensor (LM35) used here provides a substantial amount of on-chip signal conditioning, including amplification, level shifting and phase inversion. As a result, it provides an output of 10 mV per degree centigrade rise in temperature. It caters to a temperature measurement range of 0°C to 100oC, which corresponds to 0V to 1V of voltage.
The
voltage-detector stage compares the output voltage of the temperature sensor
with the preset reference voltage. The output of the comparator goes high if
the output potential from the sensor exceeds the reference voltage. When this
happens, the voltage comparator enables a low-frequency oscillator, which, in
turn, activates the audio oscillator. The output of the audio oscillator is
connected to a loudspeaker (LS1), which sounds a simple ‘beep-beep’ alarm. The
reference voltage determines the temperature at which the alarm is activated.
Circuit Diagram
Working
Above figure shows the
circuit of the PC temperature alarm and the below figure shows the pin configuration of
sensor LM35. IC LM35 (IC1) is an easy-to-use temperature sensor. It is
basically a three-terminal device (two supply leads plus the output) that
operates over a wide supply range of 4 to 20V. It consumes only 56 µA at 5V and
generates insignificant heat. IC2 is an operational amplifier used here as a
voltage comparator. VR1 provides a reference voltage that can be set anywhere
from 0V to approximately 1V, which matches the output voltage range of IC1.
This reference voltage is applied to the inverting input of IC2 and the output
of IC1 is coupled to the non-inverting input. Consequently, the output of IC2
is low if the output of IC1 is below the reference voltage, or high if the
output of IC1 exceeds the reference voltage.
The
low-frequency oscillator IC3 is a standard 555 astable multivibrator
circuit. It is gated via the reset input at pin 4, which holds output pin 3 low
when IC3 is gated 'off' (when the output of IC2 is low). This prevents IC4 from
oscillating. IC4 is another 555 astable multivibrator circuit, gated via its
reset input. It has an operating frequency of approximately 2.5 kHz.
When
IC3 is activated, its output provides a square wave of 1 Hz. This is used
to trigger IC4, which gives an audio output of 2.5 kHz in bursts. It is
connected to loudspeaker LS1 to generate alarm. The alarm circuit can be fitted
into any spare expansion slot of the PC, but be careful to fit it the right way
round. Before setting VR1 to a suitable threshold temperature, decide what that
temperature should be. The technical specification in your computer's manual
might be of help here. If we assume that the room temperature will not normally
exceed 25oC, the temperature of the interior of the computer
would be up to 35oC. Unless you have good reason to use a different
threshold temperature, VR1 should be set for a wiper potential of 350 mV.
Trial-and-error method can be used in the absence of test equipment to enable
VR1, but it would be a bit time-consuming. There is a slight complication in
that the computer's outer casing must be at least partially removed to provide
access to VR1. Once VR1 has been adjusted, the outer casing must be put back
into place so that the interior of the computer can warm up in the normal way.
You must therefore allow time for the temperature inside the computer to rise
back to its normal operating level each time VR1 is readjusted.
Datasheets
-Ankur Pipara
+91-77 37 44 84 68
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