13-05-2011, 03:34 PM
If your PC overheats, it coulddamage its expensive components.Here’s a circuit that warns you ofyour PC getting heated.Today’s computers contain mostof the circuitry on just a few chipsand reduced power consumption isa byproduct of this LSI and VSLIapproach. Some PCs still havepower supplies that are capable ofsupplying around 200W, but fewPCs actually consume power to thisextent.On the other hand, apart fromsome portable and small desktop computersthat use the latest micro-powercomponents, most PCs still consumesignificant amount of power and generatecertain amount of heat.The temperature inside the averagePC starts to rise well above theambient temperature soon after it isswitched on. Some of the larger integratedcircuits become quite hot andif the temperature inside the PC risestoo high, these devices may not beable to dissipate heat fast enough.This, in turn, could lead to failure ofdevices and eventually of the PC.Various means to combat overheatingare available, ranging from simpletemperature alarms to devices liketemperature-activated fans to keep themicroprocessor cool.Here is a temperature alarm thatactivates an audio ‘beeper’ if the temperatureinside the PC exceeds a presetthreshold. This temperature is useradjustableand can be anywhere between0°C and 100°C.The unit is in the form of asmall PC expansion card, which yousimply need to plug into any availableslot of the host PC. It is poweredfrom the PC and consumes only about12 mA.The sensor (LM35) used here providesa substantial amount of on-chipsignal conditioning, including amplification,level shifting and phase inversion.As a result, it provides an outputof 10 mV per degree centigraderise in temperature. It caters to a temperaturemeasurement range of 0°C to100°C, which corresponds to 0V to 1Vof voltage.The voltage-detector stage comparesthe output voltage of the temperaturesensor with the preset referencevoltage. The output of the comparatorgoes high if the output potentialfrom the sensor exceeds thereference voltage. When this happens,the voltage comparator enables a lowfrequencyoscillator, which, in turn,activates the audio oscillator. The outputof the audio oscillator is connectedto a loudspeaker (LS1), which soundsa simple ‘beep-beep’ alarm. The referencevoltage determines the temperatureat which the alarm is activated.Fig. 1 shows the circuit of the PCtemperature alarm and Fig. 2 showsthe pin configuration of sensor LM35.IC LM35 (IC1) is an easy-to-usetemperature sensor. It is basically athree-terminal device (two supplyleads plus the output) that operates
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