PC Heat Monitor

The PC processor generates very high temperature during its operation which is dissipated by the large heat sink placed above the processor. If the heat sink assembly is not tight with the processor or the cooling fan is not working, PC enters into the Thermal shutdown mode and will not boot up. If the PC is not entering into thermal shutdown, the high temperature can destroy the processor. This simple circuit can be placed inside the PC to monitor the temperature near the processor. It gives warning beeps when the temperature near the heat sink increases abnormally. This helps to shutdown the PC immediately before it enters into Thermal shutdown.

 

The circuit uses a Piezo element (one used in Buzzer) as the heat sensor. The piezo crystals reorient when subjected to heat or mechanical stress and generates about one volt through the Direct piezoelectric property. IC1 is designed as a voltage sensor with both the inputs tied through the capacitor C1.The non inverting input is connected to the ground through R1 to keep the output low in the standby state. The inputs of IC1 are very sensitive and even a minute change in voltage level will change the output state.

In the standby mode, both the inputs of IC1 are balanced so that output remains low. When the Piezo element accepts heat, it generates a minute voltage which will upset the input balance and output swings high. This triggers LED and Buzzer. Capacitor C2 gives a short lag before the buzzer beeps to avoid false triggering. Warning beep continues till the piezo element cools.

Note: Enclose the circuit inside the PC with the piezo element close to the heat sink of the processor. Adjust the distance between the piezo element and heat sink so as to keep the circuit standby in the normal condition. The piezo element can sense a 10 degree rise in temperature from a distance of 5 cms. Power to the circuit can be tapped from the 12 volt line of SMPS.

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PC Driven LED Display Wiring diagram Schematic

Here is a schema to generate sequentially running light effects using a simple program written in C. The output of the program is taken from the LPT port of a PC and then fed to the interfacing schema for the LED display. The outputs of the interfacing schema are decoded, inverted, and then connected to LEDs through optocouplers.

 Fig. 1: Interfacing schema for PC-driven LED display

The interfacing schema along with the 25-pin parallel port is shown in Fig. 1. IC1 (74LS138) is a high-speed 1-of-8 decoder/demultiplexer. In the schema, only five outputs (pins 10 through 14) of IC1 are used. These outputs are inverted using  NOT gate IC2 (7404). Optocouplers IC3 through IC7 (MCT2E) are used to prevent the schema from damage in the event of short schema in the load.  Thus the loads comprising LED blocks LB1 through LB5 are isolated from the interfacing schema including the PC. Each LED block contains a number of LEDs connected in series.

The LEDs can be arranged, for instance, to display a sequential running light and fountain pot as shown in Figs 2 and 3. The colour of LED blocks can be green and red alternately.

Fig. 2: LED block arrangement for sequentially running light   

 Fig. 3: LED block arrangement for fountain pot

The program can be compiled and run through Turbo C compiler. In the program, the function outport(p,x) is used, where ‘p’ is the address of the controller port and ‘x’ is the value sent to it. Here, controller port  LPT1 is used, whose base address is 378H. If LPT2 is to be used, the base address must be 278H. When the delay time delay() is increased, the running speed of LEDs decreases and vice versa.

In the schema, 100-ohm fixed resistors R6 through R10 can be replaced with 100-ohm or 200-ohm presets for decreasing and increasing the intensity of LEDs.

The program for LED display is as follows:

This schema costs around Rs 100.

Sourced By: EFY Electronics Author:  R. Karthick

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