Cooler malfunction indicator. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Computers
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The device is designed to give an audible signal when the fan that cools the PC CPU (i.e. the cooler) stops. The signaling device is included in the break of the cooler's power cable, the dimensions of the printed circuit board are 40x32.5 mm (fits in a matchbox). The schematic diagram of the signaling device is shown in fig. one.
The operation of the device is based on the shape of the current consumed by the cooler (Fig. 2). A voltage proportional to the current through the cooler is removed from the resistor R1, with a pulse amplitude of about 2V. Filter C1R2 suppresses the DC component of the signal so that in the absence of pulses, the transistor VT1 is completely closed. Each current pulse (one turn of the cooler) opens transistor VT1 for a short time, discharging capacitor C2. After the end of the pulse, the transistor closes, the capacitor C2 begins to gradually charge through R4, but during normal operation of the cooler, by the time the next pulse arrives, it has time to charge slightly, a low level is constantly present at input 9 DD1. When the cooler breaks, jams or closes, the current pulses stop coming to the input of the signaling device, the transistor VT1 is constantly closed, and the capacitor C2 is charged (the resistance of the resistor R4 is selected so that the steady voltage at C2 is confidently recognized by the microcircuit as a high level). A high level at input 9 DD1 allows the operation of the generator, assembled on the valves DD1.1-DD1.4 and generating an intermittent sound signal. The sound frequency depends on C4 and R6 (the values \u2b\u3bgiven in the diagram correspond to approximately 5 kHz), the sound interruption frequency - using C9 and R10 (according to the scheme 3-4 Hz). As a sound emitter, you can use a piezoelectric capsule (similar to those used in electronic alarm clocks and telephones). The version of the printed circuit board of the signaling device and the wiring diagram are shown in fig. XNUMX and XNUMX, respectively.
The signaling device is configured in two stages. First, by selecting R1 and C1, it is necessary to achieve a stable opening of the transistor VT1 with positive cooler current pulses. Then, by selecting R4 and C2, the allowable interval between pulses is set, after which the alarm is activated. It is advisable to monitor the voltage waveform across capacitor C2 using an oscilloscope.
Author: A.Yanovsky; Publication: cxem.net
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