Processor Fan Control

Fans in PCs can be objectionably loud. In many cases, the amount of noise produced by the fan can be considerably reduced by lowering its speed. Although this will decrease the amount of cooling, this need not be a problem as long as you don’t go overboard with slowing down the fan. Particularly with older-model processors, which consume quite a bit less power than the latest models, this trick can be used without any problems. This circuit is anyhow intended to be used with relatively old PCs, since more recent models generally have a fan control circuit already integrated into the motherboard. These controllers ensure that the amount of cooling is increased if the processor becomes too warm and decreased if the processor temperature is relatively low.

The circuit described here consists of only a handful of components, which you will probably already have in a drawer some-where. Transistors T1 and T2 are driven into conduction by the base current flowing to the fan via P1 and D1. There will always be a current flowing through R1, and it will be approximately 120 times as large as the current through R2. R3 has been added to prevent the base current of T2 from becoming too large when P2 is set to its minimum resistance. D1 ensures that even at this extreme setting, the voltage on the base-emitter junction of T3 will still be large enough to allow it to conduct.

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DS1669 Digital Volume Control circuits

This circuit is used for replacing your manual volume control in a stereo amplifier. In this circuit, push-to-on switch S1 controls the forward (volume increase) operation of both channels while a similar switch S2 controls reverse (volume decrease) operation of both channels.

A readily available IC from Dallas semiconductor, DS1669 is used here.

FEATURES:

Replaces mechanical variable resistors
Electronic interface provided for digital as well as manual control
Wide differential input voltage range between 4.5 and 8 volts
Wiper position is maintained in the absence of power
Low-cost alternative to mechanical controls
Applications include volume, tone, contrast,brightness, and dimmer control

The circuit is extremely simple and compact requiring very few external components.

The power supply can vary from 4.5V to 8V. (DS1669 Digital Volume Control circuits.)

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Simple Tone Control Circuit with LM301A

This circuit and a simple collection circuit Tone Control. This circuit tone control with surgical Amp LM301A. The JFET 2N3684 feature gives a high input impedance and low noise for UN buffer zone opinion operational amplifier operated EQ sort. Could you see intimately of the circuit following hence as under.

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Battery Charger Control Circuit

Battery charger control circuit is very useful now-a-days. You need not follow on battery charging or disconnect from ac power for avoiding over charge. This circuit is used to charge battery when the battery voltage drops
below the minimum voltage that you want to connect it to a charger.
When the battery voltage reaches the maximum voltage you want the
charger to be connected.

This
circuit is shown in figure. Let your battery voltage is 15 volt. When
Ei drops below 10.5 V, V0 goes negative, releasing the relay to its
normally closed position. The relay’s normally closed (NC) contacts connect the charger to battery Ei. Diode D1 protects the transistor against excessive reverse bias
when V0 = -Vsat. When the battery charges to 13.5 V, V0 switches to
disconnect the charger. Diode D2 protects both op-amp and resistor
against transients developed by the relay’s collapsing magnetic field.

Suppose that the application requires an inverting voltage level detector with hysteresis.
That is V0 must go low when Ei goes above Vut and V0 must go high when
Ei drops below Vlt. For this application, do not change the circuit or
design procedure for the non-inverting voltage level detectors, simply
add an inverting amplifier, or inverting comparator, to the output Vo.

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