circuit coll

Wednesday, December 25, 2013

Two Wire Temperature Sensor

Remote temperature measurements have to be linked by some sort of cable to the relevant test instrument. Normally, this is a three-core cable: one core for the signal and the other two for the supply lines. If the link is required to be a two-core cable, one of the supply lines and the signal line have to be combined. This is possible with, for instance, temperature sensors LM334 and LM335. However, these devices provide an output that is directly proportional to absolute temperature and this is not always a practical proposition.

Circuit diagram :

Two-Wire Temperature Sensor-Circuit Diagram

Two-Wire Temperature Sensor Circuit Diagram

If an output signal that is directly proportional to the celsius temperature scale is desired, the present circuit, which uses a Type LM45 sensor, offers a good solution. The LM45 sensor is powered by an alternating voltage, while its out-put is a direct voltage.

The supply to the sensor is provided by a sine-wave generator, based on A 1 and A 2 (see diagram). The alternating volt-age is applied to the signal line in the two-core cable via coupling capacitor C 6 .

The sensor contains a volt-age-doubling rectifier formed by D 1 -D 2 -C 1 -C 2 . This network converts the applied alternating voltage into a direct voltage. Resistor R 2 isolates the output from the load capacitance, while choke L 1 couples the output signal of the sensor to the signal line in the cable. Choke L 1 and capacitor C 2 protect the output against the alternating voltage present on the line.

At the other end of the link, network R 3 -L 2 -C 4 forms a low-pass section that prevents the alternating supply voltage from combining with the sensor out-put. Capacitor C 5 prevents a direct current through R 3 , since this would attenuate the temper-ature-dependent voltage.

The output load should have a high resistance, some 100 kΩ or even higher. The circuit draws a current of a few mA.

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Wednesday, March 20, 2013

Two Basic Motor Speed Controllers

Here are two simple 12V DC motor speed controllers that can be built for just a few dollars. They exploit the fact that the rotational speed of a DC motor is directly proportional to the mean value of its supply voltage. The first circuit shows how variable voltage speed control can be obtained via a potentiometer (VR1) and compound emitter follower (Q1 & Q2). With this arrangement, the motor’s DC voltage can be varied from 0V to about 12V. This type of circuit gives good speed control and self-regulation at medium to high speeds but very poor low-speed control and slow starts. The second circuit uses a switchmode technique to vary motor speed.

Circuit diagram:

Fig.1: a very simple motor speed controller based on a compound emitter follower (Q1 & Q2).

Here a quad NOR gate (IC1) acts as a 50Hz astable multivibrator that generates a rectangular output. The mark-space ratio of the rectangular waveform is fully variable from 20:1 to 1:20 via potentiometer VR1. The output from the multivibrator drives the base of Q1, which in turn drives Q2 and the motor. The motor’s mean supply voltage (integrated over a 50Hz period) is thus fully variable with VR1 but is applied in the form of high-energy "pulses" with peak values of about 12V.

Circuit diagram:

Fig.2: this slightly more complicated circuit gives better low speed control and higher torque.

This type of circuit gives excellent full-range speed control and gives high motor torque, even at very low speeds. Its degree of speed self-regulation is proportional to the mean value of the applied voltage. Note that for most applications, the power transistor (Q2) in both circuits will need to be mounted on an appropriate heatsink.

Source by : Streampowers

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Wednesday, March 6, 2013

How to Make Any Light a Strobe Light Using Just Two Transistors

If you feel strobe lights very interesting but are disappointed by the fact that these wonderful light effects can be produced only through complex xenon tube then probably you are quite mistaken. It is very much possible to make any light a strobe light if you are equipped with a proper driving circuit capable of handling different lighting devices to generate the desired strobe light effect. The present article shows how a circuit as basic as a multivibrator may be modified in different ways and made compatible with ordinary bulbs, lasers, LEDs to produce spectacular light pulses.

A strobe light may be used for warning, scientific analysis or as an entertainment device, whatever may be the application the effects are simply dazzling. In fact it is possible to make any light a strobe light through a proper driving circuit. Explained with Circuit Schematics.

Introduction

A light when made to blink or flash indeed looks pretty eye-catching and that’s the reason why they are used in number of places as a warning device or for decorations. However a strobe light in particular may also be considered a flashing light yet is uniquely different from ordinary light flashers. Unlike them in a strobe light the ON/OFF pattern is so optimized that it produces sharp dazzling pulsed flashes of light. There’s no doubt why they are mostly used in conjunction with fast music to enhance a party mood. Nowadays green lasers are being popularly used as a strobing device in party halls and gatherings and have become hot favorite among the new generation. Whether it’s LEDs, lasers or an ordinary filament bulb, all can be made to flash or rather strobe using an electronic circuit capable of producing the required pulsed switching in the connected lighting element. Here we will see how we can make any light a strobe light using a simple electronic circuit.

The following section will acquaint you with the circuit details. Let’s go through it.

Pulsating any Light to Produce Strobing Effect

Through one of my previous articles we came across a nice little circuit able to produce interesting strobe effects over a few of the connected LEDs. But this circuit is only suitable for driving low power LEDs and thus cannot be applied to illuminate big areas and premises. The proposed circuit allows you to drive not only LEDs but also powerful lighting agents like incandescent bulbs, lasers, CFLs etc.

The first diagram shows the most basic form of a multivibrator circuit using transistors as the main active components. The connected LEDs can be made to strobe by suitably adjusting the two potentiometers VR1 and VR2.

The above circuit forms the base for all the following circuits through some suitable modifications and additions.

For example if you want to illuminate and pulsate a small torch bulb using it, you would just need to do the simple modifications as shown in the second diagram. Here by adding a PNP power transistor and triggering it through the collector of T2, a torch bulb is easily made to strobe. Off course, optimum effect is achieved only through proper adjustment of the two Pots.

As already discussed already in the previous section, green laser pointers are pretty popular nowadays; the diagram illustrated shows a simple method of converting the above circuit into a pulsating green laser pointer strobe light. Here, T3 and T4 form a typical current controlled transistor configuration – a must when vulnerable lasers are involved. The selection of R6 can be critical and will decide the current limiting threshold for a safe operating of the laser. A wrong calculation may instantly roast your costly laser bulb. The following formula may be used for calculating R6:

U = 0.6/Ilaser,

Where U = Operating voltage of the laser and the circuit.

I (laser) = Maximum safe operating current of the laser device.

The next diagram shows how an AC mains lamp may be used as a strobing light source using the above circuit. Here a triac forms the main switching component receiving the required gate pulses from T2’s collector.

Thus we see that through the above circuit designs it becomes very easy to make any light a strobe light simply by doing the relevant modifications.

Parts List

R1, R4, R5 = 680 Ohms,
R2, R3 = 10K
VR1, VR2 = 100K pot
T1, T2 = BC547,
T3, T4 = BC557
C1, C2 = 10uF/25V
Triac = BT136
LEDs = as per choice

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