Liquid Crystal Display LCD Tester

Liquid-crystal displays come in all sorts and sizes, and this applies also to their pinouts. In fact, many of these displays cannot be used properly without the manufacturers’ documentation. But, of course, this can never be found when it is needed, and a small tester to unravel the terminals may, therefore, be found very handy. A liquid-crystal display consists of two thin sheets of glass, the facing surfaces of which have been given thin conducting tracks. When the glass is looked through at right or near-right angles, these tracks cannot be seen. At certain viewing angles, they become visible, however.

The space between the sheets of glass is filled with a liquid that, stimulated by an electric voltage, alters the polarization of the incident light. In this way, segments may appear light or dark and give rise to the display of lines or shapes. A segment may be tested by applying an alternating voltage of a few volts across it. Note that the application of a direct voltage will damage the display irreversibly: the resulting current will remove the tracks. The alternating voltage should contain not even a tiny direct voltage component. An alternating current also removes part of the tracks when the current flows in one direction, but restores it when the current flows in the opposite direction.

The tester described here consists of a square-wave generator that produces an absolutely symmetrical alternating voltage without any d.c. component. Most logic oscillators are incapable of producing a squarewave signal: they generate rectangular waveforms whose duty cycle hovers around the 50%. The 4047 used in the tester has a binary scaler at its output that guarantees symmetry. The oscillator frequency is about 1 kHz. It may be powered from a 3–9 V source. Normally, this will be a battery, but a variable power supply has advantages. It shows at which voltage the display works satisfactorily and also that there is a clear relationship between the level of the voltage and the angle at which the display is clearly legible.

The tester draws a current not exceeding 1 mA. The test voltage must at all times be connected between the common terminal, that is, the back plane, and one of the segments. If it is not known which of the terminals is the back plane, connect one probe of the tester to a segment and the other successively to all the other terminals until the segment becomes visible. Note, however, that there are LCDs with more than one back plane. Therefore, if a segment does not become visible, investigate whether the display has a second back plane terminal.

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Mains Slave Switcher II

As a guide, a one-inch reed switch with 40 turns reliably switched on with the current flowing through a 150-watt lamp (approx. 625 mA) but larger reeds may require more turns. If the master appliance draws less current (which is unlikely with power tools) more turns will be required. The reed switch is used to switch on transistor T1 which in turn switches the relay RE1 and powers the slave appliance. Since reed switches have a low mechanical inertia, they have little difficulty in following the fluctuations of the magnetic field due to the alternating current in the coil and this means that they will switch on and off at 100 Hz.

Circuit diagram:

Mains Slave Switcher II Circuit Diagram

C3 is therefore fitted to slow down the transistor response and keep the relay energised during the mains zero crossings when the current drawn by the appliance falls to zero and the reed switch opens. C1 drops the mains voltage to about 15 V (determined by zener diode D1) and this is rectified and smoothed by D2 and C2 to provide a d.c. supply for the circuit. The relay contacts should be rated to switch the intended appliance (vacuum cleaner) and the coil should have a minimum coil resistance of 400 R as the simple d.c. supply can only provide a limited current. C1 drops virtually the full mains voltage and should therefore be a n X2-class component with a voltage rating of at least 250V a.c.

Warning:

The circuit is by its nature connected directly to the mains supply. Great care should therefore be taken in its construction and the circuit should be enclosed in a plastic or earthed metal box with mains sockets fitted for the master and slave appliances.

Author: Elektor - Copyright: Elektor Electronics Magazine

Source : www.extremecircuits.net

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Build A Synchronous Clock

The quartz clocks which have dominated time-keeping for the past 20 years or so have one problem: their errors, although slight, are cumulative. After running for several months the errors can be significant. Sometimes you can correct these if you can slightly tweak the crystal frequency but otherwise you are forced to reset the clock at regular intervals. By contrast, mains-powered synchronous clocks are kept accurate by the 50Hz mains distribution system and they are very reliable, except of course, when a blackout occurs. This circuit converts a quartz clock to synchronous mains operation, so that you can have at least one clock in your home which shows the time. First, you need to obtain a quartz clock movement and disassemble it down to the PC board. For instructions on how to do this, see the article on a "Fast Clock For Railway Modellers" in the December 1996 issue of SILICON CHIP. Then isolate the two wires to the clock coil and solder two light duty insulated hookup wires to them (eg, two strands of rainbow cable). Drill a small hole in the clock case and pass the wires through them. Then reassemble the clock case.

Circuit diagram:

A Synchronous Clock Circuit Diagram

To test the movement, touch the wires to the terminals of an AA cell, then reverse the wires and touch the cell terminals again. The clock second hand should advance on each connection. The circuit is driven by a low voltage AC plug pack. Its AC output is fed to two bridge rectifiers: BR1 provides the DC supply while BR2 provides positive-going pulses at 100Hz to IC1a, a 4093 NAND Schmitt trigger. IC1a squares up the 100Hz pulses and feeds them to the clock input of the cascaded 4017 decade counters. The output at pin 12 of IC3 is 1Hz. This is fed to IC4, a 4013 D-type flipflop, which is connected so that its two outputs at pins 12 & 13 each go positive for one second at a time. As these pulses are too long to drive the clock movement directly, the outputs are each fed to 4093 NAND gates IC1b & IC1c where they are gated with the pin 3 signal to IC4. This results in short pulses from pins 3 & 10 of IC1 which drives the clock via limiting resistor R1. The value of R1 should be selected on test, allowing just enough current to reliably drive the clock movement.

Author: A. J. Lowe - Copyright: Silicon Chip

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Antenna Tuning Unit ATU For 27 MHz CB Radios

This antenna tuning unit (ATU) enables half-wavelength or longer wire antennas to be matched to the 50-? antenna input of 27-MHz Citizens’ Band (CB) rigs. The ATU is useful in those cases where a wire antenna is less obtrusive than a roof-mounted ‘vertical’ or ground-plane. It is also great for ‘improvised’ antennas used by active CB users on camping sites and the like because it allows a length of wire to be used as a fairly effective antenna hung between, say, a tree branch at one side and a tent post, at the other. Obviously, the wire ends then have to be isolated using, for example, short lengths of nylon wire. It is even possible to use the ATU to tune a length of barbed wire to 27 MHz. The coil in the circuit consists of 11 turns of silver-plated copper wire with a diameter of about 1 mm (SWG20).

The internal diameter of the coil is 15 mm, and it is stretched to a length of about 4 cm. The tap for the antenna cable to the CB radio is made at about 2 turns from the cold (ground) side. Two trimmer capacitors are available for tuning the ATU. The smaller one, C1, for fine tuning, and the larger one, C2, for coarse tuning. The trimmers are adjusted with the aid of an in-line SWR (standing-wave ratio) meter which most CB enthusiasts will have, or should be able to obtain on loan. Select channel 20 on the CB rig and set C1 and C3 to mid-travel. Press the PTT button and adjust C2 for the best (that is, lowest) SWR reading. Next, alternately adjust C3 and C2 until you get as close as possible to a 1:1 SWR reading.

C1 may then be tweaked for an even better value. No need to re-adjust the ATU until another antenna is used. In case the length of the wire antenna is exactly 5.5 metres, then C3 is set to maximum capacitance. Although the ATU is designed for half-wavelength or longer antennas, it may also be used for physically shorter antennas. For example, if antenna has a physical length of only 3 metres, then the remaining 2.5 metres has to be wound on a length of PVC tubing. This creates a so-called BLC (base-loaded coil) electrically shortened antenna. In practice, the added coil can be made somewhat shorter than the theoretical value, so the actual length is best determined by trial and error. Finally, the ATU has to be built in an all-metal case to prevent unwanted radiation. The trimmers are than accessed through small holes. The connection to the CB radio is best made using an SO239 (‘UHF’) or BNC style socket on the ATU box and a short 50-W coax cable with matching plugs.

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Speach Amplifier Circuit Diagram

This circuit is intended to be placed in the same box containing the loudspeaker, forming a compact microphone amplifier primarily intended for speech reinforcement. A device of this kind is particularly suited to teachers, lecturers, tourists guides, hostesses and anyone speaking in crowded, noisy environment.

The circuits heart is formed by the TDA7052 Audio power amplifier IC, delivering a maximum output of 1.2W @ 6V supply. An external microphone must be plugged into J1, its signal being amplified by Q1 and fed to IC1. R1 acts as a volume control and C3 tailors the upper audio frequency band, mainly to reduce the microphone possibility of picking-up the loudspeaker output, causing a very undesirable and loud "howl", i.e. the well known Larsen effect. Therefore, C3 value can be varied in the 4n7 - 22nF range to ensure the best compromise from speech tone quality and minimum Larsen effect occurrence. Dynamic or electrets microphone is warmly recommended. It has a useful feature that can be used to momentarily mute the microphone by connecting SW1 shown in diagram.

Circuit Diagram:

 Speach Amplifier Circuit Diagram

Parts	Description
R1	22K
R2	1M
R3	15K
R4	470R
R5	47K
R6	4.7K
C1	100nF-63V
C2	100nF-63V
C3	100nF-63V
C4	10nF-63V
C5	220uF-25V
C6	10uF-25V
Q1	BC547
IC1	TDA7052 B1
J1	Mono Jack Socket
B1	6V Battery
SW1	SPST Slider Switch
SW2	SPST Toggle Switch

Notes:

• Please note that hands-free, uni-directional headset or ear clip microphone types are very well suited for this device, as also are Clip-on Lavaliere or Lapel microphones.
• If a small electrets capsule is used for the microphone, R5, R6 and C6 must be added to the circuit to provide power supply.
• Choose a loudspeaker as large as possible, in order to increase circuit performance.
• You can use also two 4 Ohm loudspeakers wired in series or two 8 Ohm types wired in parallel in order to obtain better results.
• The box containing the amplifier and loudspeaker(s) can be fitted out with a belt and carried like a shoulder-bag or, if you build a smaller unit, it can be used as a Pick & Go Belt Clip Speaker.

Source : www.redcircuits.com

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Fuse Box BMW 318i 1995 Diagram

Fuse Box BMW 318i 1995 Diagram - Here are new post for Fuse Box BMW 318i 1995 Diagram.

Fuse Box BMW 318i 1995 Diagram

Fuse Panel Layout Diagram Parts: hazard flasher relay, low beam light relay, high beam light relay, blower relay, front fog light relay, horn relay.

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4 20mA Current Loop Tester

This design will interest technicians who work on pneumatically operated valves and other 4-20mA current loop controlled devices. Although 4-20mA signal injector/calibrators are available, this one is both cheap to build and easy to operate. When first powered up, the circuit sinks 4mA of current. If switch S1 is pressed, the current level slowly ramps up to 20mA, pauses and then ramps back to 4mA. This cycle will continue unless the switch is pressed again, whereby the output will lock to its current level. A further push of the switch resumes the prior cyclic operation. Output2 from the micro (IC1) is programmed to generate a pulse-width modulated (PWM) signal to drive the current sink transistor (Q1).


The digital PWM signal is converted to an analog voltage using a low-pass filter formed by the 1kω series resistor and a 4.7μF tantalum capacitor. By varying the PWM duty cycle and therefore the DC signal level out of the filter, the program can indirectly vary the current flow through the transistor. A 100 resistor in series with the emitter of Q1 converts the loop current to a small voltage, which is fed into the micro on input1. The program uses this feedback signal to zero in on the desired current level with the aid of the micros analog-to-digital converter. Details of this can be seen in the accompanying program listing.

If the PICAXE senses an open circuit, it shuts down the output and goes into an alarm state, to alert the operator and protect the circuit under test. The switch can be pressed to reset operations to the start once the open circuit has been rectified. The LED flashes a code for various milestones, as follows: one flash at 4m and one flash to confirm a switch press two flashes at 12m when ramping up (for the first 5 cycles); three flashes at 20m and continued fast flash sequence for open-circuit alarm. For portable use, the circuit can be powered from two 9V batteries, whereas for bench testing, a 12V DC plugpack will suffice.

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LED Volt Meter Circuit

Here is a Simple LED Volt meter to Monitor the charge level in Lead Acid Battery or Tubular battery. The terminal voltage of the battery is indicated through a four level LED indicators. The nominal terminal voltage of a Lead Acid battery is 13.8 volts and that of a Tubular battery is 14.8 volts when fully charged. The LED voltmeter uses four Zener diodes to light the LEDs at the precise breakdown voltage of the Zener diodes. Usually the Zener diode requires 1.6 volts in excess than its prescribed value to reach the breakdown threshold level. When the battery holds 13.6 volts or more, all the Zener breakdown and all LEDs light up. When the battery is discharged below 10.6 volts, all the LEDs remain dark. So depending on the terminal voltage of the battery, LEDs light up one by one or turns off.

Circuit diagram:

 LED Volt Meter Circuit Diagram

Author: D. Mohan Kumar Copyright: electroschematics.com

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Adjustable Zener Diode

A Zener diode is the simplest known type of voltage limiter (Figure 1) As soon as the voltage exceeds the rated voltage of the Zener diode, a current can flow through the diode to limit the voltage. This is exactly the right answer for many protection circuit applications. However, if it is necessary to limit a signal to a certain voltage in a control circuit, Zener diodes do not provide an adequate solution. They are only available with fixed values, which are also subject to a tolerance range. What we are looking for is thus an ‘adjustable’ Zener diode. Such a component would be useful in a heating controller with a preheat temperature limiting, for example, or in a battery charger to provide current limiting. The answer to our quest is shown in Figure 2. Assume for example that the output voltage must not exceed 6.5 V. The control voltage on the non-inverting input is thus set to 6.5 V.

Now assume that 4.2V is present at the input. The result is that the maximum positive voltage is present at the opamp output, but the diode prevents this from having any effect on the signal. However, if the voltage rises above 6.5V, the output of the opamp goes negative and pulls the voltage back down to 6.5 V. The current is limited by R3. Another example is a situation in which exactly the opposite is required. In this case, the voltage must not drop below a certain value. This can be easily achieved by reversing the polarity of the diode. Another option is a voltage that is only allowed to vary within a certain voltage window. It must not rise above a certain value, but it also must not drop below another specific value. In the circuit shown in Figure 3, the left-hand opamp provides the upper limit and the right-hand opamp provides the lower limit. Each opamp is wired as a voltage follower.

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Model Railway Short Circuit Beeper

Short circuits in the tracks, points or wiring are almost inevitable when building or operating a model railway. Although transformers for model systems must be protected against short circuits by built-in bimetallic switches, the response time of such switches is so long that is not possible to immediately localise a short that occurs while the trains are running, for example. Furthermore, bimetallic protection switches do not always work properly when the voltage applied to the track circuit is relatively low. The rapid-acting acoustic short-circuit detector described here eliminates these problems. However, it requires its own power source, which is implemented here in the form of a GoldCap storage capacitor with a capacity of 0.1 to 1 F. A commonly available reed switch (filled with an inert gas) is used for the current sensor, but in this case it is actuated by a solenoid instead of a permanent magnet.

An adequate coil is provided by several turns of 0.8–1 mm enamelled copper wire wound around a drill bit or yarn spool and then slipped over the glass tube of the reed switch. This technique generates only a negligible voltage drop. The actuation sensitivity of the switch (expressed in ampère-turns or A-t)) determines the number of turns required for the coil. For instance, if you select a type rated at 20–40 A-t and assume a maximum allowable operating current of 6 A, seven turns (40 ÷ 6 = 6.67) will be sufficient. As a rule, the optimum number of windings must be determined empirically, due to a lack of specification data. As you can see from the circuit diagram, the short-circuit detector is equally suitable for AC and DC railways. With Märklin transformers (HO and I), the track and lighting circuits can be sensed together, since both circuits are powered from a single secondary winding.

Coil L1 is located in the common ground lead (‘O’ terminal), so the piezoelectric buzzer will sound if a short circuit is present in either of the two circuits. The (positive) trigger voltage is taken from the lighting circuit (L) via D1 and series resistor R1. Even though the current flowing through winding L1 is an AC or pulsating DC current, which causes the contact reeds to vibrate in synchronisation with the mains frequency, the buzzer will be activated because a brief positive pulse is all that is required to trigger thyristor Th1. The thyristor takes its anode voltage from the GoldCap storage capacitor (C2), which is charged via C2 and R2.

The alarm can be manually switched off using switch S1, since although the thyristor will return to the blocking state after C2 has been discharged if a short circuit is present the lighting circuit, this will not happen if there is a short circuit in the track circuit. C1 eliminates any noise pulses that may be generated. As a continuous tone does not attract as much attention as an intermittent beep, an intermittent piezoelectric generator is preferable. As almost no current flows during the intervals between beeps and the hold current through the thyristor must be kept above 3 mA, a resistor with a value of 1.5–1.8 kΩ is connected in parallel with the buzzer. This may also be necessary with certain types of continuous-tone buzzers if the operating current is less than 3 mA. The Zener diode must limit the operating voltage to 5.1 V, since the rated voltage of the GoldCap capacitor is 5.5V.

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