Schematic Reference

Saturday, October 25, 2014

Invisible Broken Wire Detector

Portable loads such as video cameras, halogen flood lights, electrical irons, hand drillers, grinders, and cutters are powered by connecting long 2- or 3-core cables to the mains plug. Due to prolonged usage, the power cord wires are subjected to mechanical strain and stress, which can lead to internal snapping of wires at any point. In such a case most people go for replacing the core/cable, as finding the exact location of a broken wire is difficult.

In 3-core cables, it appears almost impossible to detect a broken wire and the point of break without physically disturbing all the three wires that are concealed in a PVC jacket. The circuit presented here can easily and quickly detect a broken/faulty wire and its breakage point in 1-core, 2-core, and 3-core cables without physically disturbing wires. It is built using hex inverter CMOS CD4069.

Gates N3 and N4 are used as a pulse generator that oscillates at around 1000 Hz in audio range. The frequency is determined by timing components comprising resistors R3 and R4, and capacitor C1. Gates N1 and N2 are used to sense the presence of 230V AC field around the live wire and buffer weak AC voltage picked from the test probe. The voltage at output pin 10 of gate N2 can enable or inhibit the oscillator circuit.

When the test probe is away from any high-voltage AC field, output pin 10 of gate N2 remains low. As a result, diode D3 conducts and inhibits the oscillator circuit from oscillating. Simultaneously, the output of gate N3 at pin 6 goes ‘low’ to cut off transistor T1. As a result, LED1 goes off. When the test probe is moved closer to 230V AC, 50Hz mains live wire, during every positive half-cycle, output pin 10 of gate N2 goes high.

Thus during every positive half-cycle of the mains frequency, the oscillator circuit is allowed to oscillate at around 1 kHz, making red LED (LED1) to blink. (Due to the persistence of vision, the LED appears to be glowing continuously.) This type of blinking reduces consumption of the current from button cells used for power supply. A 3V DC supply is sufficient for powering the whole circuit.

Circuit diagram:

Invisible Broken Wire Detector Circuit Diagram

AG13 or LR44 type button cells, which are also used inside laser pointers or in LED-based continuity testers, can be used for the circuit. The circuit consumes 3 mA during the sensing of AC mains voltage. For audio-visual indication, one may use a small buzzer (usually built inside quartz alarm time pieces) in parallel with one small (3mm) LCD in place of LED1 and resistor R5. In such a case, the current consumption of the circuit will be around 7 mA.

Alternatively, one may use two 1.5V R6- or AA-type batteries. Using this gadget, one can also quickly detect fused small filament bulbs in serial loops powered by 230V AC mains.
The whole circuit can be accommodated in a small PVC pipe and used as a handy broken-wire detector. Before detecting broken faulty wires, take out any connected load and find out the faulty wire first by continuity method using any multimeter or continuity tester.

Then connect 230V AC mains live wire at one end of the faulty wire, leaving the other end free. Connect neutral terminal of the mains AC to the remaining wires at one end. However, if any of the remaining wires is also found to be faulty, then both ends of these wires are connected to neutral. For single-wire testing, connecting neutral only to the live wire at one end is sufficient to detect the breakage point.

In this circuit, a 5cm (2-inch) long, thick, single-strand wire is used as the test probe. To detect the breakage point, turn on switch S1 and slowly move the test probe closer to the faulty wire, beginning with the input point of the live wire and proceeding towards its other end. LED1 starts glowing during the presence of AC voltage in faulty wire. When the breakage point is reached, LED1 immediately extinguishes due to the non-availability of mains AC voltage.

The point where LED1 is turned off is the exact broken-wire point. While testing a broken 3-core rounded cable wire, bend the probe’s edge in the form of ‘J’ to increase its sensitivity and move the bent edge of the test probe closer over the cable. During testing avoid any strong electric field close to the circuit to avoid false detection.

Author: K. Udhaya Kumaran

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Transformer Less Power Supply Circuit Diagram

This clever design uses 4 diodes in a bridge to produce a fixed voltage power supply capable of supplying 35mA. All diodes (every type of diode) are zener diodes. They all break down at a particular voltage. The fact is, a power diode breaks down at 100v or 400v and its zener characteristic is not useful. But if we put 2 zener diodes in a bridge with two ordinary power diodes, the bridge will break-down at the voltage of the zener. This is what we have done. If we use 18v zeners, the output will be 17v4.

When the incoming voltage is positive at the top, the left zener provides 18v limit (and the left power-diode produces a drop of 0.6v). This allows the right zener to pass current just like a normal diode but the voltage available to it is just 18v. The output of the right zener is 17v4. The same with the other half-cycle. The current is limited by the value of the X2 capacitor and this is 7mA for each 100n when in full-wave (as per thiscircuit). We have 10 x 100n = 1u capacitance. Theoretically the circuit will supply 70mA but we found it will only deliver 35mA before the output drops. The capacitor should comply with X1 or X2 class. The 10R is a safety-fuse resistor.

Circuit diagram:

TransformerLess Power Supply Circuit Diagram

The problem with this power supply is the "live" nature of the negative rail. When the power supply is connected as shown, the negative rail is 0.7v above neutral. If the mains is reversed, the negative rail is 340v (peak) above neutral and this will kill you as the current will flow through the diode and be lethal. You need to touch the negative rail (or the positive rail) and any earthed device such as a toaster to get killed. The only solution is the project being powered must be totally enclosed in a box with no outputs.

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Thursday, October 23, 2014

Arduino Based Capacitive Touch Screen

Arduino based projects are quite complicated and is no cake walk for beginners in this field. Interfacing a tablet with the microcontroller is a daunting task. Let see how its done here.

The primary focus should be on using the appropriate drivers for the tablet. This makes it a USB host. As seen in the video, light can be a medium of communication between the tablet and the microcontroller. A photo diode or photoresistor is what is needed here and this should be pressed against the screen.

Building a touch sensing capability can help in providing communication between the microcontroller and the tablet. Capacitive touch screens function by sensing the capacitance changes on the screen. In this case, a large conductive brass plate is used to simulate touch. The surface area of the conductor used here to simulate the touch sould be large.

Testing can be done by touching the scrren with a wire and holding the other end. This may not work. This is made to work by sticking a piece of aluminum foil on to the screen and connecting the free end to the pin that is available on the arduino. The video shows the working of the capacitive touch screen. The setup is quite fragile and a little more circuitry could improve its reliability. Thus the capacitive touch screen is done.

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Panasonic Microwave Oven Inverter HV Power Supply

Nearly all Panasonic microwave ovens now use an Inverter, and are always labelled with “Inverter” on
the front.

The High Voltage Power Supply Unit (HV PSU)

The HV PSU measures 165mm x 105mm x 60mm and weighs 650g.

At left is the control daughter board. In front of that on the main board are the opto-isolators for the control and status signals brought out to the green connector. Back left is the rectified mains filter choke. The mains rectifier and switching transistors can just be seen on the heatsink behind the transformer. The mains filter capacitor is at right rear. The HV rectifiers and filters (doubler) are right front – white wires are the HV output from the transformer. The green wire is for grounding the HV +ve. The two lugs t right are for connecting HV -ve and heater to the magnetron. The winding thatcan be seen on the transformer is the primary and is made from 3mm finely stranded wire.

Here’s a view of the control end:

This is the high voltage end:

The circuit for the HV PSU is below

Notes about the circuit:
1. Apart from the block diagram, there is no information on the Inverter cont(o)rol circuit. The circuit itself is centred on one large, unmarked IC, so no help there.
2. The control and status signals seem to be a digital stream (2-3v suggestsa 5V data stream). They are opto-isolated because the majority of the circuit is at mains potential (**BEWARE**). The part that isn’t is at 4kV (*** REALLY BEWARE ***)
3. The mains input side is monitored for both current and (under) voltage. No indication of what the control circuit does with this information.
4. The mains filter capacitor (C702) is very small – only 4uF. In a “normal” switching supply, there is usually 220 or 470 uF in this position.
5. Q701 that does all the hard work is a very heavy duty IGBT – a GT60N90 - 900V @ 60 A. Q702 forms some sort of flywheel circuit. This circuit from a Toshiba IGBT application note looks similar:

6. The HV side has a full-wave doubler rectifier and is marked 4kV @ 300mA. Unlike the classic microwave oven transformers (where one side of the winding is grounded), this means that the secondary must be well insulated from ground on both sides. A simple reconfiguration of the rectifier (replace the caps with diodes) into a bridge circuit should yield 2kV @ 600mA (depending on the diode ratings)
7. The HV filter capacitors are only 8200 pF each, effectively giving 4100pF in the doubler. Considering that the inverter runs at about 30kHz, the reactance is equivalent to that of a 5uF capacitor at 50Hz.
8. The positive side of the HV is grounded, so it’s a –4kV supply. Don’t simply swap the ground from the positive to the negative to get a +4kV supply, as the core of the transformer is also connected to this ground trace and will suddenly rise to 4kV above ground with disastrous and potentially fatal results. Instead, reverse the polarity of the rectifier diodes to get +4kV.

Source : By David Smith VK3HZ (vk3hz (*at*) wia.org.au)

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Line Following Robot Sensor

This Line Following Robot sensor or surface scanner for robots is a very simple, stamp-sized, short range (5-10mm) Infrared proximity detector wired around a standard reflective opto-sensor CNY70(IC1). In some disciplines, a line following robot or an electronic toy vehicle go along a predrawn black line on a white surface. In such devices, a surface scanner, pointed at the surface is used to align the right track.

IC1 contains an infrared LED and a phototransistor. The LED emit invisible infrared light on the track and the phototransistor works as a receiver. Usually, black colored surface reflects less light than white surface and more current will flow through the phototransistor when it is above a white surface. When a reflection is detected (IR light falls on the phototransistor) a current flows through R2 to ground which generates a voltage drop at the base of T1 to make it conduct. As a result, transistor T2 start conducting and the visual indicator LED(D1) lights up. Capacitor C2 works as a mini buffer.

Line Follower Robot Scanner Schematic

After construction and installation, the scanner needs to be calibrated. Initially set P1 to its mechanical centre position and place the robot above the white portion of the track. Now slowly turn P1 to get a good response from D1. After this, fine tune P1 to reduce false detection caused by external light sources. Also ensure that the LED remains in off condition when the sensor module is on the blackarea. Repeat the process until the correct calibration is achieved.

The red color LED (D1) is only a visual indicator. You can add a suitable (5V) reed relay in parallel with D1-R4 wiring after suitable alterations to brake/stop/redirect the robot. Similarly, the High to low (H-L) transition at the collector of T2 can be used as a signal to control the logic blocks of the robot. Resistor R1 determines the operating current of the IRLED inside IC1. The sensing ability largely depends on the reflective properties of the markings on the track and the strength of the light output from IC1.

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Using LTC3601 3 3V DC Power Converter

This Dc power converter circuit is designed LTC3601 from Linear Technology and is capable to up to 1.5A output current at a 3.3V. The LTC3601 operating supply voltage range is from 4V to 15V making it suitable for a wide range of power supply applications. The operating frequency of the LTC3601 buck regulator is programmable from 800kHz to 4MHz with an external resistor enabling the use of small surface mount inductors.

The LTC3601 buck regulator can operate in two modes: Burst Mode operation and forced continuous mode to allow the user to optimize output voltage ripple, noise, and light load efficiency for a given application.

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Friday, October 17, 2014

Single IC Dual tones Siren Circuits Diagram

Double-tone Police sound Circuits Diagram

This circuit is intended for children fun, and can be installed on bicycles, battery powered cars and motorcycles, but also on models and various games and toys. With SW1 positioned as shown in the circuit diagram, the typical dual-tone sound of Police or Fire-brigade cars is generated, by the oscillation of IC1A and IC1B gates. With SW1 set to the other position, the old siren sound increasing in frequency and then slowly decreasing is reproduced, by pushing on P1 that starts oscillation in IC1C and IC1D.

The loudspeaker, driven by Q1, should be of reasonable dimensions and well encased, in order to obtain a more realistic and louder output. Tone and period of the sound oscillations can be varied by changing the values of C1, C2, C5, C6 and/or associated resistors. No power switch is required: leave SW1 in the low position (old-type siren) and the circuit consumption will be negligible.

Single -IC Dual-tones Siren Circuits Diagram

Parts:

R1,R3___470K   1/4W Resistors

R2______680K   1/4W Resistor

R4_______82K   1/4W Resistor

R5______330K   1/4W Resistor

R6_______10K   1/4W Resistor

R7_______33K   1/4W Resistor

R8________3M3  1/4W Resistor

C1,C5_____10µF  25V Electrolytic Capacitors

C2,C6_____10nF  63V Polyester Capacitors

C3_______100nF  63V Polyester Capacitor

C4_______100µF  25V Electrolytic Capacitor

D1-D3___1N4148  75V 150mA Diodes

IC1_____4093   Quad 2 input Schmitt NAND Gate IC

Q1______BC337   45V 800mA NPN Transistor

P1______SPST Pushbutton

SW1_____DPDT Switch

SPKR____8 Ohm Loudspeaker

B1______6V Battery (4 AA 1.5V Cells in series)

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