Sine Wave To TTL Converter

As the title implies, the present circuit is intended to convert sinusoidal input signals to TTL output signals. It can handle inputs of more than 100 mV and is suitable for use at frequencies up to about 80 MHz. Transistor T1, configured in a common-emitter circuit, is biased by voltage divider R3–R5 such that the potential across output resistor R1 is about half the supply voltage. When the circuit is driven by a signal whose amplitude is between 100 mV and TTL level (about 2 V r.m.s.), the circuit generates rectangular signals. The lowest frequencies that could be processed by the prototype were around 100 kHz at an input level of 100 mV, and about 10 kHz when the input signals were TTL level.

Resistor R6 holds the input resistance at about 50 Ω, which is the normal value in measurement techniques. It ensures that the effects of long coaxial cables on the signal are negligible. If the converter is used in a circuit with ample limits, R6 may be omitted, whereupon the input resistance rises to 300 Ω.

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NTSC PAL TV Signal Identifier

This circuit is able to identify PAL and NTSC video signals. Its output is high for an NTSC signal and low if the signal is PAL. This output signal can be used, for example, to automatically switch in a colour subcarrier converter or some other device while an NTSC signal is being received. One application is for the reception from satellites of free-to-air TV signals, which in Australia generally contain a mixture of 625-line PAL and 525-line NTSC programs. Operation of the circuit is as follows.

IC1 is an LM1881 video sync separator which takes the video input signal and generates vertical synchronisation pulses.
For an NTSC signal, these pulses are 16.66ms apart, corresponding to the 60Hz field rate, while for a PAL signal they are 20ms apart, corresponding to the 50Hz field rate. The vertical sync pulses are fed into IC2a, the first of two dual retriggerable monostable multivibrators in the 74HC123A. IC2a has a period of very close to 17.9ms, set by the 200kO resistor and 0.22µF capacitor at pins 14 & 15. Because the monostable is retriggerable, NTSC sync pulses arriving every 16.66ms will keep its Q output, at pin 13, high.

Circuit diagram:

NTSC-PAL TV Signal Identifier Circuit Diagram

However PAL sync pulses arriving every 20ms will allow the Q output to go low after 17.9ms, before being triggered high again 2.1ms later. Thus an NTSC signal will give a constant high output while a PAL signal will result in a train of pulses 2.1ms wide. The Q output from IC2a is fed to the inverting input of IC2b, the second monostable, which has a period of about 0.5s, as set by the 270kO resistor and 4.7µF tantalum capacitor at pins 6 & 7. With its input constantly high, resulting from an NTSC signal, IC2b is not triggered and its Q output remains low.
However, the pulse train from a PAL signal will constantly retrigger it, so its Q output will remain high. The period of IC2b also effectively makes it a low-pass filter which removes spurious switching due to any input glitches. The output signal is taken from the Q-bar (inverted) output, so that an NTSC signal gives a high output, while PAL gives low. For the particular application for which the circuit was developed, diode D1 and the resistor network shown drive the base of an NPN switching transistor and relay. A dual-colour 3-lead LED can also be fitted to indicate NTSC (red) or PAL (green). Note that with no video input, the output signal is high and will indicate NTSC.

Source : www.extremecircuits.net

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Video Amplifier Circuit Diagram

The video amplifier in the diagram is a well-known design. Simple, yet very useful, were it not for the ease with which the transistors can be damaged if the potentiometers (black level and signal amplitude) are in their extreme position. Fortunately, this can be obviated by the addition of two resistors. If in the diagram R3 and R4 were direct connections, as in the original design, and P1 were fully clockwise and P2 fully anticlockwise, such a large base current would flow through T1 that this transistor would give up the ghost.

Circuit diagram:

Video Amplifier Circuit Diagram

Moreover, with the wiper of P2 at earth level, the base current of T2 would be dangerously high. Resistors R3 and R4 are sufficient protection against such mishaps, since they limit the base currents to a level of not more than 5 mA. Shunt capacitor C4 prevents R4 having an adverse effect on the amplification.

Author: L.A.M. Prins - Copyright: Elektor Electronics

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White LED Lamp

Nowadays you can buy white LEDs, which emit quite a bit of light. They are so bright that you shouldn’t look directly at them. They are still expensive, but that is bound to change. You can make a very good solid-state pocket torch using a few of these white LEDs. The simplest approach is naturally to use a separate series resistor for each LED, which has an operating voltage of around 3.5 V at 20 mA. Depending on the value of the supply voltage, quite a bit of power will be lost in the resistors. The converter shown here generates a voltage that is high enough to allow ten LEDs to be connected in series. In addition, this converter supplies a constant current instead of a constant voltage.


A resistor in series with the LEDs produces a voltage drop that depends on the current through the LEDs. This voltage is compared inside the IC to a 1.25-V reference value, and the current is held constant at 18.4 mA (1.25 V ÷ 68 Ω). The IC used here is one of a series of National Semiconductor ‘simple switchers’. The value of the inductor is not critical; it can vary by plus or minus 50 percent. The black Newport coil, 220 µH at 3.5 A (1422435), is a good choice. Almost any type of Schottky diode can also be used, as long as it can handle at least 1A at 50V. The zener diodes are not actually necessary, but they are added to protect the IC. If the LED chain is opened during experiments, the voltage can rise to a value that the IC will not appreciate.

Resistors:
R1 = 1kΩ2
R2 = 68Ω
Capacitors:
C1 = 100µF 16V radial
C2 = 680nF
C3 = 100µF 63V radial
Inductors:
L1 = 200µH 1A
Semiconductors:
D1 = Schottky diode type PBYR745 or equivalent
D2-D5 = zener diode 10V, 0.4W
D6-D15 = white LED
IC1 = LM2585T-ADJ (National Semiconductor)

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Dual Input Combining Stereo Line Amplifier

This circuit takes two separate line-level stereo (L & R) signals and combines them into one stereo (L & R) output, thus avoiding the need to switch between two pairs of input signals. In the author’s application, it is used to feed the stereo audio from a TV receiver and a DVD player into an external amplifier. The need for the circuit arose because of a design peculiarity in the TV receiver. The TV has four A/V inputs and one A/V output. AV1-AV3 accept composite or S-video plus stereo audio inputs and these feed into the TV’s A/V output. AV4 accepts Component video (Y/Pb/Pr) plus stereo audio but unlike AV1-AV3, its audio (and video) signals are not fed to the TV A/V output. The Y/Pb/Pr input was chosen for use with the DVD player because of its superior video quality, while the audio was to be fed to an external amplifier for improved reproduction.

Circuit diagram:

Dual Input-Combining Stereo Line Amplifier Circuit Diagram

However, manual switching was inconvenient, hence the genesis of this design. In use, the DVD player audio is fed in parallel to TV AV4 and to one input pair of the combining amplifier, while the TV audio output feeds the other input pair. The amplifier output goes to the external audio amplifier. There is no conflict between the two audio inputs because when AV4 (DVD player) is selected, there is no TV audio output. In all other modes, the DVD player is off. As shown, the circuit has a voltage gain of 1.5 times (3.5dB) but this can be altered as required by changing the two 15kW resistors. Input impedance is 10kW and the outputs are isolated from cable and amplifier input capacitance with 47W series resistors. The circuit can be powered from a regulated 12V DC plugpack.

Author: Garth Jenkinson - Copyright: Silicon Chip Electronics

Source : www.extremecircuits.net

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HQ Notch Filter Without Close Tolerance Components

A notch for a narrow frequency band of a few per cent or even less normally requires close-tolerance components. At least, that’s what we thought until we came across a special opamp IC from Maxim. In filters with steep slopes, the component tolerances will interact in the complex frequency response. This effect rules out the use of standard tolerance components if any useful result is to be achieved. The circuit shown here relocates the issue of the value-sensitive resistors that determine the filter response from ‘visible’ resistors to ready available integrated circuits which also make the PCB layout for the filter much simpler. The operational amplifiers we’ve in mind contain laser-trimmed resistors that maintain their nominal value within 1‰ or less. For the same accuracy, the effort that goes into matching individual precision resistors would be far more costly and time consuming. The desired notch (rejection) frequency is easily calculated for both R-C sections shown in Figure 1.

Figure 1. Special opamps incorporating laser-trimmed resistors.

Dividing the workload:

The circuit separates the amplitude and frequency domains using two frequency-determining R-C networks and two level-determining feedback networks of summing amplifier IC2, which suppresses the frequency component to be eliminated from the input signal by simple phase shifting. IC1 contains two operational amplifiers complete with a feedback network. The MAX4075 is available in no fewer than 54 different gain specifications ranging from 0.25 V/V to 100 V/V, or +1.25 V/V to 101 V/V when non-inverting. The suffix AD indicates that we are employing the inverting version here (G = –1). These ICs operate as all-pass filters producing a phase shift of exactly 180 degrees at the roll-off frequency f0. The integrated amplifier resistors can be trusted to introduce a gain variation of less than 0.1 %.

They are responsible for the signal level (at the notch frequency) which is added to the input signal by IC2 by a summing operation. However, they do not affect the notch frequency proper — that is the domain of the two external R-C sections which, in turn, do not affect the degree of signal suppression. In general, SMDs (surface mount devices) have smaller production tolerance than their leaded counter-parts. Because the two ICs in this circuit are only available in an 8-pin SOIC enclosure anyway, it seems logical to employ SMDs in the rest of the circuit as well. Preset P1 allows the filter to be adjusted for maximum rejection of the unwanted frequency component.

Figure 2. This deep notch is within reach using just 5%-tolerance resistors and 20%-tolerance capacitors.

R-C notch filter:

Using standard-tolerance resistors for R1 and R2 (i.e., 1%, 0806 style) and 10%-tolerance capacitors for C1 and C2 (X7R ceramic) an amount of rejection better than that shown in Figure 2 may be achieved. The notch frequency proper may be defined more accurately by the use of selected R-C sections. Pin 3 of IC2 receives a signal that’s been 90-degrees phase shifted twice at the notch frequency, while pin 1 is fed with the input signal. These two signals are added by way of the two on-chip resistors. IC2 is a differential precision operational amplifier containing precision resistor networks trimmed to an error not exceeding ±0.2‰. Here, it is configured as a modified summing amplifier with its inverting input, pin 2, left open.

For frequencies considerably lower than the resonance frequency f0 = 1 / (2 π R C) the capacitors present a high impedance, preventing the inverting voltage followers from phase-shifting the signal. At higher frequencies than f0, each inverting voltage follower shifts its input signal by 180 degrees, producing a total shift of 360 degrees which (electrically) equals 0 degrees. The phases of each all-pass filter behave like a simple R-C pole, hence shift the signal at the resonance frequency by 90 degrees each. The three precision amplifier ICs can handle signals up to 100 kHz at remarkably low distortion. The supply voltage may be anything between 2.7 V and 5.5V. Current consumption will be of the order of 250µA.

Source : www.extremecircuits.net

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Discrete Robot

This simple robot, which responds to light and avoids obstacles, can be built without using a microcontroller, programmer or PC. The only ‘special’ component in the circuit is a window discriminator (a fancy version of a window comparator). Resistors R1 and R2 in combination with light-dependent resistors LDR1 and LDR2 form a voltage divider (with the current being limited by R1 and R2 for bright light). Window discriminator TCA965 compares the mid-point voltage with an upper threshold value (adjustable using P1) and a lower threshold value (adjustable using P2). Outputs AU, AI, AO, and AA go High if the voltage lies below, inside, above or outside this window, respectively; otherwise they remain Low.

Output AA switches transistor T1, which drives the right-hand motor. The light-dependent resistors can be attached on the left and right sides of the vehicle, or at the front and rear. This causes the robot to turn to the right, due to the motor on one side being stopped, until the desired lighting relationship is restored. The vehicle will then continue to travel in a straight line until the lighting relationship again changes, at which point it will again turn, and so on. You can experiment with various behaviour patterns by using the other outputs of the window discriminator. If a transistor is provided for each of the AU and AO outputs of the TCA965, the robot can be made to travel toward or away from a light source, depending on the connections.

Using the window discriminator, the robot will operate under the rules of a three-point controller (left, straight ahead, or right). If you fit the light-dependent resistors in a box under the vehicle together with a light source, you can try to have the robot follow a black line on a white background. A reflective IR sensor enables the robot to respond to obstacles. This not as simple as it might seem, since the Sharp IS471 operates the IR LED with pulsed light and uses sophisticated detection processing. When an obstacle is detected, the output (pin 2) goes Low and blocks transistor T2. This causes the motor to stop, and the vehicle will rotate about the stationary wheel until the obstacle is no longer in its path.

The sensitivity of the IS471 can be set using P3. As its range is only around 10–15 cm, the vehicle must not travel too quickly, since otherwise it will not be able to avoid obstacles in time. This part of the circuit is also open for experimentation. If a relatively large and fast robot requires an obstacle detector (or isn’t fitted with the IS471), an ultrasonic detector can also be used. Suitable complete construction kits are available from Conrad, for example. You can also fit a suitable mechanical push-button switch mounted on a flexible rod. The obstacle detector can also drive a warning buzzer or a lamp; the circuit leaves lots of room for your own ideas. The circuit works over a wide range of supply voltages from 4.5 to 16 V.

If larger motors are used, transistors with increased power-handling capacity and heavier batteries are necessary. The author connected two 4.8-V rechargeable batteries in series and used BC388 transistors as drivers for Lego micro-motors. You can build the robot entirely according to what you have in your parts box. The mechanical elements can also be freely selected, but they partially determine the behavior and operation of the robot. The author’s robot is made from a Lego chassis with a prototyping board holding the circuitry attached using elastic bands. The motors are fitted on the left-hand and right-hand sides. The third wheel at the front can turn freely.

One problem must be mentioned: if an obstacle is detected while an incorrect lighting relationship is present, the vehicle remains standing. In this case, a bit of logic could be added to cause both motors to rotate in reverse. However, that would require directional switches for the motors or motor driver ICs (L293D). The simple circuit would become more complicated and larger, and at some point you would end up using a microcontroller after all - but that’s just the point of the story.

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RESISTOR TO REDUCE L200 POWER DISSIPATION ELECTRONIC DIAGRAM

RESISTOR TO REDUCE L200 POWER DISSIPATION ELECTRONIC DIAGRAM

Instead of in series with the input, the resistor R can be connected between pins 1 and 2 of the IC if the load is constant. You can see this in the right figure. This will make some part of the load current flows through the resistor and the other part through the device.

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Speaker Headphone Switch For PCs

If you need to use a headset with your PC, then you will know how frustrating it is continuously swapping over speaker and microphone cables. This is even worse if the PC is parked in a dark corner and the hard-to-read writing on the sound card sockets is covered in dust. This simple switch box eliminates all these problems. It sits on top of the desk and connects to the PC with stereo one-to-one cables. On the rear of the box are sockets for the PC speaker and microphone connections and the existing speakers. On the front of the box are the sockets for the headset microphone and headphones, an input for an external microphone and two switches. One switch is used to direct the sound card output from the PC to either the existing speakers or the headphones.

Circuit diagram:

Speaker-Headphone Switch Circuit Diagram For Computers

The second switch connects either the headset microphone or the external microphone to the input socket of the PC sound card. The switches used were 3 position 4 pole rotary switches with the last pole unused and adjusted for 2-position operation. All sockets were stereo 3.5mm types. This multiple switching arrangement is very flexible and is especially handy if you want to use an external microphone while monitoring with headphones. The ground wire as well as the left and right wires are all switched to prevent noise that could otherwise be induced into the microphone input through joining separate earths. For the same reason, a plastic case is used so that the earths of the sockets are not shorted together as would happen with a metal case. You will require two additional short stereo extension cables to connect the box to the PC.

Author: Leon Williams - Copyright: Silicon Chip Electronics

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Up Down Fading LED Circuit

This circuit drives a motor clockwise / anticlockwise via a pot and reduces the speed to zero when the pot is in mid-position. The current is limited to 200mA and the voltage across the motor is less than 6v, but the circuit shows the principle of Pulse Width Modulation (providing powerful bursts of current to the motor to create a high or low RPM under load) and both forward/reverse RPM via the H-bridge arrangement.

Circuit diagram:

 Up/Down Fading LED Circuit diagram

 

Source : 50-555Circuits

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Alarm Clock With Day Selector

This  circuit disables an alarm clock on Saturdays and Sundays when people like to sleep in but enables normal operation on Mondays to Fridays so that people rise in time for work or school. The core of the circuit is a 4017 decade counter which acts as the day counter and it is used in conjunction with a desk clock which acts the alarm and a watch module with alarm function which provides one clock pulse very day to the 4017. In operation, the watch module feeds a day pulse via transistor Q3 to the clock input of IC1. This has seven outputs connected via day switches (S1-S7) and diodes D3-D9 to Q1 which disables the alarm signal to the speaker via transistor Q2. LEDs1-7 indicate the actual day (if you forget!).

Circuit diagram:

Alarm Clock With Day Selector Circuit Diagram

To set the system, set the desk clock for the correct time and for the desired alarm time (eg, 6’o’clock). The watch module is set to the correct time and its alarm set to midnight. The day counter, IC1, is set to the correct day, as indicated by the LEDs, by pushing switch S12 and closing switch S8 or S9. S8 is normally left open to conserve the battery by leaving the LEDs off. As shown on the circuit, switches S1-S7 are set to sound the alarm on Mondays to Fridays and disable it on Saturday and Sunday. However, you can change the days to suit your work habits.

Author: Rasim Kucalovic - Copyright: Silicon Chip Electronics

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1963 Dodge Dart Electrical Wiring Diagram

1963 Dodge Dart Electrical Wiring Diagram

The Part of 1963 Dodge Dart Electrical Wiring Diagram: direction signal switch connector, cigar lighter, ammeter, heater blower switch, the stop light and direction signal, tail light, beam selector switch, light switch, luggage compartment, circuit breaker, gas gauge, backup light, printed circuit connector, parking brake warning light and switch, etc. Features: lower-priced, shorter wheelbase, full-size Dodge.

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1999 Lincoln Continental Wiring Diagram

1999 Lincoln Continental Wiring Diagram

The Part of 1999 Lincoln Continental Wiring Diagram: fuse junction panel, autolamps, multifunction
switch, hazard, lighting crtl module, shift lock actuator, hazard flasher, switch input, stoplamp, passenger, delaved exit, turn left/right

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Lit Motors Unveils Self Balancing Electric Vehicle C 1

Introducing the C-1, the world’s first gyroscopically-stabilized “rolling smart phone”. This vehicle combines the efficiency and freedom of a motorcycle with the safety and convenience of a car. Offering the “alternative to alternatives” on an exciting and safe platform, the C-1 transforms your daily commute into something to look forward to. Influenced by Scandinavian design, the exterior of the C-1 is both approachable and simple, enveloping the human in subtle curves, softened volumes, and lots of glass.

The overall design foundation is based on its waist line, which wraps around the vehicle’s circumference, and is grounded by the swooping rocker panel, highlighting its unique gyroscopic components. Discs of light glow from the wheel hubs, illustrating the electric hub motors. With design key words: “subtle”, “simple”, and “human”, the C-1 is as happy to be seen as it is to be touched.

The C-1 was designed with you in mind. Lit Motors’ human-centered approach to design makes sure that the experience of sitting in such a unique transportation device is both comfortable and spacious. Through numerous mock-ups and user studies, we determined how much space people want and need. There is even enough room in this device for a friend to ride in the back for short city excursions.

Using electronically-controlled gyroscopes located under the floor – generating over 1,300 ft.-lb. of torque – the C-1 balances at a stop and stays upright, even in a collision. In-hub, direct-drive electric motors (20 kW) provide power and regeneration, while center-hub steering keeps you pointed in the right direction. With a top speed of 100+ MPH and battery packs providing up to 200 miles per charge, the C-1 is perfect for commuters and city dwellers alike. As we are hard at work developing this concept for production, please be patient for the future. Expect to see the C-1 in showrooms by the end of 2014.

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Sensitized Solar Cells Based on Zinc Compounds

Researchers at the University of Basel in Switzerland say they have developed a new approach to producing environmentally sustainable photovoltaic devices. The research team developed a new method for producing dye substances and attaching them to the surface of titanium dioxide nanoparticles. With this they demonstrated that simple dye compounds based on zinc, a readily available metal, can be used.

 

Dye-sensitized solar cells (DSCs) consist of titanium dioxide, a semiconductor material coated with a colored dye. The dye absorbs sunlight and injects electrons into the titanium dioxide, which ultimately results in a photovoltaic current. Conventional DSCs use ruthenium dyes, but ruthenium is very rare and expensive. The research team showed that dyes made with abundant and relatively inexpensive copper are effective in DSCs, and that low-cost zinc compounds can also be used. Although the new devices are not yet especially efficient, the finding opens the way to new generations of DSCs with previously ignored dye types.

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12V DC to 220V 100W Inverter Circuit Diagram

12V DC to 220V 100W Inverter Circuit Diagram

This is 100W inverter circuit. It uses 4047 IC and IRF540 Mosfet instead of 2N3055 transistor. Power output is 100W from 2-3A transformer.

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Build a Doorbell Circuit For Deaf People

This circuit provides a delayed visual indication when a door bell switch is pressed. In addition, a DPDT switch can be moved from within the house which will light a lamp in the door bell switch. The lamp can illuminate the words "Please Wait" for anyone with walking difficulties.

 Doorbell Circuit Diagram

Notes:

The circuit uses standard 2 wire doorbell cable or loudspeaker wire. In parallel with the doorbell switch, S1, is a 1N4001 diode and a 12 volt 60mA bulb.

The bulb is optional, it may be useful for anyone who is slow to answer the door, all you need to do is flick a switch inside the house, and the bulb will illuminate a label saying Please Wait inside the doorbell switch or close to it.

The double pole double throw switch sends the doorbell supply to the lamp, the 22 ohm resistor is there to reduce current flow, should the doorbell switch, S1 be pressed while the lamp is on.

The resistor needs to be rated 10 watts, the 0.5 Amp fuse protects against short circuits.

When S2 is in the up position (shown as brown contacts), this will illuminate the remote doorbell lamp. When down, (blue contacts) this is the normal position and will illuminate the lamp inside the house. Switch S1 will then charge the 47u capacitor and operate the transistor which lights the lamp.

As a door bell switch is only pressed momentarily, then the charge on the capacitor decays slowly, resulting in the lamp being left on for several seconds. If a longer period is needed then the capacitor may be increased in value.

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Single Transistor Relay Toggle

The circuit below requires a double pole, double throw relay in conjunction with a single transistor to allow toggling the relay with a momentary push button. One set of relay contacts is used to control the load, while the other is used to provide feedback to keep the relay activated or deactivated. Several push buttons can be wired in parallel to allow toggling the relay from different locations.

In the deactivated state, the relay contacts are arranged so the 1000 uF capacitor will charge to about 2.7 volts. When the switch is closed, the capacitor voltage is applied to the transistor base through a 560 resistor causing the transistor to turn on and activate the relay. In the activated state, the relay contacts are arranged so the 3.3K resistor and 560 ohm resistor provide a continous current to the transistor base maintaining the activated state. While in the activated state, the capacitor is allowed to discharge to zero through the 1K resistor. When the switch is again closed, the capacitor will cause the transistor base to move toward ground deactivating the relay.

Single Transistor Relay Toggle  Circuit Diagram

The circuit has three distinct advantages, it requires only a few parts, always comes up with the relay deactivated, and doesnt need any switch debouncing. However since the capacitor will begin charging as soon as the button is depressed, the button cannot remain depressed too long to avoid re-engaging the relay. This problem can be minimized with an additional resistor connected from the transistor base to ground so that the base voltage is close to 0.7 volts with the button depressed and the transistor is biased in the linear region. With the button held down, the relay coil voltage should be somewhere between the pull in and drop out voltages so that the relay will maintain the last toggled state.

This worked out to about 820 ohms for the circuit I built using a 12 volt, 120 ohm relay coil and 2N3053 transistor. Temperature changes will effect the situation but the operation is still greatly improved. I heated the transistor with a hair dryer and found that the relay will re-engage with the button held down for approximately 1 second, but this is not much of a problem under normal operation.

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Switching Power Supply Using the LMZ14202H

Using the LMZ14202H power switching controller, can be designed a very simple switching power supply circuit that can provide a fixed output voltage covering a wide range of voltages .

Switching Power Supply Circuit diagram

This power switching power supply electronic project will provide a fixed output voltage between 5 and 30 volt from an input voltage between 8 and 42 volt at a maximum output current of 2 ampere . This circuit project power supply require few external electronic parts and can be configured very easy . In the table bellow you can see components value that are required for different output voltage

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SW Receiver Using MK414

A Short Wave Receiver based on the MK484 (formerly ZN414) that includes the tropical bands and 49 metre bands.

SW Receiver Using MK414 Circuit Diagram

Notes:
The original data sheet for the MK414 states a maximum working frequency is around 4 MHz. SW transmissions are so powerful that this receiver will work well with signals up to about 6 or 7 MHz. The 10k resistor controls the operating voltage for the IC which is critical for good performance.

Coil Details:
The tuned circuit consists of a variable capacitor and fixed air spaced coil. For the coil, I wound between 10 and 20 turns of wire on an empty tube of around 1.5 inches diameter. The turns were spaced so that the overall length was around 3 inches. The variable capacitor tuned 0 - 300 pF but there is plenty of scope for experiment here. One final point, you will need an external antenna to receive broadcasts. I have an outside wire that is about 7 meters long and this was quite effective. The antenna can be connected at either end of the coil or via a series capacitor value between 10pF and 100pF.

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Economy Radar Detector Circuit

Circuit Diagram

Description

This circuit uses a 1458 dual op-amp to form a radar detector. C1 is the detector of the radar signal. The first op-amp forms a current-to-voltage converter and the second op-amp buffers the output to drive the piezo transducer. R5 sets the switching threshold of the second op-amp; normally it is adjusted so that the circuit barely triggers on background noise, then its backed off a bit. The response of the circuit may be tuned by adjusting the length of the leads on C1. For typical road-radar systems, the input capacitors leads should be about 0.5 to 0.6 inches long.

Author: "Radio-Electronics" Magazine, Jul,86 issue (C) Copyright Gernsback Publications, Inc., 1986
 Source http://www.electronics-lab.com/

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Voltage Rating Tester for Zener Diode

I have teamed up with Magazine Mikro Elektronica for this project. Please visit their site. I am very grateful to Aleksandar Dakic for the kind translation into Serbian and Romanian languages.

Voltage Rating Tester for Zener Diode Circuit Diagram

Notes:
Using a single 555 Timer IC and a small transformer to generate a high voltage, this circuit will test zener diodes of voltage ratings up to 50VDC. The 555 timer is used in the astable mode, the output at pin3 drives a small audio transformer such as the LT700. This has a primary impedance of 1K and a secondary impedance of 8 ohms. Used in reverse the unloaded ac voltage is around 120volts ac. This is rectified by the 1N4004 diode and smoothed by the 2.2u capacitor which MUST be rated at 150 VDC. The zener under test is measured with a multimeter set to DC volts as shown. The load current switch enables the zener to be tested at 1 or 2mA DC. The rectified DC load, but a good zener should maintain the reading on the volt meter.

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