Schematic Reference

Detects clipping in preamp stages, mixers, amplifiers etc., Single LED display - 9V Battery supply unit

This circuit was intended to be used as a separate, portable unit, to signal by means of a LED when the output wave form of a particular audio stage is "clipping" i.e. is reaching the onset of its maximum permitted peak-to-peak voltage value before an overload is occurring. This will help the operator in preventing severe, audible distortion to be generated through the audio equipment chain. This unit is particularly useful in signaling overload of the input stages in mixers, PA or musical instruments amplification chains, but is also suited to power amplifiers. A careful setting of Trimmer R5 will allow triggering of the LED with a wide range of peak-to-peak input voltages, in order to suit different requirements. Unfortunately, an oscilloscope and a sine wave frequency generator are required to accurately setup this circuit. Obviously, the unit can be embedded into an existing mixer, preamp or power amplifier, and powered by the internal supply rails in the 9 - 30V range. The power supply can also be obtained from higher voltage rails provided suitable R/C cells are inserted. SW1 and B1 must obviously be omitted.

Parts:

R1_______________1M 1/4W Resistor (See Notes)
R2,R3,R8_______100K 1/4W Resistors
R4,R6___________10K 1/4W Resistors
R5_______________5K 1/2W Trimmer Cermet or Carbon
R7_______________2K2 1/4W Resistor
R9______________22K 1/4W Resistor
R10______________1K 1/4W Resistor (See Notes)
C1,C4__________220nF 63V Polyester Capacitors
C2_______________4p7 63V Ceramic Capacitor (See Notes)
C3_____________220µF 25V Electrolytic Capacitor
C5______________10µF 25V Electrolytic Capacitor (See Notes)
D1,D2________1N4148 75V 150mA Diodes
D3______________LED (Any dimension, shape and color)
Q1____________BC547 45V 100mA NPN Transistor
IC1___________TL062 Dual Low current BIFET Op-Amp (or TL072, TL082)
SW1____________SPST Toggle or Slide Switch (See Text)
B1_______________9V PP3 Battery (See Text)

Circuit operation:

The heart of the circuit is a window comparator formed by two op-amps packaged into IC1. This technique allows to detect precisely and symmetrically either the positive or negative peak value reached by the monitored signal. The op-amps outputs are mixed by D1 and D2, smoothed by C4, R7 and R8, and feed the LED driver Q1 with a positive pulse. C5 adds a small output delay in order to allow detection of very short peaks.

Notes:

• With the values shown, the circuit can be easily set up to detect sine wave clipping from less than 1V to 30V peak-to-peak (i.e. 15W into 8 Ohms). If you need to detect higher output peak-to-peak voltages, R1 value must be raised. On the contrary, if the circuit will be used to detect only very low peak-to-peak voltages, it is convenient to lower R1 value to, say, 220K omitting C2. In this way, the adjustment of R5 will be made easier.
• Using a TL062 chip at 9V supply, stand-by current drawing is about 1.5mA and less than 10mA when the LED illuminates. With TL072 or TL082 chips, current drawing is about 4.5mA and 13mA respectively.
• When using power supplies higher than 12V, the value of R10 must be raised accordingly.
• When using power supplies higher than 25V, the working voltage value of C5 must be raised to 35 or 50V.

Here is the circuit of a simple electric window charger. With a couple of minor circuit variations, it can be used as an electric fence charger too. A standard 12V, 7Ah sealed maintenance-free (SMF) UPS battery is required for powering the entire unit. Any component layout and mounting plan can be used. However, try to keep the output terminals of transformer X1 away from the circuit board. Timer NE555 (IC1) is wired as a free-running oscillator with narrow negative pulse at the output pin 3. The pulse frequency is determined by resistors R2 and R3, preset VR1 and capacitor C3. The amplitude of the output pulse can be varied to some extent by adjusting variable resistor VR1. You can vary the frequency from 100 Hz to 150 Hz. X1 is a small, iron-core, step-down transformer (230V AC primary to 12V, 1A secondary) that must be reverse connected, i.e., the secondary winding terminals of the transformer should be connected between the emitter and ground and the output taken across the primary winding.

Switch S1 is used for power ‘on’/‘off’ and LED1 works as a power-‘on’ indicator. LED2 is used to indicate the pulse activity. The output pulse from pin 3 of IC1 drives pnp transistor T1 into conduction for the duration of the time period. The collector of T1 is connected to the base of driver transistor T2 through resistor R5. When transistor T1 conducts, T2 also conducts. When T2 conducts, a high-current pulse flows through the secondary winding of transformer X1 to generate a very high-voltage pulse at the primary winding. This dangerously high voltage can be used to charge the window rails/fences. Ordinary silicon diode D1 (1N4001) protects T2 against high-voltage peaks generated by X1 inductance during the switching time. You can replace X1 with another transformer rating, and, if necessary, replace T2 with another higher-capacity transistor. The circuit can be used to charge a 1km fence with some minor modifications in the output section.

Caution:

• Take all the relevant electrical safety precautions when assembling, testing and using this high-voltage generator.

140mW into 32 Ohm loads, Ultra-low Distortion

Those wanting private listening to their music program should add this Headphone Amplifier to the Modular Preamplifier chain. The circuit was kept as simple as possible compatibly with a High Quality performance. This goal was achieved by using two NE5532 Op-Amps in a circuit where IC1B is the "master" amplifier wired in the common non-inverting configuration already used in the Control Center Line amplifier. IC1A is the "slave" amplifier and is configured as a unity-gain buffer: parallel amplifiers increase output current capability of the circuit. Two Headphone outputs are provided by J3 and J4. The ac gain of the amplifier was kept deliberately low because this module is intended to be connected after the Control Center module, which provides the gain sufficient to drive the power amplifier.

If you intend to use this Headphone Amplifier as a stand-alone device, a higher ac gain could be necessary in order to cope with a CD player or Tuner output. This is accomplished by lowering the value of R1 to 1K5. In this way an ac gain of 9 is obtained, more than sufficient for the purpose. Contrary to the two 15V positive and negative regulator ICs used in other modules of this preamp, two 9V devices were employed instead. This because the NE5532 automatically limits its output voltage into very low loads as 32 Ohm in such a way that the output amplitude of the amplified signal remains the same, either the circuit is powered at ±9V or ±15V. The choice of a ±9V supply allows less power dissipation and better performance of the amplifier close to the clipping point.

The input socket of this amplifier must be connected to the Main Out socket of the Control Center Module. As this output is usually reserved to drive the power amplifier, a second socket (J2) wired in parallel to J1 is provided for this purpose. As with the other modules of this series, each electronic board can be fitted into a standard enclosure: Hammond extruded aluminum cases are well suited to host the boards of this preamp. In particular, the cases sized 16 x 10.3 x 5.3 cm or 22 x 10.3 x 5.3 cm have a very good look when stacked. See below an example of the possible arrangement of the front and rear panels of this module.

Parts:

P1______________47K Log. Potentiometer (twin concentric-spindle dual gang for stereo)
R1_______________4K7 1/4W Resistor
R2______________12K 1/4W Resistor
R3,R4___________33R 1/4W Resistors
R5,R6____________4R7 1/4W Resistors
C1_______________1µF 63V Polyester Capacitor
C2,C5__________100nF 63V Polyester Capacitors
C3,C6___________22µF 25V Electrolytic Capacitors
C4,C7_________2200µF 25V Electrolytic Capacitors
IC1__________NE5532 Low noise Dual Op-amp
IC2___________78L09 9V 100mA Positive Regulator IC
IC3___________79L09 9V 100mA Negative Regulator IC
D1,D2________1N4002 200V 1A Diodes
J1,J2__________RCA audio input sockets
J3,J4__________6mm. or 3mm. Stereo Jack sockets
J5_____________Mini DC Power Socket

Notes:

• The circuit diagram shows the Left channel only and the power supply.
• Some parts are in common to both channels and must not be doubled. These parts are: P1 (if a twin concentric-spindle dual gang potentiometer is used), IC2, IC3, C2, C3, C4, C5, C6, C7, D1, D2, J3, J4 and J5.
• This module requires an external 15 - 18V ac (100mA minimum) Power Supply Adaptor.

Technical data:

Output power (1KHz sinewave):
32 Ohm: 140mW RMS
Sensitivity:
275mV input for 1V RMS output into 32 Ohm load (31mW)
584mV input for 2.12V RMS output into 32 Ohm load (140mW)
Frequency response @ 2V RMS:
Flat from 15Hz to 23KHz
Total harmonic distortion into 32 Ohm load @ 1KHz:
1V RMS and 2V RMS 0.0012%
Total harmonic distortion into 32 Ohm load @ 10KHz:
1V RMS and 2V RMS 0.0008%

Generates 4 short flashes, followed by a steady on light
Can drive LED Arrays at currents up to 1 Amp

Circuits of this kind are intended to drive LED Arrays in order to create more visibility and conspicuity when a vehicle is stopped or stopping. This circuit, in particular, will emit a visual alerting signal of 4 short flashes, followed by a steady on light that remains steady on as long as the brakes are applied.

Circuit operation:

IC1 internal oscillator generates a square wave whose frequency is divided 64 times by the flip-flops contained in the chip in order to obtain about 1 to 4Hz at pin #4: this is the LED Array flashing frequency and can be set to the desired value by means of R3. A positive signal at D1 Cathode stops the oscillator after 5 pulses are counted. C2 and R1 automatically reset the IC whenever the brakes are applied. Q1 is the LED Array driver: LEDs will be on when pin #4 of IC1 goes low.

Parts:

R1_____________10K 1/4W Resistor
R2____________220K 1/4W Resistor
R3____________500K 1/2W Trimmer, Cermet or Carbon
R4______________1K8 1/4W Resistor (See Note)
R5______________1K8 1/4W Resistor
C1_____________47µF 25V Electrolytic Capacitor
C2______________1µF 25V Electrolytic Capacitor
C3_____________10nF 63V Polyester Capacitor
D1___________1N4148 75V 150mA Diode
IC1____________4060 14 stage ripple counter and oscillator IC
Q1____________BC327 45V 800mA PNP Transistor (See Note)
SW1____________SPST Brake Switch
B1______________12V Vehicle Battery

Note:

• The transistor type suggested for Q1 will drive LED Arrays at currents up to 500mA. To drive Arrays requiring higher currents (up to 1A and even more) use a BD436 (32V 4A PNP Transistor) for Q1 and a 1K resistor for R4.

Here is a simple non-contact AC power monitor for home appliances and laboratory equipment that should remain continuously switched-on. A fuse failure or power breakdown in the equipment going unnoticed may cause irreparable loss. The monitor sounds an alarm on detecting power failure to the equipment. The circuit is built around CMOS IC CD4011 utilising only a few components. NAND gates N1 and N2 of the IC are wired as an oscillator that drives a piezobuzzer directly. Resistors R2 and R3 and capacitor C2 are the oscillator components. The amplifier comprising transistors T1 and T2 disables the oscillator when mains power is available. In the standby mode, the base of T1 picks up 50Hz mains hum during the positive half cycles of AC and T1 conducts.

This provides base current to T2 and it also conducts, pulling the collector to ground potential. As the collectors of T1 and T2 are connected to pin 2 of NAND gate N1 of the oscillator, the oscillator gets disabled when the transistors conduct. Capacitor C1 prevents rise of the collector voltage of T2 again during the negative half cycles. When the power fails, the electrical field around the equipment’s wiring ceases and T1 and T2 turn off. Capacitor C1 starts charging via R1 and preset VR and when it gets sufficiently charged, the oscillator is enabled and the piezobuzzer produces a shrill tone. Resistor R1 protects T2 from short circuit if VR is adjusted to zero resistance.

The circuit can be easily assembled on a perforated/breadboard. Use a small plastic case to enclose the circuit and a telescopic antenna as aerial. A 9V battery can be used to power the circuit. Since the circuit draws only a few microamperes current in the standby mode, the battery will last several months. After assembling the circuit, take the aerial near the mains cable and adjust VR until the alarm stops to indicate the standby mode. The circuit can be placed on the equipment to be monitored close to the mains cable.

Operating a stepper motor using a fixed (constant) voltage supply results in poor torque at high speeds. In fact, stepper motors tend to stall at fairly low speeds under such conditions. Several approaches can be used to overcome this problem, one of which is to use a constant current supply in place of the more conventional constant voltage supply. A disadvantage of many constant current supplies is that simple circuits are inefficient but that doesn't apply to switchmode supplies such as the circuit shown here.

Basically, this circuit is a conventional switchmode regulator adapted for constant current output and is specially designed for stepper motor drivers - although it could be used for other applications as well. The circuit works as follows: IC1 (LM2575T) and its associated components (D1, L1, C1, etc) operate as a switchmode power supply. Normally, for constant voltage operation, the output is connected - either directly or via a resistive divider - back to the feedback input (pin 4) of IC1.


In this circuit, however, Q1 senses the current flowing through R1 and produces a corresponding voltage across R3. This voltage is then fed to pin 4 of IC1. As a result, the the circuit regulates the current into a load rather than the voltage across the load. Only one adjustment is needed: you have to adjust VR1 for optimum stepper motor performance over the desired speed range. The simplest way to do this is to measure the motor current at its rated voltage at zero stepping speed and then adjust VR1 for this current. The prototype worked well with a stepper motor rated at 80O per winding and a 12V nominal input voltage. Some components might have to be modified for motors having different characteristics.

This circuit is designed to drive the 1W LEDs that are now commonly available. Their non-linear voltage to current relationship and variation in forward voltage with temperature necessitates the use of a 350mA, constant-current power source as provided by this supply. In many respects, the circuit operates like a conventional step-down (buck) switching regulator. Transistor Q1 is the switching element, while inductor L1, diode D1 and the 100mF capacitor at the output form the energy transfer and storage elements. The pass transistor (Q1) is switch-ed by Q2, which together with the components in its base circuit, forms a simple oscillator. A 1nF capacitor provides the positive feedback necessary for oscillation. The output current is sensed by transistor Q3 and the two paralleled resistors in its base-emitter circuit.


When the current reaches about 350mA, the voltage drop across the resistors exceeds the base-emitter forward voltage of transistor Q3 (about 0.6V), switching it on. Q3’s collector then pulls Q2’s base towards ground, switching it off, which in turn switches off the main pass transistor (Q1). The time constant of the 15kW resistor and 4.7nF capacitor connected to Q2’s base adds hysteresis to the loop, thus ensuring regulation of the set output current. The inductor was made from a small toroid salvaged from an old computer power supply and rewound with 75 turns of 0.25mm enamelled copper wire, giving an inductance of about 620mH. The output current level should be trimmed before connecting your 1W LED. To do this, wire a 10W 5W resistor across the output as a load and adjust the value of one or both of the resistors in the base-emitter circuit of Q3 to get 3.5V (maximum) across the load resistor.

A series diode is often used as a means of protecting equipment from accidental power supply reversal, particularly in battery-powered equipment. Due to forward voltage losses, this is sometimes impractical. One solution is to use an enhancement mode P-channel power Mosfet (Q1) in series with the positive supply rail. A device with low drain-source "on" resistance can be selected to minimize voltage losses, which in turn extends battery life and reduces heat dissipation.


Zener diode ZD1 must be included to protect against excessive gate-source voltage, while a 100kΩ resistor limits zener fault current. A second 100kΩ resistor across the output ensures that the gate doesn’t float when the input is disconnected. A series fuse and bidirectional transient voltage suppressor (TVS1) could be included to provide over-voltage protection, if desired. If common input & output grounds are unimportant, then a version of this circuit employing an N-channel power Mosfet in series with the negative (0V) rail could also be employed.

There will be instances where the currents from each supply will be unequal. Where this is the case, the resistor divider is not sufficient, and the +ve and -ve voltages will be unequal. By using a cheap opamp (such as a uA741), a DC imbalance between supplies of up to about 15mA will not cause a problem. However, we can do better with a dual opamp (which will cost the same or less anyway), and increase the capability for up to about 30mA of difference between the two supplies.

This logic probe can be selected to operate on TTL or CMOS logic levels, depending on switch S1. A string of resistors associated with switch S1 sets the threshold levels for a window comparator comprising IC1a and IC1b. Depending on whether the level applied to the probe is high or low, the window comparator turns on LED1 (high) or LED2 (low). The 1.2M and 680k resistors set the probe signal to a midrange value when the probe is open-circuit, thereby preventing either LED from being lit.


If a pulse signal is present, the output of IC1a will toggle the clock input of flipflop IC2a. This drives LED3 which either lights for each pulse or continuously, depending on the setting of switch S2. Finally, the outputs of IC1a & IC1b are connected by diodes D5 & D6 to the base of transistor Q1 which is connected to the Reset input of flipflop IC2b. This has a piezo sounder (not buzzer) connected between its Q and Q-bar outputs so that it produces a sound which echoes the input pulse signal.

We’ve all had occasion to be annoyed at inconsiderate dog owners whose animals relieve themselves on the private property of others. This problem can hardly be solved in a lasting manner using verbal (or even physical) means, so recourse to an electronic remedy is better and friendlier. The starting point for this circuit is a ready-made passive infrared sensor (PIR), such as can be found in inexpensive movement detectors. The relay contact of the PIR energizes the power supply of the circuit shown here. The power supply generates a voltage of around 15 V after rectification by D1-D4 and filtering by R1/C3 and R2/C2. This voltage powers a square-wave oscillator comprising IC1a, R3/C1 and IC1b (acting as a buffer). The two unnecessary gates are simply connected in series with the buffer, so that they work with defined levels.

The R-C network is dimensioned such that frequency of oscillation is greater than 20 kHz. The amplitude can be set using P1. An IC power amplifier follows the oscillator to amplify this tone to a level that will be deafening for dogs (and other small creatures). We use the ST Microelectronics TDA2030 (http://us.st.com/stonline/books/pdf/docs/1458.pdf),
The peripheral circuitry corresponds to the specifications in the data sheet. With a supply voltage of 15 V, the TDA2030 can generate around 5W into a 4Ω speaker. According to the data sheet, the supply voltage of the TDA2030 can be increased to as much as 30 V, at which level it generates a hefty 16W into 4Ω (or 11W into 8Ω).

However, the 4093 still must be operated at 15V, which is the maximum allowable supply voltage for a CMOS IC. In principle, any inexpensive piezoelectric tweeter whose frequency response extends past 20kHz can be used for the speaker; it should have the highest possible sound pressure level (>100dB). A suitable type is listed on page 626 of the Conrad Electronics catalog. The impedance of such speakers rises to around 40 to 50 Ω at 20 kHz, so it is naturally not possible to obtain the power listed in the data sheet using this circuit. Nevertheless, it should be more than enough to scare off dog and master.