Conex Club Magazine - no.7-8 - 2005

Conex Club Magazine - no.7-8 - 2005 - 100W amplifier - mono and stereo

Reading time: 4 minute

The main topics presented

1. Laser telemetry

The measuring device consists of two distinct blocks:

  • the measurement module that contains the display (laser transmitter - ultrasonic receiver);
  • observer module (ultrasonic transmitter).

The measurement module emits a succession of laser pulses (light) at a frequency that the operator's eye can observe, in the form of a red dot (remains persistent on the retina).

This visible point is directed on the "observer" module at a certain distance "d". The observer in turn emits a train of ultrasonic pulses (ultrasonic frequency), and the measurement module counts the time required for these pulses to travel the distance "d".

The value is permanently displayed on a display, LCD for example and is expressed in centimeters.

2. Timed miniature fuses - FSK0_ Series

Timed fuses (miniature) are modern electronic components for protection in electronic circuits, easy to use and handle. The main advantage is the small size, they are specially designed for PCB mounting.

Compared to the classic timed fuses, in the glass capsule, the models from the FSK0_ series are smaller and does not require sockets for mounting (which in the classic version are voluminous).

The time response of the fuse is noticeable in the technical specifications: at a short or long duration overload current the response time differs - one hour at a current 50% higher than the nominal one, two minutes at a current twice higher than the nominal one or a few seconds (maximum 10) for a current almost three times higher. The fuse interrupts the circuit, practically almost instantaneously, at a current over ten times higher.

They ensure the protection of electronic circuits at high starting currents (transient starting mode) and nominal in permanent mode operation. As examples of use: switching voltage sources, circuits for starting electric motors, etc.

3. Universal electronic voltmeter with LCD display

The presented voltmeter offers LCD display, with indication on 3 1/2 digits. It is easy to calibrate (choosing the nominal value of 200mV or 2V scale head, is done by changing the value of only two resistors).

By adding relatively simple attachments, it can also be used as an ammeter. Similar measuring instruments are also commercially available, but this assembly made by you can be used for specific purposes and, especially, can be calibrated for high accuracy.

Figure 1 (from the article) shows the electrical diagram. The voltmeter uses the specialized integrated circuit for LCD display, respectively ICL7106. The analog signal to be measured is applied to the pins marked "IN HI" and "IN LO", respectively to pins 31 and 30 of the ICL71606.

4. 100W amplifier - mono and stereo

The power amplifier shown can be configured in mono (bridge) or stereo, providing a maximum power of 100W RMS, respectively 2 x 50W RMS. It is made with two integrated circuits, TDA1514A.

The TDA1514A integrated circuit, used for this amplifier, works in class AB. The internal electrical diagram, at the level of functional blocks is offered in figure 1 (from the article).

It is thus noted that each of the amplification stages corresponding to the output fumigates an RMS power of 48W, typically measured at the supply voltage. +/- 27.5V and 4 Ohm load (table 1 in the article);

The two operational amplifiers at the input have the reversing terminal connected externally to terminal 9, and the outputs together attack a second amplification stage. The output is characteristic of a counter-amplifier with transistors - class AB with bootstrap - with thermal protections and with power limitation (SOA - limitation to operation in the safe operation area of ​​the output characteristic).

The circuit also has MUTE and STAND-BY functions; maximum supply voltage +/- 30V, open loop gain of 30dB and input resistance of 20 kOhm.

5. 18 holiday schemes and applications

  • Vibration detector (shock);
  • Current and voltage source with L200;
  • Multimeter adapter for measuring RF inductors;
  • Precision signal generator with MAX038;
  • Video signal amplifier;
  • 30W / 60W audio amplifier with HEX-FET;
  • Constant current source for white LED lamp;
  • Electronic regulator relay;
  • Electromagnetic field detector;
  • Signaling device for attaching the seat belt in the car;
  • Twilight automaton for automobile;
  • Double voltage source +/- 5Vdc, maximum 1A, stabilized;
  • Double voltage source +/- 15Vdc and +/- 5Vdc, stabilized;
  • Signal detector or detector for crossing the voltage of the electrical network through zero (galvanically isolated);
  • Exponometer with LM3914 and bargraph with LEDs;
  • Electronic starter for fluorescent lamps;
  • Fixed source with LM317 for predetermined output voltage (or 78xx for non-standard voltage);
  • Speed ​​regulator at 220Vac.

6. Cable capacity meter

The proposed scheme is a capacitor that works with low frequency sinusoidal signals (400… 500Hz), for which the wavelength in the cable is of the order of hundreds of km.

The output of the device is linear and can be read on a scale of 2000mV of any voltmeter of direct current. Figure 2 (from the article) contains the electrical diagram of the capacitance meter, without the output voltmeter, which is shown symbolically.

The whole device is formed around an integrated circuit LM324, which contains 4 operational amplifiers with independent operation.

7. Adapter for measuring alternating voltages

Interface with precision rectifier for measuring alternating voltages and interfacing it with a microcontroller.

The measurement of alternating voltages with the help of an industrial microcontroller that has included an analog-to-digital converter (CAN) cannot be done directly, mainly for two reasons:

  • the CAN input accepts only positive voltages and in a well determined range of values ​​(usually OV… Vcc, where Vcc is the supply voltage to the controller);
  • in most cases, the galvanic isolation of the measuring part from the measured voltage is also required.

In addition, measuring a time-varying analog signal involves a large number of analog-to-digital conversions and laborious mathematical processing, so "a software complication" and an increase in response time.

Under these conditions it is obvious that the measurement must be performed by means of an adapter that meets the requirements of the measurement process. The diagram presented is based on integrated circuits LM741 and MC1458.

The offered solution has the following advantages:

  • uses a resistive divider (simple, cheap, self-compensated with temperature) as input element,
  • provides galvanic isolation through an optical element and allows the use as a measuring element of an industrial microcontroller without analog-to-digital converter, the information on the measured voltage value being in the form of a rectangular signal with a frequency proportional to this value.


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