Conex Club Magazine - no.3 - 2004

Conex Club Magazine - no.3 - 2004 - Elements of analog electronics specific to the microcontroller

Reading time: 4 minute

The main topics presented

1. Powering audio amplifiers

Introduces himself design elements, examples and ways of sizing the elements of a power supply and two kits made by Conex Electronic.

One of the important elements in an audio system of any origin is the power supply.

The quality of the audio signal, the achievement of the maximum power delivered by the amplifier, the various protections are dependent on the power supply.

Most young electronicians, who are still discovering the secrets of electronics, are especially passionate about the audio field and do not know all the aspects of powering audio amplifiers, making mistakes, without knowing it, in practical use.

The answers to their various questions will be given throughout the article.

2. Frequency synthesizer with uC - VHF - Elements of design and practical realization (I)

In this first article on the topic of frequency synthesis, it is proposed the analysis of the physical phenomena that appear and the presentation of the design elements necessary for the practical realization of a frequency synthesizer.

In the following issues of the magazine, in consecutive articles, an example of the design, programming and practical realization of a frequency synthesizer in the VHF band will be presented.

In modern telecommunications equipment obtaining the working frequencies is done with the frequency synthesizer. This has become technically easy and efficient at the same time due to the development of specialized integrated circuit manufacturing technology, at an acceptable cost.

The frequency synthesizer-assisted equipment provides:

  • flexibility and ease of tuning on the frequencies used;
  • accuracy of the rated channel frequency;
  • stability of the nominal frequency, usually given by a precision quartz oscillator or a thermo-compensated quartz oscillator (TCXO);
  • the facility of automatic frequency processing in radiocommunication systems;
  • low power consumption;
  • small size and weight;
  • high reliability due to the low number of components.

This paper briefly explains the physical phenomena that occur and presents the main design elements necessary for the practical realization of a frequency synthesizer.

The frequency synthesizer is an automatic adjustment system, which permanently compares the frequency and phase of the signal entering the system with the frequency and phase of the signal leaving the system.

3. PIC microcontrollers - Presentation and programming (V)

Elements of analog electronics specific to the microcontroller

The analog part of the microcontroller is presented PIC16F628 </strong> Microcontroller. and an example: waveform generator. It would have been far too nice from the manufacturer, like PIC16F62x to have a 10-bit A / D converter, and this at the same price as the current one.

PIC16F676 </strong> Microcontroller. (approximately identical price) has this A / D converter, but it lacks (compared to PIC16F628) 4 pins, USART module, PWM module and 1kB of program memory.

In compensation, the manufacturer included in the microcontroller two common comparators and a voltage reference (obtained by dividing the supply voltage with a 4-bit multiplexer that controls a resistive network) to allow the authorized user to design his own analog interface. It's just a pale success and we'll see why later.

The two comparators in the PIC microcontroller are essentially two operational amplifiers (AO) with modest performance. With much smaller decal amplification in the open loop of an AO, higher offset voltage than a high-performance AO, and modest slew-rate, they usually require a positive reaction to speed up switching.

4. Probe for oscilloscope with 16 inputs

The presented assembly makes it possible to simultaneously display the logical states for maximum 16 entries, sufficient in the testing process of an integrated circuit of medium complexity.

The visualization is done on the screen of an oscilloscope respecting the configuration from the catalog of the CI pins (image drawn at the bottom of the electronic scheme).

The simplicity of the scheme as well as the suggestive way in which the display is made are reasons that urge the electronics engineer to make the device very useful in designing logic diagrams or checking the assembly of integrated circuits.

The entire architecture is designed around the circuit SN74150, an easy to use 16: 1 TTL multiplexer. The scanning of the 16 inputs is done at the frequency imposed by the oscillator made with three NAND gates and the RC group which has a high time constant necessary to clearly distinguish the position of the pins on the cathode ray tube.

5. Dual source with back-up battery and timer

The assembly shown is a dual voltage source, intended for access control applications, respectively for actuating and powering the electromagnetic locks (yalla).

Due to the back-up source function (via a battery) it is also recommended for use in alarm systems, emergency telephone calls, intercoms, etc.

The source has two voltage outputs, respectively 12Vdc / 300mA stabilized and adjustable (for powering the equipment - keyboard - access control, if necessary) and the other 12V, max. 3A unstabilized, for powering the electromagnetic yalla and, respectively, charging a back-up battery that has the capacity to 1.2Ah.

The yalla's power supply is monitored by a timer (made with LM555, in monostable configuration) with timing at start-up in the range 1… 20s, adjustable.

6. L296, L4960 and L4962 (I) - Switching sources

The L296, L4960 and L4962 integrated circuits are switching voltage stabilizers, produced by ST Microelectronics (SGS-Thomson).

They can deliver variable voltages between 5.1V and 40V at the output, at maximum currents of 4A (L296 and L296P), 2.5A (L4960) and 1.5A (L4962), respectively. They work in step-down configuration, the maximum input voltage being 50V.

7. AC power regulator - 2kW

The assembly presented, made in the form of a kit assembled by Conex Electronic, is a 2kW AC voltage regulator (VTA), recommended for supplying variable voltage to some resistive consumers (incandescent bulbs, radiators, etc.).

It is specified from the beginning that capacitive or inductive consumers, such as electric motors, cannot be supplied through this assembly.

8. Monitor for telephone line monitoring

There is an installation that allows permanent monitoring of the status of the fixed telephone line. Prevents "thefts" from the telephone line and informs about existing defects on it.

9. Quartz crystals (I)

There are two useful applications: interface for temperature measurement with a multimeter and a proximity switch with IR optocoupler.

Quartz resonators are widely used electronic components in electronic equipment in the field of communications, telemetry, measurements, data processing, industrial automation, etc.

They are part of oscillators and quartz filters, being used wherever it is necessary to obtain a high stability of the oscillation frequency, respectively in circuits such as time base to

Quartz crystal units they are based on their operation the inverse piezoelectric effect and are used due to the excellent combination between the piezoelectric properties and the mechanical, thermal and chemical properties of quartz.

Although they are passive components, quartz resonators are less well known even among electronics with above average theoretical and practical training.

They are less known in terms of their operation and how to use them in applications. Most of the time, quartz is used "by ear", or simply as simple resistors (although they are oscillating circuits that have many subtleties in operation!).


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