Conex Club Magazine - no.6 - 2005

Conex Club Magazine - no.6 - 2005 - uC PIC programming from series 12C / 12F

Reading time: 5 minute

The main topics presented

1. Elements of thermal management of electronic products

Configuring a suitable temperature profile for gluing surface mount components (SMD)

The technology of surface mounting (SMT) of passive and active electronic components was at the time of its introduction on the market and still represents a real revolution in the electronics industry, being considered a decisive factor in the direction of miniaturization of electronic products.

The main reason for the emergence of this technology was the desire of product manufacturers to streamline the area of ​​the printed circuit board and reduce the volume of electronic products.

As an example of reducing the size of the board, it can be said that for a single layer electronic module the use of SMDs leads to a double reduction of the PCB area.

If the components are arranged on both sides of the plate, the area can be reduced four times.

In addition to the small dimensions in the XOY plane, SMDs also have a significantly reduced height. The conclusion is that by using SMT components, by mounting them on both sides of the board and by increasing the "on-board" density, a reduction of up to 80% of the initial dimensions can be obtained, an absolutely remarkable result considering the requirements of electronics. current.

Under these conditions, mastering the aspects related to the thermal management of the gluing of surface-mounted components on the printed circuit board has become an essential factor in achieving the success of electronic products based on SMT technology.

Development of SMT electronic modules, in conditions of high reliability, involves the use of specific installations, devices and equipment, of high precision, able to ensure the assembly conditions of the components on the board, to achieve reliable soldering between components and board, to ensure soldering testing, detection and replacement of defective components and, finally, the verification and commissioning of the electronic module.

What is the purpose of the article?

This article aims to present some aspects related to the gluing of surface mounting components. Unlike hot air jet soldering, serial process of low productivity and high probability of generating imperfections and soldering defects, the use of a specialized oven with conveyor belt (figure 1 in the article) and multiple software configurable heating zones have major advantages from all points of view.

2. Generation of laboratory sinusoidal signals by direct digital synthesis - DDS. Circuit AD9851

Direct Digital Synthesis is the technique of obtaining sinusoidal signals whose frequency and amplitude can be precisely controlled, using a precise tactile source and a digital data processing system.

A simple command equation prescribes the frequency of the output signal. Once programmed, the quality of the generated signal depends only on the stability of the clock source (which influences the frequency of the generated sinusoidal signal) and its jitter (influences the stability of the amplitude of the generated sinusoidal signal).

The major advantages of DDS

  • setting the generated frequency with an accuracy of better than 1 Hz (typically 1uHz for a 48-bit frequency control word) and the signal phase with an accuracy of better than 1 degree (typically 0.22 degrees for a 14-bit phase control word );
  • very high speed of variation of the frequency or phase of the generated signal (typically 10 MHz for DDS serial control and 100MHz for parallel control);
  • elimination of manual operations for adjustment during commissioning and of the problems associated with the aging of the components present in the analog frequency synthesizers;
  • the exclusive digital control of the DDS chip allows the remote control, repetitive with the preset sampling rate, under the command of a microcontroller, process computer or PC;
  • if used as a quadrature synthesizer (with phase I sinusoidal signal output and anti-phase cosine sinusoidal) DDS allows precise control of I and Q outputs without requiring "pairing" of control parameters as in the case of IQ generation methods by pure software command implemented in a DSP (Digital Sample Processing) microcontroller.

3. uC PIC programming from series 12C / 12F - Tricks and practical tips

Development tools, tricks and practical tips regarding uC PIC programming from 12C and 12F series.

Programming or reprogramming (when physically possible) a 12C or 12F series PIC CPU is slightly different from the programming mode of a standard PIC CPU, such as 16F84, distinguished by several features.

Programming problems occur when using a serial programmer (JDM compatible). It should be emphasized that in the above mentioned CPU programming, with a development tool produced by Microchip, no such problems appear.

But what to do when we do not have professional programming tools and use the free versions offered on the Internet? The issues raised above will be answered in the article.

4. Digital tachometer

This device allows counting the number of revolutions per minute of a thermal engine of a car, truck, etc. for those vehicles that are not equipped with tachometers. It can be used on four-stroke or two-stroke engines.

Table 1 (from the article) presents the table that indicates the engine speed depending on the number of existing cylinders.

The electrical diagram is presented in figures 1 and 2 (from the article). The assembly is made of two separate boards: the board with the pulse counter (figure 1) and the one with displays (figure 2).

The counting is done in two separate cycles (controlled by the pulses from the engine ignition system): in the first cycle the pulses are counted, and in the second the counting result is displayed and the counter is reset, after which the cycle is resumed.

Speeds between 100 and 9.900t / min can be measured., and the displayed result will appear divided by 100. Only numbers indicating thousands of laps and hundreds of laps will be displayed. The displayed value must be correlated with the number of cylinders and the type of engine, according to the indications in table 1 (from the article).

The input is made at the IN terminals. The signal is collected from the electronic ignition block (if it exists), from the magnetic flywheel of the motor or, more precisely, from the circuit breaker (or from the transistor) that controls the ignition coils.

In modern vehicles there is an electronic assembly equipped with a power transistor that controls the ignition coils.

5. Electronic ringtone for LS1240A integrated circuit telephone

With the help of the specialized integrated circuit LS1240A (DIP-8 capsule), a telephone, electronic bell can be made, which connects directly to the telephone line. The installation does not affect the normal operation of the telephone device when a call is in progress.

The LS1240A integrated circuit is provided (internally) with a bridge rectifier for the alternating ring signal, with a block that allows the bell to operate only when a certain threshold of the ring signal is exceeded (which is at least 15V), with two tone generators and an output stage (amplifier) ​​for powering the buzzer.

6. ZCD - pulse generator synchronized with the voltage crossing of 220Vac / 50Hz through zero

For various applications, such as the control of modern power sources with thyristors or transistors, for example, the synchronization of the commands applied in grids (or bases) is done knowing the moment of zeroing of the supply voltage from the network. Schemes that satisfy this condition are called ZCD - Zero Crossing Detector.

Galvanic isolation at a ZCD circuit is an important aspect. In the diagram presented in the article, the isolation is performed with IC1. The mass of the network is separated from that of the pulse output. Synchronous, periodic pulses of 300us are obtained every 10ms, ie when the mains voltage passes through zero.


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