Conex Club Magazine - no.11 - 2003

Conex Club Magazine - no. 11 - 2003 - Development module AT89C2051

Reading time: 3 minute

The main topics presented

1. Development board - uC PIC

The K8048 kit is a multifunctional programmer made by Velleman, offered disassembled, for the PIC Flash family of microcontrollers from Microchip.

These can be (re) programmed very often, making the software upgrade easy. Different types of PIC uCs can be programmed (from 8-pin to 28-pin) and several LEDs and push-buttons make it easy to test uC programmed directly into the socket (s) of the K8048 programmer.

Other types of PIC microcontrollers (over 28 pins) can be programmed via the connector CPSI available to the module.

The PICPROG2 program is used as software, and the MPLAB source code compilation program, which can also be downloaded from the Microchip website -

2. AVR (I) microcontrollers - Description and use

Starting with this issue, Conex Club magazine makes a detailed presentation of the AVR series microcontrollers produced by the American company ATMEL, including both the hardware architecture, the set of instructions and programming specifications, as well as examples of simple applications, in order for the magazine's readers to understand how these components work.

Why AVR microcontrollers? Hardware and software facilities, low price, assemblers and compilers for making programs in free versions and available on the Internet, and last but not least the possibility of writing microcontrollers in a simple way, practically available to anyone.

In issue 3/2003 of The magazine presented the scheme of a programmer for the AVR series, which uses as a software element the program "Pony Prog", also available in free versions.

The AVR series has an architecture RISC (Reduced Instructions Set Computer), being dedicated to programming with the help of high level languages ​​(Basic, C / C ++, etc.), through dedicated compilers.

However, the programming in assembly language allows a strict control of the hardware resources and a better compaction of the elaborated programs, having as immediate effect the decrease of the necessary program memory.

Although a RISC structure has a smaller instruction set than the existing one in the case of a CISC (Complex Instructions Set Computer) structure, the AVR series has an extended instruction set, their number being at least 89.

The AVR family contains 6 basic constructive types, presented in table 1 (from the article).

3. AT89C2051 development module

The reader familiar with microcontrollers might ask the following question: why is a programmer presented for the "old" AT89C2051, when the latest generation microcontrollers can be programmed much easier, by connecting directly to the parallel port of a computer or, at most, by using a bus buffer?

The answer is simple: the very low price and the presence of flash memory, which allows 1000 write / read cycles, are advantages that make 2051 a circuit still quite used.

4. PWM Generator

The article is a presentation of the author's contribution to an online contest organized by Texas Instruments.

The assembly can be used to generate a signal with constant frequency, but with variable signal-pause ratio (variable period) - PWM signal. This signal has an average amplitude proportional to the duration of the duty cycle.

So, it can be said that this assembly is a digital-to-analog converter. The variable ratio between signal and pause is 1: 100, with a resolution of 1%. The frequency is quite stable and depends on the accuracy of the crystal in the oscillator.

Clock frequency - CLK is not critical. A clock frequency of 2.5MHz. After going through two counters, the clock frequency is divided by 100, and the PWM output signal will have a frequency of 25kHz.

This frequency is above the audio range and is suitable for DC motor control applications. The desired signal-to-pause ratio can be set with two digital BCD switches. The number that is set with these digital switches represents the signal duration ("1" logic). Basically, if you want to get a signal with 36% "1" logic and 64% "0" logic you have to set the switches to position 36.

The switches must be of type BCD. It is important not to make mistakes and to use appropriate 16-position switches.

5. Capacitometer

A tool that can measure capacities is always useful and welcome in the "laboratory" of every amateur electronician.

The device presented is relatively simple to make, uses components that are easy to purchase, and some of them are already available for amateurs.

This device can measure capacities from a few picarasites up to 200uF and is used together with an electronic multimeter provided with the 2000mV scale. The capacity value is measured in 6 ranges: 0-200pF, 0-2000pF, 0-20nF, 0-200nF, 0-2uF and 0-200uF.

The device is powered from a power source with a voltage of 5V, well stabilized and filtered. Figure 1 (from the article) shows the electrical diagram.

The basic principle of the capacitance consists in measuring the voltage with which a capacitor is charged, for a determined duration of time.

In order to ensure a good measurement accuracy, a generator piloted with a crystal with its own oscillation frequency of 4.43MHz.

6. Color TV sight generator

It presents a color wonder generator useful for electronics engineers working in TV service. The assembly offers several types of mirrors, color or A / D and is controlled by a PIC16F84 processor.


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