Conex Club Magazine - no.12 - 2004

Conex Club Magazine - no.12 - 2004 - R232 interface - One wire

Reading time: 4 minute

The main topics presented

1. R232 interface - One wire

Mounting 100% compatible with the interface produced by Dallas-Maxim, DS9097U, allows you to read all iButton components using your PC.

Without going into details, regarding the operation of the components generically called iButton (of which the best known is the DS1820 temperature sensor), it must be specified that this standard was developed by Dallas (currently Maxim-Dallas Semiconductor) and tends to be imposed due to its flexibility.

O iButton component is characterized, in addition to the function performed (digital temperature sensor, humidity, switch, memory, etc.), by a unique UNIQUE identification number.

The data is transmitted serially, on a single wire (which can be fed remotely), on 9… 12 bits. This makes it possible to identify and read several sensors, with different functions, all connected (in parallel) on the same single-wire bus (two wires, with ground).

Significant savings are made on wiring, and Maxim-Dallas offers free software (a very important aspect, by the way) for various general applications.

Custom programs can be easily developed in various programming environments. IButton components can interface for reading, interpreting data and making command decisions, with general purpose microcontrollers or with the PC.

Going over this general introduction, absolutely necessary to become aware of a phenomenon, there will be an interface with the PC, the One-Wire bus.

2. Board for experiments with AT89C2051, AT90S1200, AT90S2313

A module was chosen for the presentation for the development of usual ATMEL uC experiments, respectively AT89C2051, AT90S1200 and AT902313 (20-pin uC).

The scheme is simple and does not require comments. For serial communication a MAX232. The editing is useful for those who are interested in watching the series on uC AVR programming.

3. AVR Microcontrollers (XIII) - Serial communication on the UART port of uC AT90S2313

This episode presents a concrete application, which uses the serial UART port of the AT90S2313 microcontroller, namely a dual module for transmitting / receiving commands, usable in automation systems.

Depending on the length of the transmission line, two hardware configurations are exposed: one intended for short distance communication (inter-application), up to 50 cm, in environments without electromagnetic noise and another in which communication can be done safely over distances of at least 10m.

Because two microcontrollers are used in the same scheme, the application belongs to the category of multiprocessor applications.

4. Thermal radiators - Physical sizing

It presents practical advice and the mathematical equipment necessary to choose the correct radiator for heat evacuation in electronic equipment.

The power generated by the electronic power components causes them to heat up. The heat produced can inadvertently raise the temperature of the monolithic structure, and heat evacuation is usually done with thermal radiators.

The heat dissipation capacity of the radiator depends on several factors: geometric dimensions, shape, metal, color, position of the cooling fins, forced cooling with fan.

All this will determine the main characteristic of the radiator: Radiator heat resistance - ambient, marked Rtra and expressed in [C / W].

How do we choose the thermal radiator?

The first step is the establishment of the maximum power dissipated by the component (diode, transistor, thyristor, triac, integrated circuit, etc.) in the scheme of use, denoted with Pdm [W].

The second step is the determination of the thermal resistance of the radiator - the environment, which must be (see magazine Conex Club no.3 / 1999).

5. Semi-duplex intercom system, on two wires

The intercommunication system presented is recommended for use in an apartment, making the acoustic connection between two rooms. Intercommunication can be between the living room and a study room, but very well the assembly can be used to supervise a child..

It is not without interest if the system is applied as an acoustic sensor, ie to highlight the noise produced by an intruder (security systems).

The entire intercom system between two points, with the main role of intercom, consists of two identical units that connect only by two wires, most certainly by a shielded cable.

6. Tester for UTP / STP cable and telephone

The application highlights the continuity of a cable for data transmission or its corresponding plug.

A tester for testing telephone or network cable routes - UTP is very useful in the installation and service activity in structured cabling.

Acquiring an industrial tester is an expensive activity, and making the one presented does not raise costs to more than 10 Euros. The components used are general purpose, discrete digital circuits. Microcontrollers are not used to generate signals for testing.

Respecting the imposed theme, the display is made on a bar graph with 10 LEDs. Of the ten LEDs on the bar graph, only eight are used to effectively display cable continuity (respectively short circuit, imperfect contact), the other two are used to signal the supply voltage and any screen on the network cable ( cable with screen, STP).

7. Controller for aquarium with uC PIC16F84

The application is intended to automate an aquarium. The advantage of using it is both relief of the aquarist of some tasks, as well as the precision with which it is replaced, as a result of the functions with which the assembly comes in addition.

The installation makes the electronically controlled (automated) aquarium a modern pool for fish, which successfully competes with the pools of companies specialized in the field, offered at prices inaccessible to some.

Application description

The basic elements of the application are a microcontroller PIC16F84 (4 MHz version) and a 2 x 20 character LCD display (based on the HD44780 controller).

The assembly fulfills the following functions:

  • electronic clock with display in hh: mm: ss (24 h) format;
  • programmable alarm (JP7);
  • aquarium thermometer (JP11);
  • room thermometer (JP12);
  • electronic control of a heater (simple, without thermostat) depending on the water temperature and the thermostating threshold (which is adjustable - JP5);
  • electronic control of the lighting installation by switching on at 09:00 and switching off at 23:00 (JP2);
  • electronic control of the cooling system (fans, for example) when the water temperature reaches the cooling threshold which is adjustable (JP4);
  • a digital output on which the microcontroller generates a "1" for 10us at 10:00 and another at 21:00, which can be used by a possible automatic feeding device (JP8).

8. Games of LED lights

Easy to build, with a cost of no more than 3 Euros for a single copy, the montages presented can delight your children and can be a well-deserved holiday gift.

These they can complete the ornament of the Christmas tree or they can "look" good at the window or the balcony of your apartment! The uses are multiple, and the construction is too simple not to be approached! There are practically two variants of LED light sets.


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