Conex Club Magazine - no.10 - 2004

Conex Club Magazine - no. 10 - 2004 - Electrical route detector for 220Vac

Reading time: 4 minute

The main topics presented

1. Portable GPS with LCD display

GPS applications are innumerable and have implications in extremely diverse fields, from telecommunications and IT, to agriculture or tourism.

It will be described a simple application made with the GPS module TRIMBLE Lassen SQ, probably small in size but also more affordable in price.

The assembly described (figure 1 in the article) consists of a GPS receiver TRIMBLE Lassen SQ, a microcontroller PIC16F628 </strong> Microcontroller. and an LCD display with 2 × 16 alphanumeric characters.

The information provided by GPS are, among others: time and date - synchronized UTC, latitude, longitude, speed, altitude, direction of travel.

This data is retrieved by the CPU, processed and then displayed on the LCD display in several pages selectable using the SW1 switch.

2. Elements of thermal management of electronic products (II)

The development of a temperature monitoring equipment in the technological processes with uC is presented PIC16F877 </strong> Microcontroller..

Because the monitoring equipment uses multi-point measurement based on thermocouples, In this article we will make a brief treatment of the principle of operation of thermocouples.

Thus, the operation of these transducers is based on the thermal gradient theory.

As shown schematically in figure 4 (from the article), when one of the ends of a conductor is heated, an electrical voltage is generated, depending on the thermal gradient and the metal from which the respective conductor is made.

Thermocouples are made of two conductors made of different metals / alloys which are welded at one end (figure 5 of the article).

The voltage that appears at the other end of the thermocouple depends on the temperature of the junction (welding) and the type of metals / alloys from which the conductors are made.

All pairs of dissimilar metals have this property, called "Seebeck" voltage, after the name of the person who discovered the phenomenon, Thomas Seebeck.

3. Temperature transducers (III) - Semiconductor transducers

Presentation of digital semiconductor temperature transducers, DS56 and LM75 and practical applications with them.

The idea of ​​having circuits for measuring temperature and processing the signal on the same "chip" is older.

Previous implementations were limited to pn junction type sensors and analog processing circuits that delivered either a temperature-dependent current or a voltage. The current trend is to have numerically available information at the output.

DS56 - Dual Temperature Comparator

DS56, named by the manufacturer double temperature comparator it includes a temperature sensor, a voltage reference and two comparators.

This circuit can be used both for temperature measurement and as a thermostat or temperature indicator at two points.

The circuit has an output where the voltage signal is dependent on the temperature of the capsule, an output that can be used independently of the temperature comparators.

It is thus possible to measure the temperature with an external circuit and have, for example, two thresholds: one to warn of exceeding a temperature and to start a cooling fan and another threshold, to stop, if the temperature rises above that of -the second limit.

Circuit accuracy is acceptable: +/- 2C for temperatures between 0… + 85C and at most +/- 3C for temperatures between -40… 0C and + 85… + 125C.

Another integrated circuit is LM75 (or DS75 from Dallas). If the DS56 is closer to the concept of analog temperature-dependent signal processing, the DS75 is truly a digital temperature transducer.

LM75 - 2-Wire Serial Temperature eSensor and Monitor

The block diagram (figure 5 in the article) confirms what has been said. The LM75 has a serial interface (data and clock) compatible with I2C and is addressable (it has three terminals from which the addresses can be configured) allowing the connection on a common bus of at most eight circuits.

The circuit comprises a converter 9-bit A / D (LM75) or 12-bit (DS75) and a comparator to which the actuation threshold and hysteresis can be programmed (on the serial line).

The output, also open-drain, is configurable (active down or active up). leaching can absorb a typical current of 2… 3mA, but it is recommended to use a lower current so as not to affect the accuracy.

4. Thermometer and precision thermostat with LM135

By the special precision of the temperature reading (0.1C) and of the thermostat with adjustable hysteresis, starting from 0.1C, this device is recommended in laboratory applications.

The temperature sensor used is LM135. It provides a voltage at its terminals (A and K) U0 = 2.73V + 10mV / degree, for a supply current of 1 mA.

In practice, there was an excellent linearity and a small variation of the voltage of 2.73V from one unit to another. The voltage with which the sensor is supplied comes from the reference voltage source, thermostabilized, made with integrated IC 2, type LM723.

The range of work being 0… 100C, a maximum voltage of 2.73V + 100grade x 10mV = 2.73V + 1.000V.

5. Tester for transformers

It presents a digital instrument with quantitative display on a bar-graph with LEDs, with which the short-circuit (or interrupted) turns of a transformer can be identified. Especially useful for testing line transformers in TV.

6. Warning relay for cars

The car warning relay (electronic) presented in the article, replaces the old electromagnetic relay designed to signal the abnormal charge of the car battery - which has as a warning element the bulb on board marked with +/- BAT, BATTERY, or with the symbol for a battery pack.

It is specified that such a relay does not indicate (by turning off the light bulb) an optimal battery charge, but signals (by turning on the light bulb), only the critical situations of non-charging or insufficient charging and excessive battery charging, the exact value of the charging voltage being monitored with the help of other on-board devices (for example with an indicator needle as in the case of the Dacia 1300).

The scheme presented in the article has as basic element the integrated circuit LM339 which comprises 4 precision voltage comparators, two by two being mounted in a comparator configuration with the hysteresis window.

With their help the voltage at the battery terminals will be compared with 4 voltage levels set by the user and depending on the output signals of the comparators, it is decided to signal or not to signal a critical situation.

7. Electrical path detector for 220Vac

The trivial application, which is based on a counter-divider with 10, respectively the integrated circuit CD4017, facilitates detection of electrical paths in the wall, which supplies various consumers at 220V.

The live wire (phase conductor) is practically detected, up to the interruption point (defect).

It is very useful for determining a cable defect, in tests (with antenna of approx. 9 cm) the accuracy of the fault point (of the phase conductor) being of the order of cm.

In the experiments performed good results were obtained for the paths embedded in the plasterboard wall. It is less sensitive to paths embedded in concrete plaster.

The LED emits 5 flashes per second, the network frequency, 50Hz being divided accordingly, the LED being mounted at the first divider output. A push-button powers the assembly from the battery connected to the two-terminal block terminal.


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