Conex Club Magazine - no.4 - 2003

Conex Club Magazine - no.4 - 2003 - DS18S20 - Digital temperature sensor with 1-wire bus

Reading time: 6 minute

The main topics presented

1. Electronic components for SMT (V) technology

"Fine Pitch" Capsules

For a number of terminals greater than 84, it was found that the use of capsules with a distance between terminals of 50 mil is no longer efficient and it was proposed to switch to finer capsules called "fine pitch".

The standard adopted by all VLSI circuit manufacturers in the USA is a 25 mil capsule between the centers of the gull wing terminals. Although the "J" terminal has been adopted as a standard for PLCCs, for "fine pitch" capsules the "J" terminal becomes difficult to manufacture.

Capsules with a pitch of 25 mil (0,635 mm) are referred to as EIA MO 986. Their number of pins is 84, 100, 132, 164, 196 and 244 and the body size varies between 20 mm2 and 42 mm2.

Because the capsule has a bumper at the corners that extends 2 miles above the level of the terminals to protect them during assembly, the "fine pitch" capsule is also called BQFP (Bumpered Quad Flat Pack).

The terminals are protected to the touch, these capsules can be delivered in tubes or rolls with tape. The metal version of this capsule is called BMQUAD.

Tape Automated Bonding

The concept of TAB (Tape Automated Bonding) encapsulation was originally realized as a fast and robust alternative to wire welding (Wire Bonding). Currently, TAB has proven to be a powerful method of transporting and assembling semiconductor chips on the printed circuit board.

To achieve TAB, a set of conductive paths is created on a support band through a photolithographic process. The network of conductive paths in the form of slats corresponds to the pills of the unencapsulated integrated circuit (chip).

The connection of the chip is made in a single operation, usually by thermocompression. After gluing, the faces are encapsulated in the resin, see figure 14 (from the article)

The chips can be kept in this shape, the tape ensuring the robustness of the structure. For assembly, the tape is placed on the printed circuit board, the outer area of ​​the slats is cut and removed and the remaining ends are glued to the pads on the printed circuit board.

Capsule Ball Grid Array - BGA

The use of the BGA capsule has been demanded by the problems that appear in the use of "fine pitch" components with a large number of terminals that pose difficult handling problems.

Also, depositing the solder paste to such dimensions is a difficult operation. BGA capsules have robust ball terminals, and the pitch is significantly higher.

Usually, the introduction of a new family of capsules with a higher packaging density is accompanied by a reduction in yield and quality, as was the case with "fine pitch" and TAB.

The BGA case is an exception, the capsule ensuring a high density with increasing yield. The BGA capsule is derived from the PGA (Pin Grid Array) capsule, but instead of pins it has solder balls.

Chip Scale Package capsules

A capsule that occupies only 20% more of the size of the semiconductor chip is called CSP - Chip Scale Package. CSP capsules offer a higher packing density than BGA but lower than flip chip.

The advantage of CSP is that the technological process is not as complex as that for the flip chip (C4 process), but is compatible with the processes in surface mount technology.

2. Timer with microcontroller

Made with the microcontroller AT 90S1200, the application offers maximum timings of 99 minutes and 59 seconds, programmable.

The assembly is a timer based on the AT 90S1200 microcontroller (AVR type) and which is structured, from a constructive point of view, on two printed circuits interconnected by the K9-K10 connector (figure 1 in the article).

The time base is piloted by a quartz crystal with a frequency of 4,096MHz. The display is multiplexed on a 4-digit display (IC4) controlled on the segment inputs by a microcontroller (IC1) and on the cathodes of the buffer IC2. Circuit IC2 also controls relay REL1.

3. Mains voltmeter for PC - with timed overvoltage protection

Measuring devices displayed on the personal computer monitor tend to develop rapidly nowadays for several reasons: from an economic point of view, decreases the cost of the device by removing the display with LCD liquid crystals, which is an expensive component and with limited display possibilities in terms of the number of characters and the color palette offered;

From a functional point of view, the computer allows the implementation of several measurement functions, complicated mathematical calculations can be performed in short time intervals, measured values ​​can be recorded and stored, etc.

The design time also decreases, the graphical programming environments allowing both the fast configuration of the graphical interfaces, and the realization of the complex mathematical functions. by using powerful instructions, resulting in compact program codes.

The mains voltmeter presented in this article performs both the voltage measurement function and the overvoltage protection function, with a timer set by the user.

The connection to the computer is made through the serial port. The graphical interface is made in the Visual Basic - VB6 graphical programming environment. The electrical diagram of the hardware part is presented in figure 1 (from the article).

It is organized around an industrial microcontroller from the AVR series, AT9054433-8PI, which also contains the digital analog converter (with successive approximations) necessary for the measurement process. The voltage reference of the ADC has the value of + 5Vdc and is taken from the power supply of the microcontroller through the low-pass filter R4-05. The converter is 10 bits with 8 channels.

4. DS18S20 - Digital temperature sensor with 1-wire bus

The DS18S20 circuit produced by Dallas Semiconductor & Maxim performs the function of a 9-bit digital thermometer. The measured temperature value is transmitted on a Microwire (1-Wire) bus for communication with a microprocessor, for example.

The circuit also has the alarm function, its thresholds (bottom and top) are set by user software and stored in a non-volatile memory.

Several DS18S20 circuits can operate on the data line simultaneously. The circuit has a unique 64-bit code for identification. Among the applications we mention: monitoring the temperatures inside buildings, machines and industrial equipment, monitoring the processes and controlling the systems.

Technical data:

  • measured temperature range: -55C… + 125C;
  • accuracy +/- 0.5 ° C in the range -10C… + 85C;
  • 9-bit resolution;
  • conversion speed: max. 750ms;
  • 1-Wire bus for communication;
  • 64-bit unique identification code (ID);
  • alarm thresholds set by the user in non-volatile memory.

5. Network PC thermometer with DS18B20

Create a PC interface to measure temperatures in the range -55… + 100C with good accuracy, it seems a trivial thing to many designers.

The problem occurs when you want to measure at a distance, at various points, at more than 100m. The solution comes from the "MicroLAN" technology that allows the sharing on a "1-Wire" bus of several components, without affecting the measurement result.

The installation we present is a direct application of the D18B20 circuit, respectively a temperature measuring interface for PC (virtual instrument).

The interface connects to the COM1 or COM2 port of the PC (RS232). The wiring diagram (figure 1 in the article) is very simple - converter RS 232 / TTL with CD4007.

The two port signals Rx and Tx are "gathered" on a single wire (to the ground) - the 1-Wire bus and communicates with DS18B20 at pin DQ (2).

The supply of the CD4007 circuit is made from the port by rectification, filtration and stabilization at + 5V (with LM2931A) of signals from the port (DCD, DTR and DSR).

6. STK402-xxx

The STK402-XXX series of hybrid audio integrated circuits is produced by SANYO in technology IMST (Insulated Metal Substrate Technology) which allows to reduce by about 60% the thermal resistance of the substrate (compared to the old STK407 series), which led to the miniaturization of the capsules.

  • from 15W / channel to 40W / channel (THD = 0.4%): 46,6X25,5X8,5mm;
  • from 50W / channel to 80W / channel (THD = 0.4%): 59,2X31X8,5mm.
  • The rated load impedance is 6 Ohm.

The same printed circuit board can be used for the entire series (starting from 20W to 120W per channel), the integrated circuits being compatible pin to pin.

In table 1 (from the article) the output powers (at 0.4% total harmonic distortions, in the band 20Hz… 20KHz) for the whole series are rendered, together with the supply voltages recommended by the manufacturer.

7. Electronic ignition - For petrol engines

The electronic assembly shown is a fully transistorized electronic ignition for combustion engines that use gasoline fuel.

Electronic ignition offers multiple advantages, the manufacturers of the new cars already including it in the equipment of the new models.

The advantages are:

  • better start;
  • less polluting smoke;
  • petrol economy;
  • better engine performance, especially at very high or very low running speeds;
  • less (even visible) wear of the breaker (platinum contact).
  • switched current: 4A;
  • switching frequency: up to 500KHz;
  • average ignition time (typical): 2ms.

8. Fast 3-bit A / D converter

The application presented is known as parallel converter.

An important factor in data acquisition is the conversion delays that come from a complex scheme in the generating chain between the saw, comparator, counter or oscillator.

In the case of the scheme presented in the article, the delay is small, so the whole conversion process is very fast. The disadvantage of the method is the large number of components, because each conversion step requires a comparator, which in the diagram shown - three-bit conversion - is not a special problem.

The comparators used are of the type LM324. Their threshold voltages are provided by an LM7805 type regulator, which offers + 5V by division with precision resistors of +/- 1%.

The fixed reference voltage (+ 5V) is applied to the reversing inputs of the three comparators. The analog input signal is applied to the non-inverting inputs of the comparators. Their outputs are coupled to the two non-inverting buffers coupled in parallel.


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