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Interesting research on ceramic capacitors

I found an interesting article about the capacitance of ceramic capacitors may depend on voltage applied. In some designs, you can face a problem when ceramic capacitor capacitance may strongly depend on voltage. Few tests were done with various capacitors using the following circuit: In the circuit CX – tested capacitor; C0 – known capacitor. Voltage vas regulated from 0 to 50V using potentiometer R1. 50V is taken as the nominal voltage of the ceramic capacitor. Because Two capacitors are connected in series the total capacitance is C=CX·C0/(CX+C0) then we find the capacitance of tested capacitor CX=CÂ·C0/(C0-C); C0 is about 10 % of CX value. There were several capacitors tested and stunning results were found. – Some of the capacitors lost capacitance from 10 to 15 times due to the increase of voltage up to 50V. Even when 10% of voltage were applied the capacitance was only about 35 – 40% of nominal value. The only explanation may be that low-quality dielectric material is used in (no-name) ceramic capacitors. Of course, not all capacitors gave the following results. But be ready for this when using unknown producer ceramic capacitors.

Understanding and calculating decibels

A decibel is a special unit that is a little different from other measuring units in everyday practices. This is a nonphysical unit but more mathematical understanding. Decibel (dB) units are similar to percent (%), just different calculations and purposes. As a percent unit, so decibels are used to compare two quantities as the whole value in percents is expressed as 100%, so decibels are more complex, and it is a ratio of two independent quantities. Decibels are mostly used for energetic parameters like power or voltage and current. Decibel (dB), equal to 0.1 bel (B) . Bel – is a decimal logarithm of the ratio of two powers. If these powers P1 and P2, then the expression looks like this:

Characteristics of sensors and transducers

A sensor or transducer is a device that converts one type of energy to another – usually electric. They are used for various purposes, including measurement or information transfer. Generally speaking, a sensor or transducer is a device that converts a signal from one to another. Let’s go through transducer characteristics that describe the performance of sensors. One of the characteristics that describe the functional relationship between physical input and electrical output is the Transfer Function, which shows the relationship between the input and output signal. Depending on the details of this characteristic, it may be a complete description of sensor characteristics. The transfer function may be used as a calibration curve. For instance, let’s take an example of the infrared temperature sensor.

RS-422 interface basics

RS-422 is a standard for serial data transfer similar to RS-232, but it uses the difference between two lines (RS-232 uses a reference to ground). RS-422 uses twisted pair (difference pair) to represent the logic level. Such data transmission type is so-called balanced transmission as it is not referenced to ground. This is a noise-proof solution because the same noise affects both lines, which are differentiated out. This allows carrying data at much longer distances at higher data transfer rates. RS-422 can transmit data to up to 1200metters. The maximum transfer rate can be 10Mbits/s. 120Ohm resistor acts as a terminal resistor that removes reflections, that may occur during transmission over long distances. Voltage levels between twisted pair lines are 4V and between transmission lines is 12V. RS-422 can be compatible with the RS-232 interface by simply connecting the negative wire of the twisted pairs to the ground.

Build your own RS232 adapter with LED indicators

After making a simple RS232 adapter, I have decided to improve it a little bit and added status LEDs of TXD and RXD lines. This adapter works with my AVR development board and should work with any TTL level UART interface. The unit is powered from the target board using power pins. The circuit: And PCB:

Simple TTL to RS232 adapter

During my spare time, I made a quick TTL design for an RS232 adapter that works with my AVR development board. This adapter helps to connect TTL (Transistor-Transistor Logic) level signals to the RS232 interface. TTL side is a 9-pin female connector, and RS232 sire is a male connector. The unit is powered from the target board using power pins. The RS232 TTL adapter circuit: Put all the in a plastic case and see what I have got:

Interfacing LCD display to 3V circuits

Usually, we are used to connecting LCDs to 5V systems. LCD controllers usually require a 5V power supply, and there must be some compliant circuitry used when interfacing to 3V systems like ARM LPC2000 microcontrollers. Here are few examples how this problem could be solved. Solution number 1 Standard LCD microcontroller can work with lowered power supply voltage to 2.7V. For this negative voltage for regulating contrast is needed. For this special inverting IC is needed or another solution. In this case, there is the ability to write and read from the LCD controller.

Place electronics parts correctly on PCB

Let’s go through a few examples of how to place electronic parts correctly on the PCB board. SMD electronic parts, especially if the lead pitch is above 1 mm, then placement of leads has to be symmetrical on copper planes: If IC has a smaller lead pitch like 0.5 – 0.8mm, positioning by hand becomes harder. Sometimes it is recommended to use special glue to fix SMD parts before soldering. DIP electronic parts must be soldered as close to the PCB board as possible to make them stand stable and avoid heat resistance.

Drive dot LED matrix display using LPT port and driver IC

It is convenient to drive dot LED matrix displays using IC drivers of 5×7 dot LED matrices like MAX6952 and MAX6953. These two IC’s differ only by data interfaces: SPI for MAX6952 and I2C for MAX6953. In this article, you will see how these driver IC’s can be controlled by a computer using an LPT port. The program provided here works with almost all Windows versions: 95, 98, 98SE, ME, NT, 2000, and XP. The printer ports that can be used are LPT1 and LPT2. The program is called MAX6952, and it is programmed by using Visual Basic 5. To start this program, you will need a few standard VB run time libraries: MSVBVM50.DLL. The program uses a freeware driver of parallel port: DriverLINXTDLPortIO.DLL, responsible for hardware I/O in win32.dll and is not accessible by standard VB. Windows NT and Windows 2000/XP require drivers too. It is DLPortIO.SYS. Both drivers are owned by Scientific Software Tools, Inc. DriverLINXT is a registered trademark of Scientific Software Tools, Inc. First of all, installation on win98. Download file MAX6952-95.exe (793kB). This is a self-extracting archive that contains ReadMe.txt, ReadMeSST.txt, MAX6952.EXE, DLPortIO.DLL, and MSVBVM50.DLL. By default install directory is C: MAX6952. File MSVBVM50.DLL can…

Endoscopy inspection in electronics-detect BGA defects

Endoscopy is known to be used in medicine, but it can also be used in other areas of industry like electronics. In big electronic industries where investments are huge, the requirements for quality are also big. In big industries, there is automatic testing using. This allows achieving maximum quality with minimal cost. In smaller industries, there is a requirement to inspect almost every product to avoid faults. One of the biggest problems that may occur is soldering errors, position errors, or other defects. For visual defect identification, endoscopy is often used. Endoscopy in electronics is some AOI (Automatic Optical Inspection), often used to check BGA pins. The endoscope usually consists of a light source directed by fibber glass and an optical sensor with variable focus. Changing focal length, it is possible to view about 50mm area while space between chip and board can be only 0.05mm. Information from the optical sensor can be sent to a computer for further processing. Comparing to the X-RAY method, optical inspection of electronic devices is cheaper.