Electronics FAQ

We have all used InfraRed based remotes to control various appliances around our house. All these remote work by transmitting data in form of flashes of infrared light - and wherever one needs to transmit data, there is always a protocol involved. The RC-5 protocol from Philips has been used in TVs, VCRs and other appliances since the past three decades. It was developed by Philips but was adopted by many other manufacturers. Now days RC-5 has been superseded by RC-6 and various other protocols from various other manufacturers. These newer protocols have better features and are more flexible. San Bergmans's KnowledgeBase on Consumer IR is a nice place to lookup information (protocol specs, circuits, embedded code) on any of the old or new IR based protocols. Here is how a RC-5 TV remote control transmitter unit looks like: And here is a InfraRed receiver/demodulator: A RC-5 codeword is 14 bit long. The first two are the start bits, then comes the toggle bit and finally the 5 bits ...

I²S stands for Inter Integrated Sound and is similar to the I²C which is used for transmitting data between Chips on a circuit board. ( wikipedia article on I²S). I²S is used for connecting digital audio devices together, (for example between the main processor and the audio codec chip on cell phones or computers or between the CD transport and the DAC in a CD player). I2S interface consists of at least 3 signals: Clock Left right clock Data line The eKA8562A Chip which is a USB Audio Controller (and can be used as an oscilloscope ) sports an I²S interface. Here are a few signals captured at the various pins (I²S output) on this chip: Pin 5 of eKA8562A - I²S BCLK Output Clock - This signal is used as the clock to latch in the bits appearing on the data line. Pin 6 of eKA8562A - I²S LRCLK Output Left Right Clock - This signal is used to tell the receiving devi...

Enterprising undergrad engineering students can achieve a lot if given the right set of tools. Once you level up to designing some complex circuits, a signal generator and an oscilloscope would definitely go a long way in helping you in debugging your projects. I bought my first oscilloscope ( Acute DS1202 200MHz PC based) for INR 37,500 after accumulating my salary for 4 months at my first job. But I always wished I has an access to an oscilloscope as a student. It seems that now days there is a low cost option for students to use: the PCs sound card. Most modern motherboards have an onboard Audio Codec Chip which is used to accept and output sound, you can find atleast 3 audio jacks labeled Microphone, Line In and Line Out on the back side of your CPU Cabinet. You can then use specialized freeware/shareware applications which can turn your PC into an Oscilloscope/Signal Generator. Here are screen shots of some of these: Oscilloscope 2.51 (aka Winscope) - the captured wavefor...

Bring a GSM cellphone near some low grade audio equipment and you can hear some very irritating noises. GSM or Global System for Mobiles uses FDMA, TDMA and SDMA for providing network access to multiple users. This each achieves as follows: Base Transceiver Stations within Cells (a fundamental unit of geographical areacovered by the GSM service provider) surrounding a given cell will all use frequencies different from each other (Frequency Division Multiple Access). The maximum amount of power transmitted by BTS as well as mobile units within a given cell is limited and so cells separated by a considerable geographical area can both reuse the same frequency for transmission (Space Division Multiple Access). And finally within a given cell, mobile units will use Time Division Multiple Access so that man users can be served by the same Base Transceiver Station. Of course different frequencies are used for uplink and downlink. Depending on the country, GSM operates in 800MHz to 900MHz or...

Visha Electronics carries a very low cost FM transmitter kit based around BF494 NPN Bipolar Junction Transistor. The kit has a condenser microphone to pickup sound. A variable capacitor is also present to tune the transmission frequency anywhere in the 88-108 MHz range. The transmitted signals can be picked up by any stand radio receiver. A simple receiver circuit can also be built, like the one shown here . Please visit http://www.vishaworld.com for details on more such kits. Students are invited for workshops/courses at our LARE Learning Center for an opportunity to assemble and experiment with such kits.

SPI is a serial link standard used between chips. Now days most microcontrollers have an on board SPI block. SPI link is made of atleast one master and one slave. The link is composed of four wires: SCLK - Serial Clock, always provided by the Master MOSI - Master Out Slave In, Data (from master to slave) MISO - Master In Slave Out, Data (from slave to master, clock still has to be provided by master) nSS - Slave Select, usually the Chip Select signal for the slave. Sensors, ADC/DAC, memory and many other devices had slave SPI interfaces. Some examples of SPI compatible ICs/Devices:- Accelerometers (ADIS16201) 4-20mA current control (AD420) Flash Memory (EN25T80) Nokia 6610 Colour Graphical STN LCD (PCF8833) Nokia 3310 Monochrome Graphical LCD (PCD8544) EEPROM (25AA640) SD Card 10BASET Ethernet Controller (ENC28J60) Many microcontrollers - like AT89S52 and all the AVR devices available from Atmel - are programmed via SPI. Here is a screen shot of SPI signals captured...

Here are some photos and waveforms from a PSK generation lab practicals. All undergraduate students pursuing engineering in electronics and its allied fields get a chance to do it at least once during their four years. The process of PSK generation in a lab is as follows: Generate a sinusoidal carrier wave from a signal generator. Call it Signal A Use an operational amplifier to shift the phase of Signal A by a fixed amount : usually 90 degrees in case of Binay Phase Shift Keying. Call this Signal B. Apply Signal A and Signal B to the two inputs of a 2:1 analog multiplexer. Apply the data signal to the select line of the analog switch. The output of the analog switch will be the required PSK signal. The data signal is a simple digital signal with two states 1 and 0 i.e. 0 and +5V. This can be emulated using a 555 Timer wired to generate a simple square wave. The analog switch will select Signal A or Signal B depending on the logic level of this data signal thereby outputting a sine wav...