Electronics FAQ

The other day, I captured the composite video signal coming out from an infotainment device. The device had a setting which allows you to select encoding for the output signal. By setting the device to output a particular image on the composite video RCA connector (hence the waveform shown below are of unmodulated baseband video signals) and switching the device between NTSC and PAL, I was able to capture and analyse various aspects of the two standards. Test Pattern  Here is the test pattern I used. I loaded the JPEG onto a USB flash drive and connected it to the infotainment device. The device was put in image playback mode and the selected file was rendered on the LCD display as well as output on the composite video out. The image is composed of exactly 640 x 480 pixels which corresponds to an aspect ratio of 4:3. Test Pattern A short table of differences between the two standards NTSC PAL Stands for National Te...

Here is a video of a PWM signals generated using a microcontroller. The two signals are in quadrature phase - i.e. their phase difference is 1/4 of their period (or you can say they are 90 degrees apart). The signals were generated using an ATmega32. Program was written in Assembly Language. AVRStudio4 and STK500 were used as development tools.

So the waveform collection wouldnt be complete without the 50Hz AC Mains . Since the oscilloscope I am currently using is USB powered PC based, it can't handle high voltages such as the 230 Volts AC/Hz available in India. So I stuck my probes onto the secondary of a AC/DC step down adapter.. ..connected the oscilloscope to my laptop and observed the waveform and more specifically, its frequency: Just to be safe, I operated the laptop on battery and disconnected the laptop charger from the mains. Next I loaded the AC/DC adapter with a 47 ohms resistor... .. and observed the signal (note the distortion): If you are wondering if (and why) the utility frequency ever changes then the following articles would interest you: Wikipedia article on "Utility Frequency" Increase AC mains frequency? Accuracy and stability of the 50 Hz mains frequency

Waveforms of signal on a 10 Mbps Ethernet CAT5 cable (captured differentially on the RX+ and RX- wires): For the info regarding how I managed to captured this waveform have a look at the usenet discussion here and the supporting info here . Click on the image below to know how I forced my network card to operate in 10 Mbps mode only:

Whenever we press the keys on our touchtone landline phones, it transmits two sine waves simultaneously. The interface at your telephone exchange recognizes the frequencies of both of these waves and hence identifies the key pressed. This is known as Dual-tone multi-frequency signaling . The various combinations of the frequencies of each of the keys are as below: DTMF Frequencies in Hertz       KEY  FREQ1    FREQ2         1    697    1209 2    697    1336 3    697    1477 A    697    1633         4    770    1209 5    770    1336 6    770    1477 B    770    1633         7    852  ...

Here is a printout of screen capture of A and B signals of an RS485 Bus as captured on an oscilloscope (Agilent 54621A). The RS485 Bus usually consists of a twisted pair cable connected to an RS485 Transceiver. In the case, below, a twisted pair cable has not been used - the signals were directly observed at the A and B pins of DS75176 loaded by a 120 ohm resistor and biased by two 560 ohm resistors. The bus is bein operated in half-duplex mode. DS75176 (which is equivalent to MAX485 ) was connected to the UART of Atmega8 AVR Microcontroller. The data being transmitted were the characters: 'a' '0' '1' '2' 'K' 'Q' - in that order. The UART frame format is 8-N-1 and the baud rate is 38.4 kbps. The signals A and B were captured on two different channels both referenced to the common system ground. This waveform was captured while me and my classmates were working on our final year project at the end of our undergraduate engineering cour...

How to observe Spectrograms of various signals or latest pop/techno songs: Buy a Nokia phone - specially the ones like Nokia 5800 or Nokia X6 or any other which are labelled "comes with music" or "music unlimited" Install the nokia support software on your computer - especially the Ovi Player Validate your music coupon and download a few songs from using Ovi Player. This is completely legal. Install Winamp 2.95 (older version). You can get it from oldversion.com here . Start Winamp, go to preferences, set the visualization plug-in to "Spectrum Analyzer + Voiceprint" which is present in the "Nullsoft Tiny Fullscreen 2001" Library Load the song in winamp, play it and press "Ctrl+Shift+K" to watch the live spectrogram of the song. The Spectrogram is updated from left to right. Press "Esc" key to get out of fullscreen mode. If you want to see the voiceprint of your voice, "add a URL" to playlist and type ...

Here's a GIF Animation of the modulating signal (top) and the corresponding frequency modulated signal (bottom) captured on an analog Cathode Ray Oscilloscope. The modulating signal is a very low frequency sine wave fed from signal generator to an ICL8038 FSK trainer kit. You can see the frequency of the carrier wave change as the voltage level of the modulating signal changes slowly. The video was shot using a digital camera. The location is VESIT, Mumbai's Communications Laboratory. Here's how the GIF animation was created on a Windows based PC using free tools: The video was originally in .MOV (Quicktime) format. It was converted to uncompressed AVI using Rad Tools (free version of QuickTime must be installed on your system before you can convert the MOV to AVI). The uncompressed AVI was then loaded into VirtualDub and Image Sequence of a selected duration of video was exported. This particular time period of the video consisted of a seque...

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...