An oscilloscope (often abbreviated o'scope or scope) displays signal voltages as a 2-D graph, usually as voltage (vertical axis) as a function of time (horizontal axis).
The o'scope is one of the most important pieces of test equipment because it lets you look at what is happening in different parts of a circuit. Without it you are almost blind ( multimeters and logic analyzers can also help you "see" ).
The probe of a o'scope is held against, or is clipped to, the metal wire carrying the signal of interest.
A dual-trace o'scope has 2 probes, so 2 different signals can be seen -- so not only the shape of the signal can be seen, but also the exact time from events on one signal to events on the other signal.
Sometimes one wants to look at a 8-bit data bus -- typically one uses a "logic analyzer" to look at lots of time-aligned digital signals. For a given number of signals to look at, oscilloscopes (which show the true analog waveform) are much more expensive than logic analyzers (which only show if a digital waveform is hi or low, above or below the logic threshold). Many people buy both a (dual-trace) o'scope and a 16-trace logic analyzer, which together have a total cost less than one true 8-trace o'scope.
... more techniques ...
Open Source Oscilloscopes
Of course, you have to already have a working o'scope in order to build and test another o'scope, making this the same sort of chicken-and-egg problem as the RepRap project, the GCC project, and other projects David Cary finds interesting.
Open Hardware for PC Oscilloscopes
- $575 BS100U: 2 analog inputs + 8 digital inputs, optically isolated, from BitScope Designs (MetaChip Pty. Ltd.) ; review by Endolith
- $695 BS325U: 2 analog inputs + 8 digital inputs, optically isolated, from BitScope Designs (MetaChip Pty. Ltd.) 
- $1595 BS442: 4 analog inputs + 8 digital inputs, ethernet connection, from BitScope Designs (MetaChip Pty. Ltd.) 
- $475 BS50U: 1 BNC analog input + POD (2 analog or 8 digital inputs), usb powered, from BitScope Designs (MetaChip Pty. Ltd.) 
Some people on the PIClist have been discussing designing an open-source oscilloscope.
- I think initial discussions occured on the "[EE scope project anyone?"] thread  at PIClist.
- Later discussion moved to the "MultiAnalyser" group at Yahoo
XMEGA Xmegalab Development Kit and Oscilloscope
- $249 The Xmegalab is a development board for AVR XMEGA microcontrollers, a dual channel oscilloscope, an arbitrary waveform generator and a scientific calculator. Xmegalab. Alpha version of the firmware (mostly in C) has been released under the GPL. Serial port; SD Card with FAT File System support, etc.
Xprotolab - Miniature Oscilloscope and Waveform Generator
- $35 The Xprotolab is a small mixed signal oscilloscope in a DIP module, designed to be used on a breadboard. It also has an arbitrary waveform generator. Xprotolab.
Closed, COTS Hardware for PC Oscilloscopes
- For low frequencies, pretty much any external sound card with a line input will work. External card line inputs generally have a range around 0-1 V whereas onboard microphone inputs only have up to about 50 mV, which just isn't enough sensitivity. The Virginia Tech Lab-in-a-Box recommends the Behringer UCA202. To use a sound card oscilloscope on a regular basis, a circuit with variable attenuation is recommended (i.e. 1x and 10x). Compensation for the hardware and software gain can be done as part of the attenuator circuit or in software.
PC Oscilloscope Software
- Sourceforge: xoscope is a digital oscilloscope for Linux that uses input from a sound card or EsounD and/or a ProbeScope/osziFOX and will soon support Bitscope hardware. The sound card device is hard-coded but instructions for modifying it are on the VTLUUG wiki.
- Baudline GPL version is a signal analyzer designed for scientific visualization, using input from recorded data files or from a sound card. For Linux / Solaris. The source code is expensive and it is intended for qualified corporate or institutional buyers.
- Miniscope v3 is a digital oscilloscope for Windows. It connects to device using external dll. Available libraries to connect with sound card, Microchip MCHPUSB Generic HID Demo and custom AT91SAM7S64 hardware.
- Digital Soda is a simple GTK+ frontend for the DSO-2250 USB oscilloscope for Unix/Linux.
- Osqoop is an open source software oscilloscope. Osqoop project features an arbitrary number of channels and long acquisition durations. Signal processing and external peripherals control is possible through a plugin architecture.
- oscilloscope pic microcontroller demo oscilloscope PC based oscilloscope embedded system parallel port LPT.
- ArduinoScope Oscilloscope based on Arduino hardware platform and Processing library. Please look at this article(sorry it's in french)
- "Multi-Instrument"converts a PC into multiple test & measurement instruments such as oscilloscope, spectrum analyzer, signal generator, spectrogram, distortion analyzer, network analyzer, data logger, LCR meter, vibrometer, etc. Besides sound cards, it supports many other ADC/DAC cards. Free Trial with full functionality for 21 days.
- Baudline gratis download (dual licensed, see Free Software entry).
- Zelscope Converts your PC into a dual-trace storage oscilloscope and spectrum analyzer. It uses your computer's sound card as analog-to-digital converter. Windows trialware.
- BitScope DSO is a digital oscilloscope logic analyzer for Linux and Windows. It works with BitScope hardware and is distributed as freeware.
- Zeitnitz Souncard Scope and function generator. For Windows but runs under Wine.
Non-PC Oscilloscope Projects
- "Handheld Multifunction Scope" by Jingxi Zhang & Yang Zhang, 2007. "dual-channel oscilloscope supports 250 ksps for each channel". ... also: ohmmeter, capacitance meter, and inductance meter ... pulse generator ... small speaker and OLED output. All functions work stand-alone with OLED display, but it can also be to a host PC with the USB port to display waveforms on the PC display.
- Dan's Workshop: Notes on converting that old compact tv set or computer monitor into an oscilloscope.
- "TV Oscilloscope Adaptor" "This ... adapter ... changes a TV to a Oscilloscope."
- Some people are discussing the possibility of somehow converting the (open-source) uWatch into a o'scope: WBL: watch based laboratory
- Poor Man's Digital Oscilloscope
- K3PTO http://www.qsl.net/k3pto/ 8 bit
- Massmind: "SX based O’Scope" by Alberto Geraci of BTX Sistemas
- "PIC12F675 Oscilloscope"
- "DIY HACK - Make your own Oscilloscope"
- "Solid State Oscilloscope" by George Katz 1987 -- an extremely simple and small circuit that drives a 10 x 10 LED array. (Would it make sense to adapt the PointLess LED Array to be more like this?)
- "The µSCOPE: A poorman's oscilloscope" by Ronald Dekker. An extremely small and low-cost circuit based on the 8 pin Microchip PIC12f675; displays "signals up to a few kHz" on a PAL TV screen. "isochronous code".
Epanorama has many links related to o'scopes and o'scope accessories .
Oscilloscope Design Discussions
some low-cost oscilloscopes
some low-cost oscilloscopes, in no particular order. ... it would be nice to mention sampling rate, # of analog input channels, # of digital input channels, whether it can be used under Linux, does it have output channels ... price should (?) include 2 analog probes, ... is it open hardware? ... anything else?
- price name comments
- $50 JYETECH Oscilloscope and frequency counter, 1 input, 1MHz analog bandwidth, LCD screen, serial port screen capture  available here: 
- $50 Usbscope.eu, low cost 2 channel (4 channels available soon), 40 kHz sample rate, 10 bit, 200 samples/channel. 
- $150 (?) VELLEMAN HPS10 Hand Held Oscilloscope 10MHz sampling rate, LCD: 128x64 pixels 
- $349.95 VT DSO-2815H,1x150MHz or 2x75MHz,sophisticated trigger functions, a wide range of gain selection, 1kHz squarewave output, with a Multi-Instrument Standard software license, which converts a PC into oscilloscope, spectrum analyzer, multimeter, signal generator, data logger...it also supports sound card (both MME driver and ASIO driver), NI DAQmx cards, etc.  The software can be downloaded for 21-day fully functional trial with at least sound card at 
- $299.95 VT DSO-2810H,1x100MHz or 2x50MHz,sophisticated trigger functions, a wide range of gain selection, 1kHz squarewave output, with a Multi-Instrument Standard software license, which converts a PC into oscilloscope, spectrum analyzer, multimeter, signal generator, data logger...it also supports sound card (both MME driver and ASIO driver), NI DAQmx cards, etc.  The software can be downloaded for 21-day fully functional trial with at least sound card at 
- $250 VT DSO-2810F,2x100MHz, with a Multi-Instrument Standard software license, which converts a PC into oscilloscope, spectrum analyzer, multimeter, signal generator, data logger...it also supports sound card (both MME driver and ASIO driver), NI DAQmx cards, etc.  The software can be downloaded for 21-day fully functional trial with at least sound card at 
- $89 Poscope Basic2 from PoLabs PoLabs, 2 analog channels, 16/8 digital channels, PC USB oscilloscope, spectrum analyzer, chart recorder, pattern generator, logic analyzer, PWM/ square generator
- $139 Poscope Mega1 from PoLabs PoLabs, 2 analog channels, 16/8 digital channels, PC USB oscilloscope, spectrum analyzer, chart recorder, pattern generator, logic analyzer, PWM/ square generator
- $206/$328 PicoScope 2104 and 2105, 1 channel handheld oscilloscopes from Pico Technology 
- $262/$371/$387 PicoScope 2200 range from Pico Technology, 2 channels, 1 output 
- $667/$1002/$1332 PicoScope 3200 range from Pico Technology, 2 channels, 1 output 
- $823 PicoScope 4224 from Pico Technology: 2x80 MS/s, 12 bit, 20Mhz BW, 2 input channels, includes 2 X1/X10 probes, USB cable, and carrying case. USB powered. 
- $200 Hantek DSO-2090 USB PC Oscilloscope 
- $380.00 DSO2250 100MHz PC-SCOPE 250MS/s 
- (about US$400.00) GAO2250 100MHz 250MS/s USB PC Oscilloscope, Gaotek Inc. A Canadian source for the DSO-2250. 2 input channels plus trigger. Provision for ground and calibration. Windows only, AFAIK, no Linux. Gao's latest website doesn't quote a price, but when I got mine it came to about CAN$500, including US conversion and Canadian taxes. 
- CAN 219.99 Syscomp Electronic Design DSO-101  (Syscomp supports the "The Open Instrumentation Project" )
- EUR 427 ETC s.r.o. M520 Oscilloscope 
- $222 ANT8 : 8 Channel Logic Analyzer (EasySync)
- $200 PS40M10 : Swordfish Hand-Held Instrument (1 channel) USB (EasySync)
- $220 DS1M12 : Stingray Multi-Function Instrument (2 channel) USB (EasySync)
- under $600 : Jameco has some actual stand-alone oscilloscopes for under $600. So does www.tequipment.com - see Rigol 'scopes from China - good quality - also on eBay.
- under $200 : Carl's Electronics has some stand-alone and PC-hosted (parallel port?) oscilloscopes for under $200.
- $170 HobbyLab USB oscilloscope 
- $500 DS1022C : 2 Channel, 25 MHz Rigol Technologies Inc.
- $999 CS320A Cleverscope  (has a discussion forum)
- $167 DrDAQ "data logger" (parallel port) from Pico Technology 
- $970 NI USB-5132 : USB digitizer from National Instruments 
- $139 Parallax USB Oscilloscope 2 analog inputs + trigger; 1 MS/s 
- $170 PC USB Oscilloscope DiSco (HobbyLab, LLC). 2 analog inputs ( 200 KHz ) + 16 digital inputs (or 8 digital inputs + 8 digital outputs). 
- $150 ST16B 10 MHz stand-alone oscilloscope, 2 analog inputs 
- $190 VEPCS100 ( PCS100 ) - PC Based Oscilloscope; 1 analog input ( 12 MHz ); optically isolated from PC 
- $950 DSO-8502 USB Oscilloscope, 2 analog inputs (250MSa/s) + external trigger; 1 digital output (trigger out); buffer: 512K points/ch.
- $799 DSO-8202 USB Oscilloscope, 2 analog inputs (200MSa/s) + external trigger; 1 digital output (trigger out); buffer: 128K points/ch.
- $108 LabJack U3 USB data acquisition and control device, 16 analog inputs ( 12 bit, 2.5 KSa/s at 12 bit resolution, 50 KSa/s at 8 bit resolution), buffer: 984 samples, 2 analog outputs, digital outputs 
- $249 S2X100 USB Oscillloscope, 2 analog inputs (100Ms/s) with 8 bit resolution, buffer: 64K samples 
- $495 ELAB-080 
- $745 USBee AX-Plus, 2 analog inputs (Max 16 MS/s ?) and 8 digital inputs 
- $90 DSO nano, 1 analog input (1 Ms/s) with 12 bit resolution; buffer: 4096 Point; waveform storage on SD card ; review by Justblair
- $249 MSO-19, 1 ch. 2GSa/s oscilloscope, 8 ch. 200MSa/s logic analyzer, 100MSa/s pattern generator and a TDR. MSO-19
FIXME: Measurement Computing has some wireless and USB analog DAQ instruments -- add to the above list.
FIXME: DATAQ Instruments, Inc. has some USB and Ethernet analog DAQ instruments -- add to the above list.
FIXME: Link Instruments Inc. has several USB o'scopes and "USB MSO" ("mixed signal o'scope"). Are they already listed above?
EasySync is a distributor of RockyLogic's ANT8/etc products.
Test Equipment Solutions Today, Inc. is a distributor of Rigol's DVM and oscilloscope products.
When you search eBay for oscilloscope, you might find some good deals.
- "Scoping out palm-sized USB oscilloscopes" by Jack Ganssle 2005, Embedded Systems Design. A review of 3 USB oscilloscopes -- reader comments at the end mention a few more USB o'scopes. (FIXME: make sure all the scopes mentioned are included on the above list)
- Keith has made a list of "PC USB logic analyzers that cost under $1000.", some of which can be used as an o'scope. Should I use the same $1000 price cut-off for the above list? Or perhaps double or halve it?
- The David at "davr.org" has made a list of "PC-based Logic Analyzers under $500"
- "low cost or DIY buildable logic analyzer" discussion at chiphacker.
- "Opinions on an oscilloscope suitable for hobby electronics on a budget" discussion at Electronics StackExchange (formerly chiphacker)
- "Oscilloscope Tutorial" videos at Afrotech
- Brooke Clarke has posted a list of "PC based Oscilloscopes"
- Wikipedia: oscilloscope
- Other discussions of "Cheap digital storage oscilloscope"
- The Ganssle Group reviews Inexpensive USB Scopes and Logic Analyzers
- Massmind: Tools lists a few sources for a variety of tools used in electronics: o'scopes, logic analyzers, meters, waveform generators, etc.
- Slashdot: "Cheap PC Oscilloscopes - Any Recommendations?"
- Slashdot: "Building a Cheap Oscilloscope Using Your PC?"
- "Digital oscilloscopes for hobbyists comparison"
- ePanorama.net: "Using PC as a measurement instrument" (FIXME: anything we should add to the above list?)
- General Radio Scopes A bit of history.