Homepage of Stefan Salewski
Digital Storage Oscilloscope (DSO)
One of my current projects is the design of a little box which is connected to a PC or Notebook computer by USB and can be used as a Digital Storage Oscilloscope. (My own internal naming is Data Acquisition Device (DAD) because I am more interested in data acquisition in scientific area than in monitoring electrical signals. Basically it is the same, but for data acquisition more memory is useful and more than 8 bit accuracy may be desired.) Of course such devices are available from different vendors for some years now, so why build another one? Well, there is no device available which provides all its software in free, open sourced form, or which provides at least full schematics. Many devices are "Windows only" too. And of course it's a lot of fun designing such a device.
Some (intended) features for the first prototype
- Two fast analog to digital converters with 12 bit resolution
- Analog bandwidth (-3 dB) above 100 MHz
- Sampling rate up to 100 million samples per second (MSPS) for both channels,
- 200 MSPS for single channel operation and
- even higher resolution for periodic signals employing Equivalent Time Sampling (ETS) also called Random-Sampling or Postcorrelated Undersampling
- Input range: 50 mVpp up to 200 Vpp full scale (1MOhn/35pF)
- 4 single ended digital inputs with BNC connectors
- 16 inputs supports single ended or differential digital signals
- Input range for digital signals is -4 to +5V with adjustable threshold
- Analog (Channel 1 only) and digital trigger
- External trigger and external clock is supported
- One digital signal output (BNC, 3.3V) and one switch output (relay)
- One analog output for arbitrary slow varying signals in the range from -5 to +5V
- Fast onboard memory for more than 512k samples (2 Megabytes total)
- USB (full speed) and RS-232 (mainly for debugging) connection to PC
- Power supply: USB supported by Li-Ion-Accu, wall plug (5 to 32V) for long time measurements.
Of course it's a non trivial, long term effort, maybe never finished. And please do not expect that such an open, "do it yourself" device can be cheaper than similar commercial ones. It is not as long as we build it only in small quantities.
The schematics are nearly finished now -- here is the latest snapshot in PDF format:
And single sheet version:- Overview.pdf
- InputDividerCh1.pdf
- InputDividerCh2.pdf
- AmplifierCh1.pdf
- AmplifierCh2.pdf
- AmpCommon.pdf
- TDC.pdf
- PowerManager.pdf
- DC_DC_Converter.pdf
- Digital_In_A.pdf
- Digital_In_B.pdf
- Digital_In_C.pdf
- Controller.pdf
- ADC.pdf
- FPGA_Power.pdf
- FPGA_B0B1.pdf
- FPGA_B2B3.pdf
- Misc.pdf
- Lin_Regulators.pdf
- RAM.pdf
- Grounding.pdf
Schematics are drawn with gschem, the schematics editor of the free, open-sourced gEDA project (GPL'd suite of Electronic Design Automation tools), see www.gpleda.org. Special schematic symbols not included in the gEDA package are available from my sub-page at www.gedasymbols.org for free download.
My (long term) intention is to build some prototypes with basic, free and open-sourced software (GPL). (As you may know, my GPL USB firmware for the AT90USB1287 is already available since some years.)
Here is a picture of the current status of the PCB board...
And the PCB file, compressed with bzip2. (Nearly finished).
And finally a snapshot of my working directory, with schematics, pcb board, symbols and footprints:
Recently I started working on a GTK+ GUI for this hardware. Here is a screenshot of an early draft:
Please note: Currently all schematics are copyright by the author -- I will not worry about a appropriate free license for this project (GPL is not well suited for hardware) before I have at least a working prototype, or before other people will join this project.
My draft of a simple and cheap analog input stage for a DSO is available here:
And finally a recent sketch of an input stage for higher bandwidth, which needs only two HF relays for signal selection: