LCS-1M - Ein einfaches, preiswertes, mikrokontrollergesteuertes Zweikanal-Oszilloskop zum Selberbauen

von Wolfgang M. (womai)

T'schuldigung, der Rest ist derzeit noch auf Englisch (mein Originalbeitrag ist auf Instructables, und auch meine - weitgehend gleichlautende - Oszilloskop-Webseite ist Englisch). Fuer Fragen und Auskuenfte zum Oszilloskop stehe ich aber gerne auf Deutsch, Englisch und noetigenfalls Franzoesisch zur Verfuegung! (email ist auf meiner Webseite, http://www.pdamusician.com/lcscope)

[Bearbeiten] Einleitung

This instructable will show you how I developed a simple yet full-featured digital sampling oscilloscope that I hope will enable you to get a successful start in this domain. The main goals in this development were:

Create something that is really usable in practice - i.e. it must have sufficient sample rate to at least cover the audio range (DC up to well over 20 kHz), and a wide input range (from Millivolts up to several Volts). The present design actually is usable up to about 150 kHz (sample rate is 1 MHz = 1 million samples per second). The maximum voltage range is -15 to +20 Volts, but can also go down into the low mV range.

Use only readily available, inexpensive parts which don't need special skills to assemble - e.g. no tiny surface mount components. The whole scope can be put together with a cheap soldering iron, a small wire cutter and flat-nosed pliers.

Keep down cost as much as possible and design it in a way that all the components are easy to procure and assemble, so any moderately skilled hobbyist can build his/her own (see circuit description later).

Make it easy to use so even a user without much experience with oscilloscope gets a quick start, and make it compact so it doesn't use much desk space.

Last but not least, make it an open design so anyone can improve upon it. Note that the design may be used without any restrictions for personal, non-commercial use only. Any other use is strictly prohibited without explicit, written permission by the author.

You can get additional information as well as download the original design files (schematic, layout) and scope software from my oscilloscope homepage. From this site you can also obtain the bare printed circuit board and the pre-programmed microcontroller.

In case you wonder what LCS-1M stands for, it's Low Cost Scope, 1 Megasample/sec.

Good luck!

Disclaimer (yes, this is a litigious world :-):

The author of these pages does not assume any responsibility whatsoever regarding the design, construction or use of the described circuit. The author cannot be held responsible for any damage to persons or property connected with the described design. This includes (but is not limited to) damage to your computer, fitness for a specific task, and specified performance. If you decide to build the oscilloscope and use it, you do so at your own risk. Observe safety guidelines when soldering, as well as when using the oscilloscope. Never apply any voltage exceeding 20V to the oscilloscope inputs.

An oscilloscope is an invaluable tool for anyone working in electronics. It allows studying electrical signals that are changing over time. Perfect for troubleshooting, monitoring, or simply observing one's electronic creations in more detail.

Unfortunately, even with significant reductions in cost in recent years, a usable oscilloscope remains out of reach for many people who could benefit from it - especially young students just starting out, and many hobbyists on a limited budget. A good low-end standalone scope easily comes in at over US$1000, and even PC-based scopes (which connect to a computer for display and control) usually cost US$300 and above.

On the other hand, most "hobby" solutions (sound-card based or purely microcontroller based) lack sufficient performance and usually are not much more than toys without much practical use. Most of the time they are more like "proof of concepts" that lack any decent frontend (to amplify small signals or attenuate signals) and have bandwidths much too low even for audio.

Of course it is often possible to pick up a decent used analog scope on Ebay for a good price, but most such scopes (cathode ray type) are rather bulky and bothersome, especially for someone without the luxury of a spacious electronics lab, and they often are difficult to use without a good dose of prior experience.

Eine Liste von Features:

Here is an overview about the capabilities of my design:

Hardware Performance:

Two independent input channels
Sample rate up to 1 MSample/sec (good enough for signals up to approx. 150 kHz)
Analog bandwidth approx. 400 kHz
Input impedance > 100 kOhm
Sensitivity from 20mV/div to 1V/div (20 vertical divisions).
Vertical offset 0 - 20 divisions (except for 0 - 12 divisions in 1V/div range)
Record length 256 samples per channel
Trigger on CH1 (rising or falling edge, selectable) or autotrigger
Connects to PC through serial port (RS-232) or USB
Power supply from a generic wall-wart type supply (9 - 15 V DC)
Compact and lightweight (about the size of a DVD box)

PC-based Scope Software:

Runs on Windows 95, 98, 2000, XP, Vista
Fully graphical interface.
All settings (timebase, vertical resolution, trigger) are controlled from the PC.
Screen update rate up to 7 frames/sec (mostly limited by scope hardware; will improve with future versions of the hardware)
Real-time Fourier transform (frequency spectrum display)
Real-time averaging
Waveform measurements using cursors
Waveform export to Excel etc. (.CSV file format)

Construction:

All components easily available and inexpensive. About half of the chips can be obtained as free samples from the manufacturer.
Total parts cost approx. US$60 for minimal version (bare board, i.e. no enclosure).
Through-hole and DIP packages only - easy to assemble and solder.
Can be built up on a breadboard or a protoboard (but I'd recommend the "real" printed circuit board to minimize work and possibility for mistakes).
No adjustments or trimmings necessary whatsoever - put it together and use it right away! Thus very beginner-friendly.
No separate programmer needed for the microcontroller (Picaxe 28X1) - the cable already used for PC connection is all that is needed. Programming software is freely available as well.
Fits in a robust standard enclosure
Accepts standard 1:1 probes, BNC cables, or grabber cables.