Remember a the time before oscilloscopes had a brain? It’s easy to forget as we’ve become accustomed to a class of simple solid state oscilloscope using a microcontroller as signal processor and a small LCD display to show the resulting waveforms. They are commonly available as inexpensive kits, and while their bandwidth is not huge they give a good account of themselves in low frequency applications. But of course, originally the signal processing was handled in a much simpler way.

[SimpleTronic] reminds us that a small solid state oscilloscope does not need a microcontroller, with a ‘scope on a breadboard that displays waveforms on an LED matrix in a much more traditional manner. This is very much an analogue oscilloscope, in which the X deflection circuitry of the CRT is replaced by a decade counter stepping through the columns of LEDs on the display, and the Y deflection circuitry by some analogue signal conditioning followed by an LM3914 bar graph display chip driving the display rows. There are a few refinements such as a trigger circuit, but it remains a very understandable and surprisingly simple device.

It has a claimed bandwidth of 40 kHz defined by its sweep ranges rather than its analogue bandwidth, and an input voltage range from 50 mVpp to 50 Vpp. It’s hardly a useful instrument due to its low bandwidth, but its strength lies in novelty and in understanding a traditional oscilloscope rather than in its utility. You can see it in action in the video we’ve placed below the break.

‘Scopes of limited use appear from time to time on these pages. A favourite of ours is this soldering iron.

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