Seeing the Signals (& BitScope BS10, first impressions)

tl;dr

The BitScope BS10 and associated software makes a useable but basic scope, but its real potential is probably in its other facilities: simple data acquisition across various platforms (including Raspberry Pi) and the ability to monitor logic levels alongside analog signals.

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Trying to do any signal-oriented electronics without an oscilloscope is like trying to drive blindfolded. OK, it is possible to develop audio systems with just a multimeter and an amplifier, but you are literally missing a sense. I did have an old analogue, CRT scope years ago, but gave it away when I moved to Italy. I’ve only done a tiny bit of electronics dev since then (simple guitar effects) and have got away with ears, just.
But my latest project will involve a lot of unknown signals, there’s no way I can make progress without a scope.
Standard scopes nowadays are Digital Storage Oscilloscopes (DSOs). The storage side is sweet, it’s possible to save snapshots of traces and often capture the raw data contained in them. But with Digital comes a caveat. Analog scopes tend to give a fairly true representation of the signal, in the given context (bandwidth, levels etc). Anything spurious, such as over-level clipping is immediately visible. Digital scopes rely on analog to digital conversion (A/D), which introduces factors such as the sample rate, filtering and resolution. Out-of -range signals presented here can produce misleading displays.

Requirements

Most of what I want to look at is in the audio frequency range, which is well covered by pretty much any scope worth its salt. For example, my old analog one went up to a 1MHz timebase, comfortably encompassing the nominal 20Hz-20kHz of audio. But because I’m going to be looking at circuits that may pick up radio frequency signals, a higher bandwidth could be useful. Being able to go down to DC will be useful too, for lower frequency signals and detecting unwanted offsets etc.
The signal levels I’m interested in are relatively low voltage, so there are no special requirements here (at circuit input some signals will be very low amplitude, but as the target systems will need to amplify these anyway, this shouldn’t be an issue).
For convenience, I want at least two simultaneous traces to be available – most circuits I’m likely to be looking at will feature an input and output.
Additional it will be pretty essential to examine signals in the frequency domain.
Finally, the scope has to be affordable.

Options

Benchtop DSO

This is the most obvious solution. These are available starting at around $500 – not a trivial amount, but definitely worth considering for such a vital piece of kit.

Computer Soundcard

Right at the low budget end is the use of a computer sound card and appropriate software. Remembering now, I realise I fibbed about developing guitar effects without a scope, I did actually use a soundcard and various (free) VST plugins to look at the signals.
But this approach is quite limited, and, well, clunky. It isn’t really viable to make accurate measurements, there’s no range changing switches built in, bandwidth and resolution can be overly limited (e.g. few sound cards go down to DC).

BitScope

This is an A/D converter which attaches to a USB port and has dedicated DSO software. The BS10 has excellent specs on paper, though they are dependent on host computer performance. The software will run on MS Windows or Linux and notably a Raspberry Pi. An Android version appears to be in the pipeline. Physically the BS10 is a small box which comes with a bunch of clip leads. It has two analog inputs, an analog output and and 8 logic inputs. A variety of applications were downloadable from the site, the key one being BitScope DSO. Once I’d realised this had to be run with sudo (to give access to /dev/ttyUSB0) it worked a treat.
The controls in the application aren’t entirely intuitive, after a couple of days getting used to them I’m still unsure e.g. how to adjust offset. For equipment like this, I’m afraid an on-screen user interface will never be as convenient as hardware knobs you can twiddle.
The DSO application also offers a frequency domain display (for one or both channels) as well as a basic signal generator. The freq display is very nice to have, though control of parameters is rather limited. For example, an arbitrary zoom would have been good, as would a variety of smoothing/averaging options.
Similarly the built-in signal generator is nice to have, but even more limited. It offers a range of fixed frequencies, producing a sine or square wave. This is OK for quick checks, but that’s about it.

Fortunately there’s a fairly trivial way of providing a versatile sig gen in the same setup at virtually zero cost. Whatever the host machine for the BitScope, chances are it has a soundcard. Hook a couple of jumpers leads to a jack plug, pop it in the headphone out socket, fire up Audacity and bingo!

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So as a substitute for a benchtop DSO, the BS10 is adequate but not outstanding. Call it 7/10. Given the price compared to dedicated hardware this seems reasonable.
However, chances are anyone working with analog signals in this day and age are likely to have digital aspects to their circuits. I haven’t tried this yet but from the docs the 8 channel logic monitor capability of the BS10 looks like it should be very useful in future.
For my current project, while I need the DSO facilities for circuit development, the BS10 should offer a very good foothold into another part. Again though I haven’t yet tried this, it also appears to be a very versatile data acquision system for recording signals. This can be done from within the DSO app or programmatically (with hooks from Python, I believe). The latter part I’m rather looking forward to, a hackable signal capture unit is very nice to have. I don’t yet know how sophisticated I need this side of my project to be, but the BS10 certainly is an option. Alternately I may develop with this interface, then flip to the cheaper BitScope Micro for production.
All in all then, the BitScope BS10 scratches a lot of itches.

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Author: Danny Ayers

Web research and development, music geek, woodcarver. Originally from rural northern England, now based in rural northern Italy.

2 thoughts on “Seeing the Signals (& BitScope BS10, first impressions)”

  1. “Once I’d realised this had to be run with sudo (to give access to /dev/ttyUSB0)…”

    Perhaps adding your normal logon user to group “dialout” might be sufficient. I do that to access USB-to-serial adapters on Ubuntu.

    Like

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