Has anybody used a USB sound capture device for an audio frequency
oscilloscope on a Raspberry Pi? xoscope is available using apt,
but I can't find any reference to what sound devices, if any, it
can use over USB.
If there are other USB oscilloscope options worth looking at
please post. I don't specifically need RF performance, but if
it's available it's worth a look.
Thanks for reading,
It is worth understanding what frequency range you're interested in.
Soundcards are typically 20Hz-20kHz.
SDR often has a limited bandwidth and doesn't go below ~30MHz.
Often for oscilloscope purposes you're interested in DC, which is outside
the range of this hardware. Soundcards may go that low, or maybe it can if
you remove a series capacitor.
all you really need is a decent A:D with a good bandwidth.
Then RPi could use SPI or I2C to talk to it. Then you can make a
charting application to display the trace, or use an existing one [I
assume such things have been done before, it's not a new idea]
Sound card o-scope would limit to audio bandwidth. An A:D that can run
at frequencies from DC to above 1Mhz is probably what you want. Maybe
an ADC that is capable of doing video would work... [you'll have to
search but I remember seeing them]
(aka 'Bombastic Bob' in case you wondered)
'Feeling with my fingers, and thinking with my brain' - me
not built mine yet (too much trigger happy shopping, it's sat on a shelf).
Kuman JYE DSO Shell Oscilloscope DIY Kit with Open Source 2.4 inch color
TFT LCD+ Shell + DIY Parts + Probe 15001K (SMD pre-soldered)
Ah, sorry I understood the opposite - I missed or misunderstood "I don't
specifically need RF performance" as if OP was asking for RF explicitely :)
I know only the PicoScope from the Automotive angle, but could be there are
cheaper products that work with linux.
I suspect you'll get better suggestions if you can outline what you are
trying to do.
For instance, are you trying to get analogue output from digital
recordings or do you want to digitise audio from a mic or turntable?
What pert of the system (analogue or digital) do you need to trouble-
A 'scope may be best for audio signals, but something as simple as a
logic probe may be good enough to sort out problems on the digital side.
Hantek is the name, or at least one of the names, many people rebadge
them. There is openhantek6022 which works for the cheapest scope.
It's OK for DC and audio, which is all I need these days. If I have
frequencies a bit higher to deal with, I haul out my ancient Tek 465B,
which weighs about fifty times as much as the Hantek device.
Xoscope's webpage says it supports ALSA as an input source, so as
long as a USB audio adapter is working with ALSA (the cheap Chinese
ones seem to do so without issues) it should be fine.
It will have a series capacitor to block DC. You'll need to either
remove this (might be difficult if it's a small indistinct-looking
SMD part) or use a chopper circuit like this if you want to measure
For more sensible input impedence (so the behaviour of the circuit
doesn't change when you probe it), the buffer circuit shown at the
xoscope homepage would also be recommended:
Of course at this point you've got a significant amount of
front-end circuitry for your "simple" sound card oscilloscope. For
a data logging application that might be quite reasonable, but for
basic troubleshooting maybe it would be easier to just buy an old
CRO (Cathode Ray Oscilloscope), which has the added benefit of
working outside the audio frequency range.
There are some decent dual channel, 20MHz oscilloscopes appearing on eBay
and at pretty reasonable prices too. Find one locally if possible to same
freight costs: a good older 'scope is both heavy and bulky.
Also, its worth noting that a 'scope can also be used as a logic probe: a
straight high line is a stable '1', a straight low line is a stable '0'
and either a pair of lines or a square wave, depending on scope scan
speed vs signal frequency, indicates a digital signal.
Mine is a dual beam 20MHz Hameg I've had since the mid '80s and used for
everything from trouble-shooting a floppy drive interface I built for a
6809 system to checking the state of 50mAH NiCd batteries (they were used
in a timer to pulse a solenoid with a 500mA, 15mS pulse: the shape, depth
and width of the of the battery's voltage drop when the solenoid was
operated was an excellent indication of battery condition. As it aged the
voltage drop changed progressively from a 15mS wide drop with a flat
bottom and instant recovery to a deeper, wider shape with no flat bottom
and a longer recovery slope. When the flat bottom was gone it was time to
replace the NiCds.
My hope was to elicit reports of practical experience....
The motivating problem is monitoring power supply voltage on a Raspberry
Pi4 during boot and disk spin-up. I'd like to see the voltage rise, sag
during boot and spin-up and then stabilize. Depth and duration of the
sag would be the most essential observation.
Basically power supply circuits. A "stop trigger" that halts recording
when something interesting happens is much desired.
Thanks for writing!
Hantek seems to be Windows-oriented, I have great respect for Tektronix,
but analog scopes are no help with transients absent a Polaroid camera
and a stable trigger pulse.
Thanks for writing,
Ok, that's a good hint. I'm looking at something like:
There are reviews saying it works with Raspberry Pi, so maybe it'll work
with xoscope. It doesn't have to be good, just good enough to catch
sags and spikes on a timescale of milliseconds.
Thank you for the link!
I'm experienced with analog 'scopes and don't want one. They aren't
useful for catching one-off transient events, which is what I'm looking
for. Something with a stop trigger is essential. A freestanding DSO
would be nice, but I won't use it enough to justify the cost and storage.
Thanks for writing,
A search for raspberry pi DSO revealed a range of devices called
bitscope which (if as good as advertised) look like handy devices, probably
overkill for what you want but it would have cleared several feet of bench
space in my 1980s labs.
Steve O'Hara-Smith | Directable Mirror Arrays
C:\>WIN | A better way to focus the sun
may be worth a look - its (very) small, fully open source software and
while I had a different use case, worked for me. Looking at the web
site, I probably ought to update my software version before I use it