I have a computer, I need a simple oscilloscope

I need to see a plot of the voltage produced as a magnet passes a pick-up, at varying rpm. Can you recommend a program to use on a lap-top or tablet (Windows 10) - to produce a plot either in degrees round a circle or on an x-y graph? It is only for one series of measurements, so cheap if possible.

Regards, Tim

About 5 years ago I played with Soundcard Oscilloscope which probably does what you want and is free.

Disadvantages from memory: works off audio input to the soundcard so can't measure voltage, and though it does a good job with time the max frequency will be about 48kHz. Oh, and be careful not to accidentally squirt high voltage into the computer! Should be OK for rpm measuring.

Dave

Put 'usb oscilloscope' into an eBay search. Cheapest, UK sourced single channel is £23. No enclosure or probe. It is not clear what data logging ability it has.

Next is a dual channel from China for £25, with enclosure, no probe, software to send your life savings back to the homeland* and what appears to be proper data logging.

Hantek do one for about £70 via amazon and CPC have a Vellerman one for £54.

* easily defeated by putting a tinfoil hat over the device.

Don't worry about the tinfoil hat, 95% of computer motherboards are made in China.

Duncan

A cheap option if you just want to analyse digital 0 to 5 volt signals is a diy usb scope using an Arduino. This is a link to a site showing how to use an Arduino uno. **LINK** . I have made one using an Arduino nano which is a bit cheaper than a uno. The last one I bought was only about £5 from hobbycomponents.com inc p&p

The instructions for programming the Arduino and the software to run on your pc are here **LINK**

This is a screenshot of the sort of display you get

Stuart

That's not a straightforward measurement, and not something an ordinary oscilloscope can easily do. Way back in the mists of time one could use an oscilloscope to produce Lissajous figures using two (sinsoidal) signals to produce a pattern from which frequency, phase and amplitude of a signal relative to a known signal could be deduced. But the scope needs two inputs, the normal Y input, and one for X which replaces the internal time base. I haven't seen an X input on a scope for decades.

I assume that a voltage proportional to polar position is not available? However the voltage signal from the sensor should be periodic and any reasonable scope ought to have cursors, or automated measurements, that can be used to determine period and hence rpm.

I'd forget about an X-Y display and look for a simple single channel USB scope board. I can't help with specifics as I'm only familiar with the offerings from Pico Technology, and they are probably outside of the budget. They are good, but can have some issues, although they wouldn't be a problem in the proposed project.

Andrew

Hi Tim,

If it's a one off I could lend you a Pico Technology Picoscope 2203 dual channel "proper" USB 'scope adaptor.

see https://www.picotech.com/oscilloscope/2000/picoscope-2000-overview

It is capable of doing what you want.

PM me.

Robert G8RPI.

Edited By Robert Atkinson 2 on 23/09/2022 20:51:10

It may be that I used the wrong term when I said 'an x-y graph'. A level physics was a very long time ago. I do not need lissajous figures, I just want a plot of voltage (y) against time (x). The critical thing is to measure the bulge in output voltage as the magnet passes the coil, and to look at how that lump varies in size as the speed varies. And then to look at the effects of rsistance, diodes, capacitance, induction, distance etc, added to the circuit at a fixed rpm.

And so far, it does look as if the Soundcard prog should meet the need, but it is rather quiet about what exactly should be used as a connector to the system tested. I am ploughing through the manual, though, so hope is not lost.

And sorry, the idea of getting to grips with yet another impervious technology at the wrong end of life is what I am trying to avoid. So, not and Arduino, thanks, however clever they might be.

Regards, Tim

The soundcard oscilloscope manual is purely for the software. As the connector is a piece of hardware, you need to look at the manual for your soundcard (hardware) to determine how it accepts input from the world.

About the only relevant bit of the soundcard 'scope advice is on the webpage itself in the section 'Signal sources'.

It is well worth glancing at this site in addition: https://www.nutsvolts.com/magazine/article/turn-your-computers-sound-card-into-a-scope

Pay particular attention to the following, quoted verbatim:

"Whenever you connect an external signal to your sound card, you run the risk of possibly applying too large a transient voltage and blowing out the front end of the sound card. While all sound card inputs are AC coupled and generally ESD (electrostatic discharge) protected, there is always a risk of damaging it. You do not want to destroy your PC’s built-in sound card!

To reduce this risk, I strongly recommend when you want to connect an external signal from one of your projects, do not use your internal sound card. Instead, purchase a low cost external USB sound card."

As you intend to "look at the effects of resistance, diodes, capacitance, induction, distance etc, added to the circuit at a fixed rpm," do you think there is a chance, however small, of exceeding the allowable input parameters of your soundcard and destroying it?

Hello, Tim,

This might help you - at least some options.

Regards

Audio Card Oscilloscope

Edited By An Other on 24/09/2022 16:51:04

Probably not a good idea for the input to be AC coupled. I'd go for an external box specifically designed as an oscilloscope. Or take Robert up on his offer.

Andrew

Obviously a proper USB oscilloscope is best but I think the sound-card protected by a pot would be OK. Something like this (assuming the pick-up is a coil):

The wiper is connected whatever audio input connector is available on the computer - usually a minimum of two 3.5mm stereo jack sockets for microphone input and line-out, but a third for Line-input is common too.

Operation: set the wiper to ground and set the wheel and magnet spinning. Use the oscilloscope software or window audio mixer to select the input and set the amplification to about 90%. Then gradually turn up the pot from zero until the signal appears.

The maximum input voltages I've noted on the diagram are maximum without distortion. I'd expect a sound-card to have a considerable safety factor, probably at least a volt or two, but don't push your luck!

Most sound-cards are AC input, but I don't think it matters for what Tim is doing. A coil will generate a wave as the magnet approaches and recedes which will be seen by the sound-card and displayed.

The chief risk of borrowing Robert's Pico is the temptation to keep it!

Dave

And that is the flaw in the plan. It relies on the knob-twiddler performing his duty with 100% reliability every single time without fail after every change to the input conditions.

If you could show something with a kind of dead-man's control on it that absolutely cannot put anything into the sound card input without positive human action, that would be the beginning of a way forward.

If you can incorporate something in it that will prevent overvoltage altogether (perhaps caused by an involuntary jerk due to sneezing when adjusting the pot), that would increase the reliability of the system.

Hello Tim,

i build this one with an Arduino Nano https://sourceforge.net/projects/scopino/

The scope is more basic ,but i tested it with my model receiver with servo signals and it worked OK.

There is an other application called serialscope https://x-io.co.uk/serial-oscilloscope/

I build both and they are different and both useful. The hardware is based on an Arduino Nano input divider potentiometer al cheap parts.

Werner

You'll probably get a working scope off FB marketplace for under £20. It will do all you want and more.

I looked up the spec for my Tektronix digital scope; the AC cutoff frequency is about 10Hz, equivalent to 600rpm. I suspect that AC coupling may well give a false picture of the waveform.

Andrew

I'm not sure, now, whether a computer-based solution will work well for me. The intention is to calibrate a pick-up design for an internal combustion engine. Normally such devices are driven at half engine speed to fit with the four-stroke cycle. The engines I am looking at have a peak rpm of 4,000rpm, and so the pick-up goes at 200 rpm, which is 2,000 / 60 Hertz = 33 and a bit. Feasible. But at tick-over - at a camshaft around 20 rpm or on a good day, lower, this means a signal at 3 and a bit Hertz. And I'm fairly sure that a sound card (the input mechanism used in a computer-based system) will be out of its depth. ( I love mixing metaphores).

So, perhaps the idea from Robert (resp[onse no 6) is worth a second look. Have I got this right, chaps?

Cheers, Tim

Hi, I’ve used a Picoscope to show pulses from a rotating disc and a crank sensor (hall effect) , works well.

Red pulses are from trigger and wheel.

There are 35 pulses and 1 gap per rev.

Blue pulses are from HT coil.

Cheapest Picoscope is £114 at CPC

Hope this helps

Maurice

A proper digital 'scope is what you need.

Picotech do specialised software for automotive use. I's very nice but needs one of their "automotive" scopes.
i do have a couple of those. It automates lots of measurements and tests with clever trick like compression testing with just a probe clipped on the battery cable. They also use a pressure sensor with a tube stuck up the exhaust so you can compare valve V ignition timing and the relative output of each cylinder. I have on of their kits but they start at about £1000 new.

https://www.picoauto.com/

Tim,
do you have an older PC or laptop with a parallel printer port (25 pin connector) ? if so the lent picoscope could be an older, non-USB one that works with the automotive software. (it does not support the advanced diagnostics)

Robert G8RPI.

Hi if I recall correctly the sound card scopes are limited to 1v peak to peak. You could use a times 10 probe setting to reduce 10v to 1v peak to peak. I have used a similar setup with a usb soundcard (a couple of pounds on ebay) to build a gamma spectrometer which worked well recording low count rates worked well.

However, a usb scope (cheap) would be more flexible especially if you are experimenting with circuits etc and maybe a trigger input to help to capture transient signals. Pico scopes are very good, I have one of their top 4 channel models with logic analyser and waveform generator models, and taking up Roberts offer might be the easyest way forward. But sometimes a stand alone scope is better, I picked up one for £10 at the local army store.

Barry