Arduino oscilloscope - DIY entry device

RE: Arduino oscilloscope - DIY entry device

neris.io — Fri, 06 Oct 2017 17:06:32 GMT

Very cool!

Wanted to share 8x Arduino Logic Analyser and protocol decoding via sigrok https://hackaday.io/project/26356-ginlogic-arduino-due-uno-ginlab that could easily be accomplished via reading a port and dumping raw data

Also Arduino(and other hardware) HTML oscilloscope coming sometime in the future https://hackaday.io/project/19374-ginscope-science-toolbox-oscilloscope

Will check this project later, when I get my lab back!

RE: Arduino oscilloscope - DIY entry device

jc2048 — Fri, 01 Sep 2017 08:34:45 GMT

With your follower circuit simulation, try it with a sinewave going in.

Then you can think about whether the circuit configuration you've chosen can meet your requirements and maybe consider other possible circuits.

(As a general note, you can't depend on the model being accurate once you move away from the normal operating conditions like operating within the supplies.)

RE: Arduino oscilloscope - DIY entry device

idanre1 — Sat, 26 Aug 2017 13:52:10 GMT

Questions about op-amps

I have tried to find an op-amp for my purposes just as an exercise

I encountered http://www.ti.com/lit/ds/symlink/lm6142.pdf

TI claims you can provide Vin lower than the negative power supply.

How it can be done?

Also I coudn't find a graph saying how much time I can provide lower than supply signal without tempering the output

I searched for Vout depends of Vin&supply, what am I missing?

Also according to the datasheet this opamp is good for ADC application

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MCP6024 also have CMRR of 85-90 db.

Is there a reason why TI says their opamp is good for ADC but microchip not?

I couldn't find which technology types both the opamps rely on.

Is it CMOS? JFET? BJT?

Where it can be found?

Regards

Idan

RE: Arduino oscilloscope - DIY entry device

jc2048 — Thu, 24 Aug 2017 12:53:32 GMT

Are you intending this to run from the +5V Arduino supply? If so, the op-amps need to run on 5V [a lot of older ones didn't]. The outputs need to get to the rails [old bipolar op-amps mostly didn't], otherwise you'll restrict the range of the ADC input that you can use. You'll also probably want the inputs to work to the rails too (I said probably because we don't know the circuit yet) [again a lot of older bipolar op-amps were poor at this - doesn't mean they were bad op-amps, just inappropriate for what you want here]. If the scope is going to be fairly precise, you don't want the input bias currents and the current and voltage offsets to be too large, though that isn't too much of an issue here [traditionally, FET and CMOS op-amps were good for low bias currents but often poor for offsets - but that has changed a lot in the last decade or two - better automation means they can be trimmed at manufacture]. You also need enough bandwidth from the op-amp so that it can work properly over the range of frequencies you will be looking at with the scope. The quick measure of bandwidth is the GBWP (gain-bandwidth product) - that's the frequency where the gain of the op-amp falls to unity; it needs to be much higher than the highest frequency you are working with (how much higher will depend on the circuit configurations you use, but a GBWP of 5-10MHz is the right sort of area for 100kHz of bandwidth at the scope input as long as you're not asking for too much gain from the amplifier).

Presumably, you don't want to be paying $20 for it either.

That will reduce the number of possible contenders quite considerably. If you also throw in the requirement that it be a conventional package rather than surface mount (to make your prototypng easier) then you're probably down to just a few devices from each manufacturer (they'll all have something that will do this because they're agressively competing with each other for your chip business.)

Here's one possible contender. If you download the datasheet and look through it you'll see how it's specced and you should be able to locate most of what I've just gone through amongst the tables.

MCP6024 - Amplifiers and Linear - Linear Op Amps

Other manufacturers you could look at include TI (Texas Instrumenats), AD (Analog Devices), ON Semiconductor (don't know what the ON stands for!), and LT (Linear Technology).

What do you want to do next?

Either you could try doing something for yourself or we could give you a circuit to experiment with. If you've already done some op-amp circuits, you might want to try piecing something together for yourself as a learning exercise (and for the challenge), if not you might prefer to have an example circuit with an explanation to get you started and give you something to play with.

RE: Arduino oscilloscope - DIY entry device

DAB — Tue, 22 Aug 2017 19:02:52 GMT

Very nice post.

Making your own test gear is always a useful project.

It helps you learn more about hardware and software.

The resulting project provides you with a useful addition to your testing capabilities and your overall knowledge.

Well done.

DAB