Too bad to hear that man! Pay attention to Dave's giveaways, he sometimes does one pick based on a story and you can probably qualify for it! Same thing can happen in other places, you could get a nice gift someday. Keep your projects well organized to show people, like the meter repair, or this project, they can help you at some point, it's important for people to see what you've done. This forum can be a good place, just don't loose track of your posts.
Here's your old post, so you can upload your results there. For the diodes, there's probably enough space there to fit a few diodes to protect the inputs, but you could also use external resistors to measure current.
You could get 1% resistors or even better, a broken meter could give you what you could need. If you prefer to work a bit more, you can use ten 10Ω resistors, measure them in series and note the value, then connect them in parallel and you will get an 1Ω resistor with 1/100th the value you measured in series with better tolerance than the components have. And you will be getting your toes wet in metrology, the 100Ω is easier to measure. For the 0.01Ω get's trickier but having the known 1Ω resistor you are half way to it.
https://www.eevblog.com/forum/repair/fluke-87iii-broken-current-input/ Coming back to the Arduino to look at signals, if you don't want to get to your computer you will need some sort of display, other option, you might be able to find a cheap wifi module, those ESP8622 are everywhere now. From there you could pick the signal from the computer without any risk for the computer, and if you run from batteries or even a power bank you will have a floating scope which is great! Be careful with it. Also, you will have much more memory, like a few MB and the sampling freq is likely to be higher.
If you go back to the computer idea, or the arduino to the computer, there are ways to protect the channels pretty well, a fuse, a few resistors and diodes can get you a very long way there. A well protected circuit for the computer isn't unreasonable, the thing is you need to protect not only the signal input but the common, using a low current fuse, a 1k resistor or something and a pair of diodes to ground would do a pretty decent job. For the signal you want a high value resistor, at least 1M, if you can get a ~5V zener diode great, or a few in series. That after the resistor will limit any signal going to the next stage, the resistor would only let pass 100µA at 100V, so hard to damage anything. After that, an attenuator, which could be a 100k or greater potentiometer.
I have to tell you, when I started, 15 years ago or something, I wouldn't even dream in getting an scope, arduinos weren't available and I was far from using pic or getting a programmer for it, I think it could be done with parallel ports back then though. Long story short, I only got my scope a few month ago, now I work and can justify expending real money on it, so far I was getting away without seeing the signals, which can teach you a lot on how to know what's going on without looking at it. It's much harder but you can do a lot of things without one, don't hurry into it, as I mostly did audio, a small amplifier did the trick, also should be protected but damaging the power stage of a scavenged radio isn't a big deal, and hearing can tell you a lot from the signal, like if there is just noise or has some oscillation, if there is signal still present in the path or you loose it in the previous stage, etc. If you can build something would be great and really useful, but don't think that till you don't have it you can't do anything with electronics.
JS
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