I have one of the more basic UNI-T multimeters and can highly recommend it. It's always there when I need it (the single 9V battery keeps it going for years) and has great precision.
One thing that I don't have - and really want to have - is a variable power supply with constant voltage/current. They can be used when you have an unusual battery you need to charge safely, for instance. Unfortunately, they always seem inordinately expensive considering that all they are inside is a few coils and some ICs. I've looked into building one myself, and found the very informative EEVBlog series on it[1]. However, there's one thing I don't understand: how do you compensate for the voltage drop over your current measuring resistor? Is it a simple linear equation and you just boost the voltage accordingly? I'd love an explanation!
Yep I've had that Korad for years and it's great. I'm sure there are far better power supplies out there but this one is great for hacking on digital stuff and maker projects that aren't demanding or sensitive to the PSU quality (which is like 90% of projects).
In a power supply you can sense your output voltage with a differential amplifier between the positive and negative outputs that way the voltage drop across your current sense resistor is not included in the measured differential voltage. Alternatively you can use high-side current sensing where your current sense resistor is before your positive output. You can also use a differential amplifier for that, but there are purpose made current sense amplifiers which are probably best.
The reason lab PSUs are so expensive is that they are incredibly stable. A regular cheap power supply will provide a sort-of stable voltage, but there will be a loooot of noise on it. Meanwhile, even a basic lab PSU will guarantee the output voltage to within a few mV, no matter what you throw at it. This allows you to completely rule out the PSU as a potential source of faults.
One thing that I don't have - and really want to have - is a variable power supply with constant voltage/current. They can be used when you have an unusual battery you need to charge safely, for instance. Unfortunately, they always seem inordinately expensive considering that all they are inside is a few coils and some ICs. I've looked into building one myself, and found the very informative EEVBlog series on it[1]. However, there's one thing I don't understand: how do you compensate for the voltage drop over your current measuring resistor? Is it a simple linear equation and you just boost the voltage accordingly? I'd love an explanation!
[1]: https://www.youtube.com/watch?v=CIGjActDeoM