Cheap oscilloscopes and PSUs?

[skillz21]

I want to get an oscilloscope and a PSU, (PSU gets preference) I only need the absolute basics when it comes o the scope, and it needs to be as cheap as possible. With the PSU, just a general 0 - 40 or so voltage one with a few amps output is fine, once again needs to be cheap. I'm an absolute beginner, so I don't have a very large budget. Could someone recommend something for me?

[tautech]

Building your own simple PSU is a hobbyist right of passage.

Don't set your sights too high just something simple using an LM317. Get the datasheet, it has simple circuits to work from.
For the power source you can use a 1-2A wallwart, most of us have a selection just lying around in boxes.
Laptop bricks can be good too as they're generally a bit higher voltage.
If you have a 12-24V transformer lying around that's one of the more expensive parts and the rest of the bits and bods don't cost much.

If the supply is AC then of course you'll need to rectify it, all of which is a valuable learning experience.

[Peabody]

Dave has a couple episodes, one fairly recently, on getting a used $50 analog scope on Ebay or Craigslist.  If that's within your budget, and you can find one, that would probably be your best option for a low cost scope.

[skillz21]

With the LM317, how do I do current limiting? Or is it possible to get a different IC that does this?

[tautech]

With the LM317, how do I do current limiting?

If you mean adjustable then it's not dead simple.
Otherwise just rely on the inbuilt current limiting and thermal overload protection. Specs for each are in the datasheet.

[Twoflower]

How about the LM723? There many circuits floating around with about 0...30V and 0...2A. They're available as kits for little money in various variants.

[skillz21]

With the LM317, how do I do current limiting?

If you mean adjustable then it's not dead simple.
Otherwise just rely on the inbuilt current limiting and thermal overload protection. Specs for each are in the datasheet.

I want it to be like a proper power supply - adjustable, and for things like power LEDs you need to have a current limit, limit, or they go pooof (or so I've been told). But is there another IC I could use to fulfill my needs?

[Twoflower]

As said there are circuits with the LM723 that can adjust the current and it worked for me many years and it is still alive and kicking. Still I personally never used this PSU in CC operation. Only as kind of over current limiter to limit any damage if something went wrong.

Yes LEDs have a very steep U-I curve over a certain voltage and start to draw higher than allowed currents. But that steep part of the curve actually the operating point of LEDs. For individual LEDs you should still use a series resistor. Mainly try to set a 20mA current limit for a 5mm LED on a poti that goes from 0 to 2A. Unless you have two potis one coarse and one fine or a 10-gang poti you will never set a nice operating point. Not even talking about doing that reliable. Plus most likely the set current will drift in cheap circuits. Especially in such small areas. If you have a hard requiremend on this you might need to spend more money to do this.

But if you talking about LED stripes. They usually can be operated with the rated voltage (5, 12 or 24V are common) without the need of a current limiter.

[sevenTech]

For these DIY solutions, I have great experience with LT1074 switching regulator. It is the one of the few that has current limit capability (just by soldering potentiometer to Ilim pin). Works pretty well.
Only drawback is that it is little expensive...around 15 dolars. So it is better to double check the circuit so you will not burn it :-)  But note that this current capability is only present on 7pin TO-220 variants. Like LT1074CT7 and LT1074IT7...Output capability is 5A (with passive cooling)

[daybyter]

10$ DIY scope:

http://www.stm32duino.com/viewtopic.php?t=107

or look for the hantek 6022be or bl USB scope. There is a long thread here in this forum.

[cdev]

That super cheap SM32F103 oscilloscope is a hell of a cool beginners project.

[tautech]

With the LM317, how do I do current limiting?

If you mean adjustable then it's not dead simple.
Otherwise just rely on the inbuilt current limiting and thermal overload protection. Specs for each are in the datasheet.

I want it to be like a proper power supply - adjustable, and for things like power LEDs you need to have a current limit, limit, or they go pooof (or so I've been told).

We all want our first PSU to be the ducks nuts, I did too and after some time looking at adjustable current and foldback limiting I decided to build simple and just let the regulator IC do it's job and preserve itself. That's why LM317 is so popular....usage is simple, especially for the beginner. I chose a TO-3 package LM338 for those reasons and higher currents. Scared of frying components, we all are so without adjustable current you need engage brain and ensure you haven't made mistakes. You won't get everything right but that's how we learn....right ?

You can build something much better with other IC's but then you exit the simple stage and at the risk that if it's a flop when you could've spent the money on something all ready to go. I still say that your first PSU should be homebuilt and simple and depending on what you have lying around also very cheap.

When I needed better I looked at cheap switching supplies, yeah they're a little noisey but fine for many uses.
This is one I would recommend:
https://www.eevblog.com/forum/testgear/cheap-variable-switching-power-supply/

[rstofer]

I was working on a vintage Z80 project and when I brought it up for the first time, I made sure to limit the current to 100 mA.  Good thing!  There were a couple of bus contention issues related to the documentation (jumper settings).

I bought the Rigol DP832 a while back after having used wall warts and batteries for decades.  The current limiting feature is very important.

If you can't get adjustable current limiting, don't bother building the PS.  The best case alternative has the regulator going up in smoke, the worst case is you lose the regulator AND the project.

Dave just did a couple of videos on PS modules.  I didn't pay particular attention but it seems they have both adjustable voltage and max current.  And they're inexpensive!

https://www.eevblog.com/2017/10/11/eevblog-1030-20-diy-bench-power-supply/
https://www.eevblog.com/2017/10/12/eevblog-1031-25-dps3003-psu-module-characterisation/
https://youtu.be/Q2rvAoO-MIA

[ivan747]

With the LM317, how do I do current limiting? Or is it possible to get a different IC that does this?

If you have an AC transformer that outputs ~24V:

https://m.banggood.com/0-30V-2mA-3A-Adjustable-DC-Regulated-Power-Supply-DIY-Kit-p-958308.html

You should also get the fan. Is loud as hell but the design ends up very compact. You could also use an old PC heat sink + fan.

If you are interested I can show you my version of the kit.

[kjr18]

Few months ago I made small portable power supply, in small plastic case I managed to pack a 2 pack of 18650 li-ion batteries, tp4056 + DW01 charging module, cheap chinese boost module, and a very common on ebay module. On the side of the case are two rocker switches, one for power, second one for current limit selecting, and two cheap banana plug sockets. It's amazing that it worked when I made it (most of the times when I make something, they don't really work as intended, or at all). These cheap modules are a some way to make a simple power supply, as they show voltage and current, they not as accurate as other more expensive solutions but they quite handy at times. Some small modifications, and you're good to go (just replace pots for some easier to use ones).