Spec of bench supply and oscilloscope for electronics beginner

I can program but only have a very basic knowledge of things electrical and electronic - enough to keep me safe. For a while I have been thinking that perhaps I should try to increase my understanding of electronics. I will never be a serious electronics designer but I would like to play a bit more with small servos and steppers and breadboard using simple Integrated Circuit chips.

I will be working with Arduino and Pi boards.

To me it seems sensible to start by getting a bench power supply and then an oscilloscope. What specifications should I get though bearing in mind that cost is an important consideration?

I would be interested in what features you think the equipment should or should not have and why.

A tool that I have that I find useful is a Saleae Logic clone logic analyzer that I got from Ebay for less than $10.00. Together with the free Pulseview software it does most of what you would use a scope for while doing Arduino projects. A handy feature of Pulseview is the protocol decoders.

ardly: To me it seems sensible to start by getting a bench power supply and then an oscilloscope. What specifications should I get though bearing in mind that cost is an important consideration?

While I do have a couple of bench power supplies and they have their uses, the fact is that for "small servos and steppers and breadboard using simple Integrated Circuit chips", you want fixed (switchmode) supplies of certain current ratings. It is generally inappropriate to operate Arduinos from other than 5 V, so the most useful is a 5 V "phone charger" with a USB output jack (which is exactly what is recommended for a Pi).

A 2.1 A unit will power most things (later model Pi·s require more), and you want a few of them so you can have various things set up at once. They are relatively cheap (though you should get ones of a proper brand) and often available from "thrift shops", "garage sales" or specials. Those from eBay sellers in China are somewhat more dubious.

Servos require at least 1 A each, so a fixed 6 V supply of 5 A or so rating would be most useful (and not so many "bench supplies" have this rating).

There are also many 12 V switchmode "plug pack" or "wall wart" supplies of 1 or 2 Amps floating around, look for discarded ADSL modems or similar network equipment as well as 9 V units.

As for DSOs, these are cheap and quite useful: |500x500 It comes in various kit forms requiring different degrees of assembly, but that is a good exercise in itself. :astonished:

There's kind of a gap in power supplies. You can get cheap and low-power (obviously) and adjustable supplies are really useful and relatively cheap. But the jump in cost between an adjustable supply with 1A and one with just 2A is huge.

There are three advantages to a "bench" power supply over the plentiful 5V supplies:

  1. The voltage is adjustable - you can work on 12V and 5V projects easily. You can check that your "12V" project will survive 14V when the battery is on the charger. You can check that your project works at the low-battery voltage cutoff.

  2. There is a current limit - you can plug your project in for the first time with a 20mA limit and nothing will heat up so fast that you can't turn it off and fix your mistake.

  3. There's voltage and current meters - you can see how much current your project is pulling and quickly turn it off if you see it has hit the limit.

But powering a servo or motor at just-over-one-Amp with that sort of supply is problematic. They are almost always rated at 1A or less. Buying more current costs hundreds of dollars.

A 13.8V fixed supply with lots of amps can be had very cheaply. I have a 20A one that was relatively cheap. I have a 10A supply that has #1 and #3 but not #2. But most of the time I can work with my low-power adjustable supply that does all 3 functions.

Oscilloscopes are another problem entirely. They used to be really expensive. The good one in the lab at university cost more than my parents' house. Now you can get one better than that for just a few hundred. The really cheap ones like the photo above are much too limited. They often can't go over 5V input, which is really un-useable for 12V projects. USB based scopes can be good but my computer has the Arduino IDE on it and I don't have enough screens to put the scope and Serial Monitor side-by-side. I really love a dedicated machine sitting on the bench with proper buttons and knobs.

Fortunately you don't need high performance for a scope on an Arduino. Even the crappiest one will be able to resolve your Arduino signals. A logic analyzer or "mixed" scope is useful - some even decode I2C for you - but not essential. I suggest you buy the absolute cheapest one you can find which looks like a conventional bench scope and has two inputs. The handheld ones seem like a good idea and they're cheaper but I can assure you that they are a waste of money unless there is some special requirement you have for a handheld.

I am a bit surprised by the comments on power supplies. When I have been looking around there seemed to be quite a few 0-30V 5A supplies but then there was a big price jump when you went above 5A. Here is a site that is typical of what I found; https://makeradvisor.com/best-bench-power-supply/

I was thinking was that I could power an Arduino or Pi using USB and then use the bench supply to power the rest of the equipment for example a couple of 1A servos - am I wrong in that? Zapping things worries me and the Eventek KPS305D seems to have lots of protection. Are there other things I should be thinking about?

On the Oscilloscope front I like the logic analyser idea but maybe to start something simple like @MorganS suggests, dedicated and with real buttons is the way to go - but what spec?

There is a price jump between 2 and 4 channels so a two channel scope seems best. Most scopes seem to be digital now so I guess that is the way to go? The Arduino has a clock speed of 16MHz so does that help decide the bandwidth of the scope if so what should it be? Are there any other features I should look for?

Let's start with this... What's your financial situation? How would feel about spending $1000 USD?


The one thing you REALLY need is a multimeter and I assume you have one.

I think my meter cost between $50 and $100. (I'd say inexpensive but not cheap.) Someday I'll probably upgrade because it doesn't have a low-AC voltage range. (I suspect it has a diode or bridge rectifier for AC.) It has a continuity beeper, and that's a feature I'd highly recommend. (You can check connections, keeping your eyes on where you're putting the probes, without looking at the meter.) It's also auto-ranging which is also a handy feature.


I've been working in electronics for almost 40 years and playing-around with electronics for longer than that... I don't own an oscilloscope. At times I have "lusted" for one but I never really needed one badly enough to spend the money. But, I do have 'scopes at work and once or twice I've brought my hobby-projects to work to use it.

My Tektrinix 'scopes at work probably cost in the ballpark of $3000 - $5000. If I were buying one for home I'd be looking for something in the $500 range. I don't want some "cheap" portable thing, or some "cheap thing" that works with the computer. I'd want a real bench-top scope with all of the knobs, low-voltage ranges, 10X probes, and over-voltage protection, etc.


I built a little bench supply with fixed +5V, +12V, and -12V. (It's got regular linear regulators, so less than 1A.) I don't remember how much that cost me, but it was probably $50 - $100. (It seems like every project costs $100 when you add-up the cost of the cabinet, switches, connectors, etc.)

I got-by for many years without a power supply - Whenever I'd start a new project, I'd simply build the power supply first. I still build (or buy) the power supply first, but it's handy to have a little bench supply.

A work, I have a bench supply with 0-5V variable and dual 0 to +/- 20V outputs. It's got a built-in voltmeter and ammeter (the meters can be switched to any of the 3 outputs). It probably cost $500. A voltmeter is almost mandatory with a variable supply. The ammeter is super-handy because it's a pain to measure current with a multimeter. (I measure voltage and resistance every day, but I very-rarely measure current , except with the meter built-into my bench supply). The one feature it's missing is an adjustable current limit.

I use one of these.

http://www.mpja.com/Variable-Dual-0-30V-3A-and-Fixed-5V-3A-Benchtop-Supply/productinfo/29623+PS/

These go out of stock quickly, keep a eye on the link and get one as soon as they get them.

Let's start with this... What's your financial situation? How would feel about spending $1000 USD? .....

I've been working in electronics for almost 40 years and playing-around with electronics for longer than that... I don't own an oscilloscope. At times I have "lusted" for one but I never really needed one badly enough to spend the money. .... I'd want a real bench-top scope with all of the knobs, low-voltage ranges, 10X probes, and over-voltage protection, etc. ......

I got-by for many years without a power supply - Whenever I'd start a new project, I'd simply build the power supply first. I still build (or buy) the power supply first, but it's handy to have a little bench supply. ...

I would lust after the $1000 USD equipment but it is too much. My idea is to get advice on the specification first then look and see if I can justify buying it. There is no point in buying something that does not meet the spec. and if equipment that meets the spec is too expensive well that is life.

You have not needed a scope and I admit I was wondering if perhaps I would just be getting a costly toy, but I am sure I would learn a lot from it.

My plan was to get the bench power supply first as that way I could make projects that require a range of different voltages. You built your own power supplies but that means you obviously have a lot more knowledge than me. Buying a supply reduces safety concerns and also I am more interested in digital than analogue electronics. It seems that a 0-30V 5A supply can be had for around $60 USD which does not sound too bad.

If I do progress any small projects with a supply and a meter then the next step would be a scope.

For a scope I lean towards an on the bench dedicated model (not PC based) but something simple, not with a lot of features I might never use. $500 USD would be pushing things. Something around $300 USD would be good and I did see a Hantek DSO5102P at about that price, oddly the 100MHz version was cheaper than the 70MHz model.

Hello Ardly,

Have you considered making a bench power supply as part of learning about electronics? With the obvious caveat that you need to understand what you are doing around mains, building a bench PSU could be an interesting project.

I have a variable PSU built around an old transformer I found and a L296P switch mode IC. It gives me about 0.5v to 38v. Tip: The L296P (and many others) has a 5v internal reference. To make it adjustable down to 0.5v I used an op-amp to amplify the feedback by 10, so at 0.5 v the feedback is 5v.

I have a dual supply which gives 15v, 12v and 5v on one output and 15v, 12v and 3.3v on the other. This is built from the insides of 2 15v wall worts and 4 adjustable SMPS I bought on Amazon for about £5 each.

I have a 13.8v supply which also has a 5v output. This is based on some 13.8v wall worts I bought for 50p each years ago.

I also collect wall worts. I have boxes of them in the loft. Friends and family know that if they are chucking out some old electronics to save me the wall wort. Most of them I'll never use, but if I need one then generally I already have one of the right voltage somewhere in my collection.

I have a 0-30V 5A variable power supply. Use it all the time. I also have an assortment of other fixed voltage PSUs and battery packs.

I have one good DMM and a load of cheap ones all over the house/workshop/garage etc. Even very basic DMMs are pretty good these days and I find being within easy reach is more important than the specification for most purposes.

I also own an old 30Mhz dual-channel Hameg oscilloscope and assorted probes. It used to be fairly useful when I was building audio gear but for digital stuff I've used it maybe 3 or 4 times. Unless you're very rich or really keen on technical toys I personally wouldn't bother.

Steve

ardly: You have not needed a scope and I admit I was wondering if perhaps I would just be getting a costly toy, but I am sure I would learn a lot from it.

So that was my point. The one I detailed above is surprisingly capable and it is extremely small and portable, requiring only a "wall wart" power supply. In fact, the most recent occasion on which I needed a portable scope to check out an immobile piece of digital equipment (actually - a wind organ!), it suited the job perfectly.

ardly: My plan was to get the bench power supply first as that way I could make projects that require a range of different voltages. You built your own power supplies but that means you obviously have a lot more knowledge than me. Buying a supply reduces safety concerns and also I am more interested in digital than analogue electronics. It seems that a 0-30V 5A supply can be had for around $60 USD which does not sound too bad.

So, "more interested in digital than analogue electronics" then. Which means 5 V and 12 V fixed supplies, and for low currents and more than one device at a time, the "wall warts" fill the bill just great.

My variable supplies are only ever used for voltage testing, not for operating digital modules, so their limited current (of the order of 1 A) is adequate. Annoyingly, my one "bench power supply" with the two meters, purchased new, proved faulty and - I haven't bothered to repair it.

PerryBebbington: I have a dual supply which gives 15v, 12v and 5v on one output and 15v, 12v and 3.3v on the other. This is built from the insides of 2 15v wall worts and 4 adjustable SMPS I bought on Amazon for about £5 each.

I have a 13.8v supply which also has a 5v output. This is based on some 13.8v wall worts I bought for 50p each years ago.

I also collect wall worts. I have boxes of them in the loft. Friends and family know that if they are chucking out some old electronics to save me the wall wort. Most of them I'll never use, but if I need one then generally I already have one of the right voltage somewhere in my collection.

And that was exactly my point.

I second the idea of building you power supplies. But do you frequent thrift stores and garage sales, etc? I recently needed a small transformer to provide power to an Arduino nano irrigation control box. I went to one local thrift store and discovered they has several nice looking unidentified fixed voltage power supplies for $5.00 each and an adjustable PSU for $10.00. I bought the two fixed, thinking one or the other would have an appropriate transformer. Neither did, so I have two more power supplies under the work bench.

Paul

A DSO should have a bandwidth of at least 10x the frequency of the square wave you want to look at. This is because a square wave at, say, 10MHz, consists of a series of sine waves of specific frequency and phase. So there is a 10MHz primary, then odd harmonics. If you capture up to the 9th harmonic, it is a pretty good approximation of a square wave.

Of course, you don't usually need to look at the 16MHz clock signal on your Arduino. But you will be looking at other signals that are derived from it.

And to be more accurate, the DSO bandwidth should be at least 10x the highest frequency content of a rectangular wave.

So a 10kHz PWM signal at 50% duty cycle will have the 9th harmonic at 90kHz. But at 1% or 99% duty cycle, the highest frequency content will be the 9th harmonic of 1MHz due to the very short pulse, or 9MHz.

This is why I consider those kit DSOs to be nothing but toys as the commonly have a bandwidth of 100kHz or less.

Also, the capture rate should be 5x the bandwidth, or faster. Yes, I know, Nyquist sampling theorem, but that is for a sine with no higher frequency content. You will be looking at complex waveforms. And the bandwidth is the point at which response starts dropping off and is down by only -3dB.

In commercial DSOs, it is common to find the sampling rate to be 5 to 10 times the bandwidth. You know if they could get away with more bandwidth, they would.

What Nyquist Didn't Say, and What To Do About It

I would not bother with less than 2 channels. In fact, 4 channel DSOs have come down to under $400, it just doesn't make sense not to save up a little more and get one. I bought the Rigol, buy the 50MHz model and apply a firmware change that makes it 100MHz bandwidth because the hardware is exactly the same. $350 for four channels and four probes. https://amzn.to/2zWh3OM

Oh, yeah, watch out for that little piece of c##p the DSO203 that everyone claims has "72MHz analog bandwidth". Some marketing wonk took the specification for 72Msps sampling rate and called it bandwidth. The real bandwidth for it is about 3.5 to 4MHz. My calculations and Electronic Design News tests agree on that. Not bad, but limited to square waves at 1/10th of that.

Knowing that, the latest one shares a 144Msps sample rate between four channels. So 36Msps at 3.5MHz bandwidth is just about right. Fine for the Arduino's analogWrite() PWM function that runs at 490Hz or 980Hz, depending on the particular model of Arduino. Or for audio. Forget troubleshooting a switch mode power supply with it, though.

With a bench supply never chose one without knobs to turn for voltage and current limit, any touch screen or push-button interface is very clumsy by comparison. Analog meters are much more intuitive than digital as you want to see how the current is changing, not stare at a bunch of rapidly flickering digits.

Digital displays are fine for measuring stable voltages, but when using a supply you need to know about changes and fluctuations, for instance sudden jumps or steps in current as supply voltage is gradually dialled up usually spells trouble and you need to know about it (usually parasitic oscillations cause this).

My ideal bench PSU would have analog and digital readouts of course, and one of the digital readouts would be power, and it would have power limiting mode as well as current limiting, and go upto 100V and 20A, but thats all going to cost lots and lots. 30V and 3 to 5A is commonplace and pretty versatile for many things.