Total Electronics novice would like a little help. - Page 1
Forum section: electronics / beginners

author: Chuckles
author_rank: Newbie
timestamp: November 20, 2021, 07:58:28 pm
content: Hello AllI'm totally new to this site.Have now retired and always wanted to find out a little more about electronics so thought now would be a good time to learn.I have treated myself to a decent bench power supply and after watching some of Dave's videos a good oscilloscope. (TTI PL303, R&S RTB 2002 200 meg)My main question for now and after watching Dave's video on the subject I'm very concerned I may blow up the scope. (shorting back to earth with scope probe)I do not intend to be going near to mains/high power.Could someone please explain if I can cause damage with much lower voltages?At the moment I want to carry out some practical work with a Arduino that is powered via my power supply the TTL PL303. I know I could use a battery in this case but pointless having a decent power supply and not using it. Dave's video mentioned using a isolated power but I cannot find anything (not that I really know what I'm looking for). I do know the scope and power supply must be earthed.If some kind person throw a bit more light on the subject I would be very grateful.Please excuse my stupidity.Thanks

author: Benta
author_rank: Super Contributor
timestamp: November 20, 2021, 08:17:12 pm
content: You'll be OK.Generally, lab power supplies have floating outputs. If connected correctly to your mains supply (three prongs/wires on the plug), the case will be connected to PE (protective earth).The same is the the case for your oscilloscope, except that the BNC connectors will also be connected to PE.So using those two together will not give any problems. The problems arise when you try to measure something on mains connected equipment. In short: don't do that.Enjoy your new hobby

author: Chuckles
author_rank: Newbie
timestamp: November 20, 2021, 08:48:11 pm
content: Many thanks for your fast reply.Beginning to panic after more spending more than I should.

author: wizard69
author_rank: Super Contributor
timestamp: November 20, 2021, 09:18:43 pm
content: Quote from: Chuckles on November 20, 2021, 08:48:11 pmIt is not a bad idea to go slow if you are new to electronics. Generally low voltage is not a problem.One thing that can raise your confidence is to follow a basic electronics program. Look for the old Navy NEETS program, freely downloadable from the internet.

author: rstofer
author_rank: Super Contributor
timestamp: November 20, 2021, 10:57:38 pm
content: Congratulations on retirement. I've been doing it for 18 years and don't spend a moment thinking about going back to work.The thing to remember about the scope is the dangling ground clip on the probe. You need to be careful where you connect it. You won't have a problem with a decent power supply because the outputs are floating unless you jumper them to the ground jack (usually provided on the panel). I would also recommend working with batteries because they are definitely floating. On Arduinos I use the Gnd pin for the connecting point and on other circuits, it will be apparent where ground is located.You can always measure between where you plan to connect the lead and an earth ground. There should be little if any voltage. Experiment: Ground one side of your power supply (I would do Black to Green) and measure between the other side (Red) of the supply and the BNC on the scope. You should see a voltage. Then disconnect the ground jumper and think real hard before you ever use it again. There will be occasions where it is necessary but they are rare.And, as mentioned above, stay away from mains until you have a good deal more experience. And then you will stay away BECAUSE you have a good deal more experience. Trust me, I did not jab my Rigol probe in an AC outlet to see what would happen to the scope! Even if I saw something weird on the scope, what could I do about it? It I can't fix it, why bother knowing about it?There are lots of folks around here willing to help. Different people have different interests so somebody will chime in no matter where you go.

author: Shock
author_rank: Super Contributor
timestamp: November 21, 2021, 08:22:38 am
content: Think of the ground clip on an oscilloscope probe as the "shorting lead". Anything you attach it to will short to ground (mains earth). If there was a difference in voltage potential, current will now flow down that path. If that current is too high, damage will occur.When starting out it helps to study schematics and identify supply voltages, grounds and common points of a circuit. Watch the first part of this video until you understand it. They are trying to sell active differential probes, but a floating power supply (or battery), isolation transformer or differential measurement using two channels are also valid, just pros and cons to each method.

author: nigelwright7557
author_rank: Frequent Contributor
timestamp: November 21, 2021, 08:27:39 am
content: I accidentally connected my scope ground to a mains bridge rectifier and it just blew out the circuit breaker.The main soft spot with scopes is the inputs.Most have max voltage written on scope near input or its in the manual.Some el cheapo ebay USB scopes can only cope with +/- 5 volts so you have to make sure your probes are set to x10 or x100 depending on what you are looking at.

author: nigelwright7557
author_rank: Frequent Contributor
timestamp: November 21, 2021, 08:31:01 am
content: Quote from: Chuckles on November 20, 2021, 08:48:11 pmYou can pick up low frequency scopes for £20 ish on ebay.They are fine for audio frequencies but for high speed stuff useless.Bear in mind with digital scopes that mega samples need to be divided by 20 or 30 to get max frequency you can see on screen. so a 20Meg samples scope is good for 1mHz wave.Some scope specs are very ambitious ? It takes 20-30 dots to see a nice waveform.

author: rstofer
author_rank: Super Contributor
timestamp: November 21, 2021, 04:07:22 pm
content: The OP has a very nice scope with the additional feature of 200 MHz bandwidth. That is a great scope!I have often thought that if we can use a 9Mohm resistor in the 10X probe portion of the signal path why we couldn't add 100K Ohm in series with the dangling ground lead. Even with a complete screwup on 240V, only a couple of mA would flow over the ground path. At lest for an initial look at the circuit. The added resistor wouldn't add much to the attenuation compared to the 9Mohm inside the prove on 10X.Another idea: Buy a pair of 200 MHz 10X FIXED probes and leave the 1X/10X probes in the drawer. My Analog Discovery 2 has a limited voltage input so 10X probes prevent a potential screw-up. ProbeMaster.com 4905-1 is a fixed 10X 250 MHz probe and lists for $55. You can get a nice kit with 3 probes and a bunch of accessories with a carrying case for $182.50https://probemaster.com/design-your-own-4900-series-master-probe-kit/Yes, it's a lot of money but not nearly as much as that R&S scope!I have no idea how any of this translates into the UK.

author: m k
author_rank: Super Contributor
timestamp: November 21, 2021, 04:26:53 pm
content: Quote from: Chuckles on November 20, 2021, 08:48:11 pmNot so far ahead and you start liking precise numbers.You can take some back then.

author: rstofer
author_rank: Super Contributor
timestamp: November 21, 2021, 07:02:16 pm
content: OP, you're going to need a signal source. Before you invest in something expensive, like the Siglent SDG2082 (which I have), you can search Amazon for 'cheap signal generator' and you might turn up something like:https://www.amazon.com/1HZ-500KHZ-Functional-Generator-Frequency-Counter/dp/B07WFT3679Not a great generator but good enough for beginning.Then grab a couple of transistors and follow along with w2aew's videohttps://youtu.be/zXh5gMc6kyUThere's a lot of education in that video! It isn't important to grasp the subtle details, just watch how he manipulates that scope. Although not specified, a 2N2222A or 2N3904 transistor should work. Basically any transistor described as 'small signal' and NPN. Amazon has a large assortment of kits. The devices are likely 'floor sweepings from China' but they should work for this simple test. Just search Amazon for '2N2222'. Lots of choices. Maybe search for 'resistors' while you're there:https://www.amazon.com/BOJACK-General-Purpose-Transistors-Assortment/dp/B07T61SY9Yhttps://www.amazon.com/BOJACK-Values-Resistor-Resistors-Assortment/dp/B08FD1XVL6You also need some capacitors like:https://www.amazon.com/BOJACK-Ceramic-Capacitor-Assortment-Capacitors/dp/B07P7HRGT9And, yes, you will need breadboards and jumpers:https://www.amazon.com/Breadboards-Solderless-Breadboard-Distribution-Connecting/dp/B07DL13RZHhttps://www.amazon.com/AUSTOR-Lengths-Assorted-Preformed-Breadboard/dp/B07CJYSL2Thttps://www.amazon.com/Elegoo-EL-CP-004-Multicolored-Breadboard-arduino/dp/B01EV70C78Dave has some great "Fundamentals Friday" videos and w2aew's videos are always well done.

author: rstofer
author_rank: Super Contributor
timestamp: November 21, 2021, 07:35:31 pm
content: That 3M breadboard used in w2aew's videos is considered the Cadillac of breadboards. It is pretty pricey at $60 but it will avoid the inevitable head scratching that WILL occur when using cheap breadboards as linked above.https://www.digikey.com/en/products/detail/3m/922306/180285DigiKey carries the entire line:https://www.digikey.com/en/product-highlight/3/3m/300-series-solderless-breadboardsI decided to buy myself an early Christmas present. I have been using the cheap breadboards far too long.

author: RJSV
author_rank: Super Contributor
timestamp: November 24, 2021, 02:55:28 am
content: Yes, that suggestion of buying a couple (cheap) educational kits is good; also don't forget there are cheap toys having speakers, motors, LEDs, at local drugstore. The surface mount transistors generally resemble 2N2222 or 2N3905 outputs, and toy motor controllers feature 'H' bridge outputs.In cheapo toys, you often get push buttons and optical sensors / transistors for your parts bins.I kept buns of various AUDIO connectors and stereo cables, but that's old school, now.Today, my parts bins have all kinds of multicolor LEDs and LED utility lights, on timers etc.

author: RJSV
author_rank: Super Contributor
timestamp: November 24, 2021, 11:51:02 pm
content: Took a picture, to show how I got a PLANETARY gear thingy...and that salvage part, taken from a broke car RC toy. Box said ages 6+.One drug store sells a wired up remote 'puppy'. That thing features dual polarity controls, and an audio board, (for barks).Your experiments might be strictly electronic, but many (of us independents) need mechanical expertise, more or less. That's why so 'excited', to see that PLANETARY GEAR set...Heck: I don't know even how to use that little work of art (pls see picture).A beginner? Try send me a PM with reasonable question, the forum helped me, so...

author: RJSV
author_rank: Super Contributor
timestamp: November 25, 2021, 01:39:32 am
content: I think one of those responses was referring to ISOLATION TRANSFORMER:Those are special, some look roughly like a Variac, in that the medium power devices have a regular mains AC outlet, for plugging your device to under test. It is, for example in the US, 120 VAC both for input and for output; that is, that isolation transformer is simply wound as a one to one turns ratio. You get NO voltage change, with only modest power capability (small ones maybe 200 watts).But advantage is that the secondary (transformer) windings are voltage-isolated. That gives some increased measure of 'safe' isolation. Of course, that's a great, fairly affordable way to go, when repairing stuff, generally. Bench TECHs use an isolation transformer, just for one-time or temporary use.Reminded me of some older friends, (now gone), engaging in self-employed 'COLOUR TELEVISION' repair / service folks.Try search on 'Isolation Transformer'

author: Doctorandus_P
author_rank: Super Contributor
timestamp: November 25, 2021, 05:14:49 am
content: I'd say forget about isolation transformers for a few years.Just keep away from mains voltages and teslacoils and other stuff like that for a few years, and then let your projects grow with your experience.

author: nigelwright7557
author_rank: Frequent Contributor
timestamp: December 21, 2021, 09:25:40 pm
content: You can spend a absolute fortune on test gear and tools.1/ Second hand scope, had it for 10 years £45 off ebay.2/ Simple soldering iron, had about 10 years £13.3/ USB PC oscilloscope £25 off ebay, not fast but good enough for audio.4/ Signal generator, £20 off ebay.5/ wire snips from CPC £1.50