Electronics > Beginners

Power supply advice please (I live in the UK)

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bd139:

--- Quote from: nfmax on December 07, 2018, 05:06:34 pm ---
--- Quote from: bd139 on December 07, 2018, 02:21:17 pm ---Warning on the Farnell supplies. The E/LT ones are missing a couple of essential diodes, one across the pass transistor and one across the output.

--- End quote ---

That's odd - are you sure? I have a couple of these, one L30-1 and one LT30-1. The circuit diagram, issued 1979-07-28, shows 1N4003's in both places, D202 & D203. Maybe it was missing in earlier incarnations of the design? Mind you, a 1A diode is a bit wimpy for a 1A supply, especially when they use two paralleled 2N3055's as pass transistors.

Nice supplies, and the only ones I have at present that go up to 30V.

--- End quote ---

There are a few revisions, not all documented well. Many an hour head scratching there. You have to crack it open and look. It doesn’t necessarily not span later versions as I’ve seen some of the plastic fronted late ones without diodes!  :palm:

rstofer:

--- Quote from: tggzzz on December 07, 2018, 12:21:23 am ---There's a good argument to be made that if you can't specify what you need and why, then you don't need it.

--- End quote ---

Exactly right!

I often see the suggestion to get some kind of power supply right away.  Gee, I got by without one for decades!  Most of my stuff was 5V and I had a fixed 5V 3A power supply.  Wall warts work, even simple 78xx and 79xx supplies work.  If I was playing with transistor amplifiers, I might use a 12V wall wart.

I did buy a Rigol DP832 but only because I could, not because I NEEDED it.

So many projects these days revolve around Arduino that are USB powered so I wonder why people buy triple output supplies.  Yes, they are great for older dual-rail op amp projects and that's exactly why I bought mine.

Think through the PS issue carefully.  You may find that this can be deferred for a very long time.

The Hakko FX888D soldering station should work well.  You do not need a hot air tool until you try to desolder BGA packages.  Everything else can be desoldered by cutting the leads and removing the tabs one at a time.  I have a hot air tool and don't use it.  I don't desolder much of anything.  If you want to remove and replace a component without cutting the leads then a hot air station is required.  Buy one when you need it.

As to SMD soldering, when you get that far, you might consider converting a toaster oven.  Post another thread...

You can solder small SMD projects on a kitchen hot plate.  Place the board the plate, crank the  knob to high and use tweezers to remove the board after the solder flows.  Then turn off the heat.  Not a bit of science or math is used for this process.  Cook to done, remove from heat!  Obviously, the plate must be in complete contact with the board.  Some hot plates don't work well for this.  I saw a link yesterday talking about putting a table saw blade over the heater to spread the heat.  Sounds good!

The Rigol DS1054Z scope is very inexpensive, has built-in decoding and, when unlocked, is rated for 100 MHz.  It's a great scope for the money.  I have one but I also have an older 350 MHz Tek 485 that sits under my bench taking up space.  I have a very few applications where I need anything even approaching 100 MHz so the Rigol is fine.

What about an arbitrary waveform (signal) generator?  There are some cheap kits around.  Maybe they are adequate.

================================

Here's the thing:  What do you want to learn?  That question isn't as dumb as it seems.  Do you want to become the next great op amp guru?  That's a different skill set than the world's best Arduino programmer.  There are probably differences in the toolset as well.

If you're starting from nowhere, I recommend you buy the Analog Discovery 2 and use all of the tools it provides.  There is no other investment of an equivalent amount of money that provides anywhere near the flexibility.  Nothing even comes close!  I would use the external wall wart to augment the power supplies of the AD2.  If I was playing around with dual rail op amps, I would build a small +-15V power supply.  One amp goes a long way with op amps.  The idea that 30V 5A times 3 supplies is somehow required is just ludicrous.  A 450 watt project is a space heater!  And that doesn't account for the losses...

DMM - you need a couple, maybe 3.  I'm going to recommend the Aneng 8008 because it is inexpensive and super accurate.  Dave did a video just search for something like 'eevblog aneng 8008 video'.  These are around $25 so they won't break the bank and they have some interesting features - like a signal generator and frequency counter.  There are better meters but you can get them later on.  Usual warning:  Don't trust the CAT ratings and don't play around with mains voltages.

If you want to do lab type experiments to learn electronics, there is no better tool anywhere than the Analog Discovery 2.  The thing is, people look at the pretty little box, giggle a bit, and blow it off as a toy.  Huge mistake!

Where else can you get a dual channel scope, dual channel arbitrary waveform generator, 16 bits of digital IO that can be used as a logic analyzer and serial stream decoder plus the software to do neat things like generate Bode' Plots of analog circuits?  It's one thing to pencil whip a low pass filter, it's quite another to see the actual output versus frequency.  That's real learning!

Which brings us back to "what do you want to learn?".

tggzzz:

--- Quote from: rstofer on December 07, 2018, 07:38:28 pm ---
--- Quote from: tggzzz on December 07, 2018, 12:21:23 am ---There's a good argument to be made that if you can't specify what you need and why, then you don't need it.

--- End quote ---

Exactly right!

I often see the suggestion to get some kind of power supply right away.  Gee, I got by without one for decades!  Most of my stuff was 5V and I had a fixed 5V 3A power supply.  Wall warts work, even simple 78xx and 79xx supplies work.  If I was playing with transistor amplifiers, I might use a 12V wall wart.

--- End quote ---

Just so.

It was a little bit of a mental wrench when I realised I could buy and use a general purpose PSU!


--- Quote ---As to SMD soldering, when you get that far, you might consider converting a toaster oven.  Post another thread...

You can solder small SMD projects on a kitchen hot plate.  Place the board the plate, crank the  knob to high and use tweezers to remove the board after the solder flows.  Then turn off the heat.  Not a bit of science or math is used for this process.  Cook to done, remove from heat!  Obviously, the plate must be in complete contact with the board.  Some hot plates don't work well for this.  I saw a link yesterday talking about putting a table saw blade over the heater to spread the heat.  Sounds good!

--- End quote ---

I use a (dedicated) cheap saucepan with a glass lid. The lid helps keep the heat in so the topside components aren't cold, and the glass allows you to see when the flux evaporates and the solder flows.

I also use a layer of sand in the saucepan, to spread the heat and prevent hotspots, and to allow the temperature rise to be more controllable.


--- Quote ---Here's the thing:  What do you want to learn?  That question isn't as dumb as it seems. 

--- End quote ---

It isn't remotely dumb. In fact it is one of the touchstone  questions: your answer shapes whether you go this way or that way.

Finding the right question is usually more difficult than answering it - and more important.


--- Quote ---If you're starting from nowhere, I recommend you buy the Analog Discovery 2 and use all of the tools it provides.  There is no other investment of an equivalent amount of money that provides anywhere near the flexibility.  Nothing even comes close!
...
Which brings us back to "what do you want to learn?".

--- End quote ---

Yes, and yes.

Also remember that each and every tool has a learning curve. If you choose wisely, the tools help you learn and explore electronics. If you choose poorly, the tools help you learn which specific button to press in this version of this tool.

In that respect, old analogue scopes are better than digitising scopes, since they are simpler and all the controls are on the front panel, not hidden in a menu system. But if you have a digitising scope and can use it, that isn't a reason to get a working analogue scope.

rstofer:

--- Quote from: tggzzz on December 07, 2018, 08:48:30 pm ---In that respect, old analogue scopes are better than digitising scopes, since they are simpler and all the controls are on the front panel, not hidden in a menu system. But if you have a digitising scope and can use it, that isn't a reason to get a working analogue scope.

--- End quote ---

Having used my DS1054Z, I see many advantages over my Tek 485.  In fact, the only thing the 485 brings to the dance is bandwidth.  Bandwidth is cheaper when buying used analog scopes.  For the Arduino style projects and reasonable < 100 MHz projects, a 100 MHz digital will be excellent.  Four channels is more than twice as good as two channels.  This shows up quickly when working with SPI transactions.

If I were just learning and tending to roll around like a BB in a bowling alley, I would go for the AD2.  It's easy to say that while having two of them and having used them off and on for several years but, were I a student, that's the way I would go.  My lab is in my backpack alongside my laptop and slide rule.  OK, programmable graphing calculator with networking and Computer Algebra System (CAS).  These kids have it easy!

I do a lot of modeling with LTspice and MATLAB.  I also do a lot of code weenie work with Fortran and C.  My Microsoft Surface Book is probably my most important tool.  I use a more powerful desktop for Xilinx Vivado but the Book is adequate for everything else.  One way or another, a PC of some type is becoming a required tool.  Especially for embedded projects.  BTW, a Bode' Plot looks pretty good on an attached 27" monitor!

Electronics is played in a very large sandbox with many areas of interest.  Just find a corner and dig in!

CJay:

--- Quote from: rstofer on December 07, 2018, 07:38:28 pm ---
--- Quote from: tggzzz on December 07, 2018, 12:21:23 am ---There's a good argument to be made that if you can't specify what you need and why, then you don't need it.

--- End quote ---

Exactly right!

I often see the suggestion to get some kind of power supply right away.  Gee, I got by without one for decades!  Most of my stuff was 5V and I had a fixed 5V 3A power supply.  Wall warts work, even simple 78xx and 79xx supplies work.  If I was playing with transistor amplifiers, I might use a 12V wall wart.

--- End quote ---

Well to be far, you did get a PSU right away, it just wasn't variable.

A PSU of some sort is essential, doesn't matter if it's batteries, a fixed supply, home made or bought, it all depends what's available in your budget/needs, as tggzzz says, you have to be able to define your needs.

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