Buying components early on.

[trys]

I read somewhere that some people are more susceptible to dying from electrical shocks that others.  I think I'm immune but damn does it hurt.

My favourite is 50Hz AC mains.  It hurts like hell but you just can't let go.
BE WARNED KIDS THE FIRST SHOCK CAN AND DOES KILL!  DO NOT PLAY WITH THE MAINS.

Many many years ago, I read or heard somewhere:

"Volts jolts, and Mills kill"

(The "Mills" referring to milliamps).

I've had two electric shocks in my life. Both were my own stupid fault, nobody else's.

One was building a variable PSU using a LM317T (about thirty or more years ago). It was an incredibly useful kit. I brushed the back of my hand past the live fuse connector.

Luckily enough it was the back of my hand, so my hand clenched and got away from it (a muscle will stay contracted towards an AC shock).

One tip with mains is to do all "hot" work one-handed (keep one in a pocket) so that if any current does pass it's less likely to pass through your heart and stop it. The other one is to pre-plan all the steps. The best tip of all is to avoid doing it.

As a result, it put me off mains work (until last week, 30+ years on) to build my second PSU project. I've built it and it will stay built, I'm not going to fiddle with it any more. I promise.

Trys

[SkrillBill]

When you buy components from say digikey or mouser, add a couple extra of the part you want and throw in a couple of others. Over time, you'll build up a decent stock of parts. Another way you can acquire parts (and practice desoldering) is by removing parts from old PCBs. Power supplies, oldder radios, really any pcb with through-hole components. This is what i did / still do and it works out pretty good. You will eventually have to buy something, so always make it worth the shipping. Someplaces even have free shipping above $xx.xx, so if you can afford it build up a cart to that amount to get free shipping.

[bd139]

Also with parts, if you can afford to wait a couple of weeks, these guys are pretty good: http://www.taydaelectronics.com

Stick to the royal ohm resistors though; the other ones are spindly shit - rest of the parts are good!

If you stick $100 worth of stuff in an order it'll fly through customs with a pre-printed jiffy bag with "$7 commercial samples" on it 

[nes999]

As the creator of said sticky my advice, even though I did not take it at the time I asked for it, limit your stock.

Personally, when I have an idea I simulate first. LTSpice and TINA is my stockpile.
For must solve today, I've never grabbed anything but caps, resistors, the odd diode and a transistor. I currently only keep a small selection of these in THT.  Everything else I simulate, order some parts, wait a day or two, test, design a prototype,order PCB wait two weeks and build.

For an intermediate and advanced kit, check the listing for Art of Electronics. Will probably showcase everything you need to know. I find every 'simulation works, why not my prototype then' valuable.
I'm still a beginner, always will be I think.

I just ordered the art of electronics. It was a pricey bugger!

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[Brumby]

It's all these little things that add up.

Yeaaaah.

Do yourself a favour .... don't add up what you spend over a year.  Your workbench will never seem to reflect the value of what you've put into it.


+1 on not "stocking up" on parts you hope will be useful.  Last week I came across a tube of 7400 (not HC or LS - just regular TTL) from more than 30 years ago ... and that's just one example.

[trys]

I just ordered the art of electronics. It was a pricey bugger!

Good book. Get the other lab one too.

[KL27x]

Very few things you would want to stock up on. Over the course of some years, you may find you move from thru hole to smd. From logic chips to micros (and micros to newer micros). Everything you stock up on is potentially (more like probably) garbage to you in the future. There is very little that you will be happy to have on hand. In Digikey's warehouse, it has value. In your possession, it is just junk that will be thrown away when you die, if not sooner. It's like how a car loses 20% of its value as soon as you drive it off the lot, except it's more like 99%.

[nes999]

I just ordered the art of electronics. It was a pricey bugger!

Good book. Get the other lab one too.

What is the lab one?

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[thermistor-guy]

When you buy components from say digikey or mouser, add a couple extra of the part you want and throw in a couple of others. Over time, you'll build up a decent stock of parts. Another way you can acquire parts (and practice desoldering) is by removing parts from old PCBs. Power supplies, oldder radios, really any pcb with through-hole components. This is what i did / still do and it works out pretty good. You will eventually have to buy something, so always make it worth the shipping. Someplaces even have free shipping above $xx.xx, so if you can afford it build up a cart to that amount to get free shipping.

Yeah, I do this. I scavenge parts from broken gear before throwing it out, if it's not economical to repair. Connectors, terminal blocks, heatsinks, ceramic spacers. Unusual components or materials that are rated for high power, high voltage, or high temperature. Useful materials like Mylar film or copper sheet. Cables and fasteners from old PCs, useful for building and modding new ones. Magnets from failed disk drives, for magnetizing the tips of screwdrivers (handy when repairing laptops). 2.5 mm and 3mm dia. shafts from old DVD drives, useful as accurate punches for sheet metal, to make temporary housings.

There is a wealth of technology in the stuff people throw out.

[ChrisLX200]

I would hazard a guess that most folk are limited by space anyway, certainly I am, so I could not store a large selection of components even if I wanted to. I have a good mix of parts recovered over the years from scrap PCBs, some enclosures, a lot of logic ICs (which have never been used for anything other than experiments), switches, connectors and so on. I have recently topped off with a few new electrolytic caps, and some SMD collections (cheap and don't take up much space). I figure I'm in a good position to tackle repairs for the most part without needing to wait for a parts order.

[bd139]

Very limited space here as well. I have two small CPC boxes and a couple of binders of parts and that's it. All the loose stuff is compacted in ziplock bags.

I don't bother recovering anything these days as it takes up too much space now on the off chance that I might need some of it. When I eventually drop dead, I don't want my family to have to clear out a hoarder. I'd rather just order some new bits of RS for next day

[woody]

50Hz AC mains.  It hurts like hell but you just can't let go.

I know that there's a nice T-shirt quote in there somewhere 

[woody]

So I had to look up "Jesus stick"

https://www.urbandictionary.com/define.php?term=jesus%20stick

I certainly hope you mean something different

[paulca]

I work with 3 parallel banks of 8P2S 8uF, 4kV caps (totally 96uF, charged to 7.5kV, 2.7kJ). I treat them like death himself.
I have a normally closed fail safe relay for slow discharging, a manual 100Ohm fast discharging rod with long handle, and for the worst case, a Jesus stick.
I was bitten by 33nF, 25kV once, and a couple times by up to 100nF, 1kV, and once by 47uF, 300V. I don't plan to dump 2.7kJ through my body, though.

Ouch.  I'm not sure how many uF a 15" CRT has in it's tube charge caps but it certainly hurt and as it's DC it threw me clean across the room and left me shaking.

It's worth adding to my warning:  "EVEN WHEN ITS OFF!"  as a lot of main gear has got large caps inside and so even if it's switched off and unplugged when you open it there are still VERY dangerous potential currents in there you could unwittingly unleash on yourself.... and the hurt a lot.

On an aside and in defense for "don't buy cheap chinese rubbish".  I have got a shock off a PC power supply after unplugging it.  I literally switched it off at the PSU, switched the mains off and pulled the plug, then I promptly got a rather unexpected and sore shock off the Live/Earth pins on the plug, spark and all.  I gather they did not have reverse protection on the power caps and that allowed my hand to discharge them to earth.  Dodgy.

[paulca]

So I had to look up "Jesus stick"

https://www.urbandictionary.com/define.php?term=jesus%20stick

I certainly hope you mean something different

What will you shout if you just shorted a huge capacitor and turned a few kJ of energy to acoustic energy and a bright flash?

Can you get a Holy good f**k stick?

[alanb]

We get shafted for the £3.95 charge as well. If you spend £20 ex VAT it's free though. Farnell are next day (sometimes UPS screw up but that's rare)

CPC-Farnell have free delivery on orders over £5 (3-5 day)
You can get next day with a payment of 2.99 +Vat

[nes999]

I volunteer at a dog obedience school and I also do the majority of their maintenance. I was changing out a fluorescent light fixture. I shut off the breaker, power to the ring is cut. You should have seen the other volunteers when a cloud of sparks rained down. It was get power from somewhere, just not enough to light anything.



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[paulca]

So the stuff all arrived.  "Mail bag!", LOL

I even created a box with resistors laid out by size. 
10R, 100R, 1K, 10K, 100K, 1M
22R, 220R, 2K2, 22K, 220K
47R, 470R, 4K7, 47K, 470K
Assorted others.

Also built the trigger comparator for the 555 and was somewhat surprised and a little disappointed that it worked first time!  When a bit of code I spend 2 hours writing works on the first run I feel similar surprise, disappointment and a moderate amount of suspicion.  I'll do the other one on Saturday.

One thing I bought of theBay that is invaluable I find, is a "Nail painting light".... relax I'm not painting my nails, it's just a circular flourescent with a 8X magnifier lens.  Makes reading ICs and fiddling with breadboards so much easier.

[paulca]

Feeling pretty good with myself as I got the full 555 timer circuit working.  Learnt quite a bit as me, the instructions and my understanding of them parted company once the individual sub circuits were built.  I had to work it out bit by bit by retesting each component, finding a few things backwards and finally tinkering until annoyingly surprisingly the LED started to flash.

It's mickey mouse stuff, but for me this is my first circuit involving more than a few components.

Next project might be replacing the comparators with op amps.  Haven't worked out what I can replace the flip-flop/latch with yet. 

Can anyone suggest a basic logic IC with at least one flip/flop or SR latch on it?

[bd139]

Nice one 

I'd get a couple of 74LS00's (they are just 2-input NAND gates) and learn how to build a couple of different types of flip flops first. There are quite a few with different characteristics. You could get 74HC00's but they are CMOS and therefore a little easier to blow up just by looking at them funny.

Then move to 74LS74 which is a D-type flip flop.

When you start with this you will need "debounced" switches as inputs.

[TheDane]

Buying components early on can be tricky.

Passives are a must to stock. Unfortunately there's a ton of different kinds, once you get into it. (Filters for one, fast and slow blow fuses, poly-fuses, multiples components into one device/arrays, different physical sizes and leaded/smd, power ratings, voltage rating - don't use a 50V rated tantal cap in a 5V circuit - that can be bad as it self-heals when voltage ratings are correct, crystals and oscillators can have different load values and of course frequencies, etc.)

Active devices can be really hard; you can stock up on e.g. leaded components - and when you do a layout you learn there's no room, so you have to go SMD - or choose a different version, with different pin layouts. A 5V device that runs 16MHz, but running at 3v3 it will only run 5MHz and so on. Easy to miss in the datasheet when quickly glanced over - it's usually hidden far from page 1/2.

Stock also grows 'x-tra' legs, and tends to disappear on its own over time. You know you have had it, but now it' gone, not to be found. 

Then there's the supplier New Featured Product Update Announcements, telling you that there's a new part which is much better, smaller, cheaper, etc. Hard not to keep using what you have, and not adding to your already growing stockpile.

Doing homework, reading datasheets and comparing various manufacturers can be a lengthy process - and it can take up more time than 'just doing the design' and buying all combined + a few items extra most likely to blow up during testing and development.

Waiting, trial and error, stock issues and other not so fun stuff can make the homework worth it though.
Usually having some R&D stock for developing, and then down-scaling for production is a good idea.
Some companies also require you to have 2.nd sources on everything, if not 3 sources. Then you go by inventory, and take the fight ONLY when you absolutely need the new item.

The best thing, I found, is that you know the ins and outs of the devices if and when you use them. Buy lots, and you become an expert on that device. Then they go obsolete, and you're in for some more schooling/shopping.

Happy shopping and reading - its a never ending story 

[trys]

I just ordered the art of electronics. It was a pricey bugger!

Good book. Get the other lab one too.

What is the lab one?

The lab one is called "Learning The Art of Electronics" "A Hands-On Lab Course" by Thomas C Hayes with the assistance of Paul Horowitz.
ISBN 978-0-521-17723-8

Excellent gook. It can be read independently of The Art of Electronics too.

Trys

[paulca]

I'd get a couple of 74LS00's (they are just 2-input NAND gates) and learn how to build a couple of different types of flip flops first. There are quite a few with different characteristics. You could get 74HC00's but they are CMOS and therefore a little easier to blow up just by looking at them funny.

Interesting.  I ordered x5 of these, then I looked up an SR Latch and realised it was made from NOR gates.  I ordered some NOR gates... then I realised that the 555 timer latch is (?) active low and probably should be NAND gates.  Aww well I have both now anyway, whichever way it works out.

Then move to 74LS74 which is a D-type flip flop.

The D FlipFlop requires a rising clock pulse.  I found this quite profound to use a 555 timer to control a gate in a 555 timer circuit.

When you start with this you will need "debounced" switches as inputs.

As above, again I could get recursive and use a 555 timer in monostable mode to debounce the switch


Is there a useful cheat sheet for selecting the common/beginner logic gate ICs?  I thought I could simply look for the 74LS range, but it turns out it's not that simple.  It seems that searching for these on CPC etc can lead you down a rabbit hole or ending up purchasing an expensive IC for more specific requirements when an IC a tenth the price was available elsewhere.

[bd139]

TTL Cookbook by Don Lancaster is the goto book for this stuff. There's a ton of databooks available but they're all rather large and unwieldy.

You can make any gate with NAND gates

[paulca]

You can make any gate with NAND gates

Yes, but you can also slide down a concrete slope in your underpants.  It's entirely possible but not very comfortable

In a Computing HNC I did we had to power a single 7 segment display from a 4 bit number using only NAND gates.  I think it ended up with 30 or 40 gates.  (I prefer  Ben Eater's approach of using an EPROM lookup table)