EEVblog #168 - How To Set Up An Electronics Lab

[torch]

The outputs are floating right now. There are a couple of ground points that rely on the chassis to sink some caps and the heat sinks back to the mains ground, but none seem to be tied to the output negative. The current limits do not appear to be adjustable, although there does seem to be some sort of short-circuit protection (for the power supply, not the load of course) and the power must be removed to reset it -- sounds like a polyfuse, but I can't read much off the devices down between the heatsinks.

Hey, what do you want for $6? 

[alm]

I won't claim it's bad value for the money, was just trying to assess how well it would do as a bench supply. I expected the negative rail to be connected to the safety ground, so that's a positive .

You will need some additional parts (eg. case, jacks/binding posts, current measurement DPMs / power indicators) to make it into something approaching a bench supply.

[nukie]

I have moved house three times in my life and I find it gets better everytime I build my lab. If you are not moving, well you can start by pulling down everything and start all over again. That is if you have the time and money. I am not kidding, small improvements can only be made to existing setup, starting a fresh gives you freedom and new idea.

Don't just go out there and buy whatever that is mention here unless you are trying to do a combined shipping. There are essential items and some are not so 'needed' so make your own decision wisely. When buying tools for once off use, you can get the nastiest, cheapest of all but if you are using it more than twice then buy something you can afford.

The video didn't talk about the workdesk/table much. So lets have a look.

There are several plans on the www in regards to building heavy duty carpentry desks, have a look at those if your work involves hammer. Building your own desk is exciting and rewarding especially when you can customize it's size to your liking.

If you are not doing anything that involves hammer, a cheap table will suffice, as long as it will support your equipment. You want something deep if you have roomspace. This is because the equipment can take up space and you will be left with reduced work area. If you have access to IKEA then I strongly suggest those height adjustable leg so that you can raise your table closer to eye level so you don't have to do hunch back while working on SMD circuits. This is similar to a watchmaker's desk but not as high. Reduce your fatigue especially working long hours. Don't forget a gas strut height adjustable chair to complement the desk.

Higher desk surface means there's plenty of space between the underdesk and your laps. You should consider a thin sliding drawer, for storing items such as solder wire, wick, tweezers, pliers, cutters, small items etc. This reduce clutter on your desk and a drawer under your table means quick access to your most frequently used tools. Use storage to keep the mess out. You can also have a multilevel drawer that sits under the desk if you have space but I find it better to have a bin there for rubbish.

If your growing out of space for test equipment, it's time to build a desk shelf. If you have a long desk, one or two supports in the middle is good to prevent droop. Some people like to place their desk close to the wall so they could build a wall shelf instead. I personally prefer a desk shelf so I could move my desk along with my equipment.  Tek oscilloscope can be quite heavy so place them on the desk rather than the shelf. Place the power supply closest you and DUT, so you don't run long supply wires and introduce extra resistance in the circuitry.

[torch]

You will need some additional parts (eg. case, jacks/binding posts, current measurement DPMs / power indicators) to make it into something approaching a bench supply.

Yup. Bought a box when I got it -- the bloody project box was 3x the price of the project! -- and have been tinkering with bits and pieces I had lying around:
.
You can see where I added another heat sink for the LM317 in an empty area of the board on the upper left. I need to buy a green binding post for the mains ground and I've ordered a pair of mini digital readouts off eBay for the variable output. The pot is temporary, I'll get a 5K 10-turn like Dave recommends (there's another shockingly expensive item!). All I had handy was a used 56K linear, so I'll have to change the resistor too. You can see where I plan to cut out for the readouts -- I decided to wait until I had them to confirm the dimensions. So the mains ground, negative and variable + posts are on the left, then fixed +12, +5 and +3.3 outputs on the right.

I don't think this can ever compare to a good quality bench supply. But I think it will compare favourably to the first one Dave shows in the video.

If you are interested, here's the underside where I goobered in the LM317. I did not add caps -- I tried with and without on the breadboard and it didn't make any difference. The green wire from the ADJ is run to a conveniently unused pin on the header for the pot. You can see one of the chassis mount ground points in the picture -- I will run a wire around and pick them all up, taking them back to the mains ground because the box is plastic. The two blobs of solder all by themselves are just to hold the heat sink steady.

[saturation]

Its too bad some good posts are made on the blog page, because they aren't as easy to search.

Its amazing that so many end up having the same tools or type of tool as the comments suggest.  I have pretty much 80% of nearly identical stuff as Dave, excluding new acquisitions like the Rigol or the Atten hot air station.

http://www.eevblog.com/2011/04/30/eevblog-168-how-to-set-up-an-electronics-lab/#comments

One thing I'll add is consider salvaging electronics from your local trash.  Extracting parts with a hot air station is very convenient.  Many of are full of US, Taiwan or Japan ICs or transistors of highest quality.  Many ICs are often still in the catalog, and obsolete ones the spec sheets are often locatable on pdf.

[ciccio]

I'm new to the forum, but reading the previous posts I did not find any reference to three really useful tools.

The first one: a Variac (variable auto transformer): it is mandatory when working on audio power amplifiers or power supplies: you can slowly ramp-up  line voltage and see what happens, without fear of blowing big electrolytics or expensive power transistors, you can see at what voltage your  regulator circuit begins to hum, etc.
Mine is a museum piece: I assembled it in a "suitable" case about  30 years ago, and never finished the job, so the power switch is the mounted the wrong way: on down.
Inside there is an hefty 2.5 amps ISKRA variac, made in the former Yugoslavia. Don't remember how the AC voltmeter is made, maybe with some sample converter.
You can buy cheap Chinese variacs, or you can find a real GeneralRadio on ebay.
 
The second one is a safety tool: it is a switched power socket, with a two-pole switch and a neon pilot lamp.
When I work on mains powered equipment, I tape the power switch of the equipment in the ON position, and rely solely on the outlet switch for on/off: this way I can always see the ON  lamp, even when the equipment indicator in on the side opposite to me.
The box is plugged to a socket that has a combined 10A max - 30 mA  differential resettable protection, separated from the one that supplies the bench tools and the measuring instruments.

The third one is an home-brew version of the "third hand": I simply glue a wooden "clothes clip" (I think it's name is different, but I cannot find it, and the photo is self-explaining) to a piece of scrap sheet metal or to anything that has sufficient weight, and that's all: I have an insulated clip that is heat-resistant, does not damage the surface of the "thing" it's holding, and does not cool the piece I'm soldering,  and it's cheap

[david77]

A variac is a nice piece of equipment, though I prefer the isolating type to the autotransformer variety.

Personally I consider it dangerous to just switch the mains off when working on the insides of a device. It's too easy to flick the switch accidentally and "bzzzzt". I consider it much safer to conciously pull the plug and put it somewhere out of the way, often I sit on it or put it in a pocket.

[ciccio]

Personally I consider it dangerous to just switch the mains off when working on the insides of a device. It's too easy to flick the switch accidentally and "bzzzzt". I consider it much safer to conciously pull the plug and put it somewhere out of the way, often I sit on it or put it in a pocket.

True, but most of the times impractical...This is the reason for having the "switch in the box" sitting on one side of the bench, far from the equipment under observation. The bipolar switch guarantees that both conductors are cut-off, independently of the wiring of the equipment, the wiring of the plug and the insertion of the plug in the socket (sorry but Italian and German plugs can be plugged in both ways)

[vk6zgo]

Personally I consider it dangerous to just switch the mains off when working on the insides of a device. It's too easy to flick the switch accidentally and "bzzzzt". I consider it much safer to conciously pull the plug and put it somewhere out of the way, often I sit on it or put it in a pocket.

True, but most of the times impractical...This is the reason for having the "switch in the box" sitting on one side of the bench, far from the equipment under observation. The bipolar switch guarantees that both conductors are cut-off, independently of the wiring of the equipment, the wiring of the plug and the insertion of the plug in the socket (sorry but Italian and German plugs can be plugged in both ways)

Even with the Australian type of plug,you can occasionally run into a socket which is wired backwards.The correct wiring is a Rule now,but it used to be just a recommendation.
It may be the same with UK wiring,I'm not sure.

From what I read on the Internet,240 volt sockets are becoming a lot more common in the U.S.A. & Canada than they once were.
With a North American 240 volt plug,both sides are "hot"at 120v w.r.t earth,& 240v between them,so a double pole switch would be  essential.

VK6ZGO

[torch]

From what I read on the Internet,240 volt sockets are becoming a lot more common in the U.S.A. & Canada than they once were.
With a North American 240 volt plug,both sides are "hot"at 120v w.r.t earth,& 240v between them,so a double pole switch would be  essential.

240v outlets in the home are pretty rare and specialized over here. Typically the stove and dryer outlets are 240v, but nothing else (hot water heaters, baseboard heaters, well pumps, central air, etc. are usually 240v, but hard-wired). Split duplex receptacles are common, but must be wired such that both halves are fed from the same leg. Exceptions do occur where hobbists install specialized equipment. I have a 240v outlet for my lathe and another for my welder in the garage, but those have unique layouts that cannot be mistaken for (or connected to!) anything else.

What can be a problem is when neighbouring receptacles are wired such that they are fed from opposing legs. If equipment is plugged into each and then interconnected (eg: home theater) some strange things can result. That is certainly something to watch out for when setting up an electronics lab!

[vk6zgo]

Guess I've been reading too much on QRZ.com! 

"Hams" often run 240v outlets in the USA to drive their 1.5kW PEP linear amplifiers,so I incorrectly assumed that they were becoming more generally used.

In Australia we are only allowed to use 400watts PEP!

VK6ZGO

[torch]

"Hams" often run 240v outlets in the USA to drive their 1.5kW PEP linear amplifiers,

I would file that under the "hobbyist installing specialized equipment" category. 

[IanB]

Guess I've been reading too much on QRZ.com! 

"Hams" often run 240v outlets in the USA to drive their 1.5kW PEP linear amplifiers,so I incorrectly assumed that they were becoming more generally used.

It's relatively easy, in principle, to run a 240 V circuit off its own breaker from the distribution panel, especially if the panel is close to somewhere like the garage or basement where you want the outlet and the panel has spare slots. Unfortunately it is not always easy to find a place to hide the wiring since the original wiring was put in the wall cavities when the house was built and ripping out drywall to install or pull new wiring is no picnic.

I have an unused 240 V dryer outlet in my garage, but it is not in a location where I can conveniently use it for anything else without a long additional cable run.

[vk6zgo]

In Oz,of,course,the normal power sockets are 240 volt 10A,so we are well set for using higher power stuff.
We still have a problem installing new sockets (called GPOs here),particularly in Western Australia,where most of the older houses have double brick outer walls,& single brick internal walls,
Cabling is only easily carried out in the cavity of the outer walls.
To run cables on the internal ones means you have to cut slots in the wall & re-plaster,
or live with exposed conduit.
We aren't allowed to do our own,anyway,so I let the Licenced Electrician have the headaches! 

VK6ZGO

[torch]

Here (Ontario, Canada) a homeowner is allowed to do their own electrical in their own home. Theoretically they are supposed to pull a permit and have it inspected by the Electrical Safety Authority, but that very seldom happens unless they are building something new and obvious. Every hardware store carries a wide selection of wire, boxes, etc. etc. etc. Larger ones even carry a selection of panels and ground rods.

[david77]

Same in Germany, houses are traditionally built from brick, that means putting in new wiring is not something you can do easily. Usually only when a major remodeling is planned anyway. There's no law that that forbids you to do electrical installations yourself. The DIY stores carry all you need. Problem is many DIYers do really stupid and dangerous stuff because they think they know what they're doing. I have seen stuff that made my hair stand on end.

[Neganur]

There's no law that that forbids you to do electrical installations yourself.

Don't forget to mention that it has to be approved by a certified electrical engineering master technician (Elektromeister). Saying there's no law that prohibits DIY installation is a bit misleading.

[david77]

Sorry, getting a bit OT but anyway:
Ok, in theory this is true. But what electrician in their right mind is going to sign off some dodgy DIY wiring job? They have to take full responsibility for the job and if something happens they walk to the gallows. So what happens in real life?
Mr & Mrs Doityourself happily continue plastering over speakerwire used for mains and replacing 10A fuses with 25A ones because "they keep blowing all the time" not aware of the consequences, listening to "advice" some underpaid uninformed flunky in a DIY store has given them.
I see that every day and wonder why not more people die.

[torch]

I see that every day and wonder why not more people die.

As a professional firefighter, I see it every day (almost) too. (Sometimes I'm even the reason more people don't die)

I'm especially impressed when they attach the speaker wire to aluminium wiring with marrettes, omit the j-box and bury it in cellulose insulation. 

[david77]

Thank god aluminium wiring is quite rare here, at least in western Germany. Apparently it was widely used in residential wiring jobs in the ex-GDR, though. One can of worms we were spared.

[vk6zgo]

Electrical wiring stuff is widely available in Australia ,too,even though we aren't supposed to do it.

Technicians & EEs who "know what not to do" usually obey the rules & get a Licenced Electrician to do the job,but people
who know nothing leap in & produce some horrific "wiring".

Back in the 1960s,both cables & electrical fittings in Australia made a"quantum leap",with standardisation on
PVC insulation,& plugs made from heavy duty PVC with specified construction methods.
The time since then has been more of incremental improvement rather than great leaps.

The scary thing is,when you are confronted with some of these "DIY" electrical jobs, in many cases they are using cabling that dates to before the standardisation referred to above.
Obviously someone has salvaged 50 year old cable & connectors!

At least the DIYs done with modern standard equipment ,if done correctly,may be safe,but old.perished wiring is unlikely to ever be anything but a deathtrap!

VK6ZGO

[stryker]

Over xmas I finally completed a bench power supply inspired by this video from way back when. 

In hindsight the case I chose was probably a bit on the cramped side, but eventually worked it all out with a grinder and some klingons.  Now I see I should probably swap the black and green terminals on the front (sometime in the next 3 years will do based on progress up to this point).  This is now my 2nd bench supply, and I put one together for a mate.  It works a treat!

Thanks again for these vids Dave.
Geoff

[Ed.Kloonk]

Holy thread resurrection batman

[stryker]

Yes the date on my PCB was from early 2015.  It was too much of a triumph not to post about but