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Essential Measuring Instruments for the Newcomer.

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Sulaiman

Sun Oct 04 2009, 09:15PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3141

Essential
1) Cheap dmm, preferably two.
2) Oscilloscope.
Very useful
3) Variable power supply.
4) Mains filament lamp to put in series with mains powered circuits for initial testing.
5) Signal generator.

A second hand 'scope is cheaper than many electronic toys/gadgets and it's resale value is about what you paid for it. (Christmas present?)
Doing electronics without a 'scope is like biology without a microscope, astronomy without a telescope, music without an instrument etc. etc.
Without it you're just guessing, seeing waveforms gives a 'feel' for what is going on.

Beginners should stay away from moving coil meters; too easily damaged and the load that they put on circuits often gives false results. If you really need the analogue function get a dmm with a bargraph display.

One caveat .. I don't trust cheap dmms for high voltages.
Make a resistive divider and use a low voltage range.
Apart from that the 'safety' (if any) of a Fluke or similar comes mainly from using fused probes. We destroy quite a few Flukes where I work - usually physical damage, not electrical, their ruggedness is NOT proportionate to their cost vs. cheap dmms.
Personally I have a GBP2.99 dmm and a GBP9.99 dmm with RS232 interface for data-logging etc.

Once you have a dmm and a 'scope you can make your own power supply and signal generator, though usually second hand (eBay) units are cheaper than the cost of parts.

If you continue in electronics you will inevitably end up with loads of equipment, but what type will depend on your own particular area of interest.

Proud Mary

Sun Oct 04 2009, 09:29PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Sulaiman makes a very important point about a power supply. Over and over we see people's early projects stumble because they simply don't have the amps to power it, sometimes even hoping to power a flyback setup with a wall wart.

A variable PSU is extremely useful, but absolutely not essential for those who just want to get going, and can't buy all these lovely instruments and facilities at once.

For many of the popular beginners projects, like the flyback generator, even a rather run down old car battery will provide 100 times more current than a regular wall wart, and is perhaps the best way for someone starting out to make a high current supply on a small budget. True, you're stuck with 12V, but a car battery can deliver a 100 amps for fifteen minutes or so, whilst a hundred amp supply could be very expensive indeed.

Sulaiman

Sun Oct 04 2009, 09:44PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3141

I've actually 'standardized' my projects to run from a 12 V battery supply where practical.
Partly due to their low source impedance, also for portability, low electrical noise, independence from the mains supply and my interest in amateur radio.
A battery charger is of course also required.

Bjørn

Sun Oct 04 2009, 09:54PM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

If you have a PC power supply you get -12V, -5V, 3.3V, 5V and 12V. If you add a 7805 regulator and a potentiometer you also get a 0-10V supply. Make an adjustable voltage divider between -5V and 5V and connect the GND pin of the regulator to that and you get 0-10V output. The most difficult bit is to figure out what kind of load it needs to regulate properly and add a suitable resistor.

Proud Mary

Sun Oct 04 2009, 10:15PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Sulaiman wrote ...

I've actually 'standardized' my projects to run from a 12 V battery supply where practical.
Partly due to their low source impedance, also for portability, low electrical noise, independence from the mains supply and my interest in amateur radio.
A battery charger is of course also required.

What a pleasure to have such a complete endorsement from yourself, Sulaiman! If I knew even half as much as you about our subject, I should count myself a lucky fellow!

Frosty90

Mon Oct 05 2009, 02:15AM

Registered Member #1617 Joined: Fri Aug 01 2008, 07:31AM
Location: Adelaide, South Australia
Posts: 139

Also in terms of power supplys you can often 'improvise', I have a small transformer I run with a variac for 0 to 17 AC, and a big old MOT i run in reverse with the variac for 0 to 40 AC. Also I like to use small transformers as chokes in series with the mains instead of fillament lamps, but only because i have them handy I suppose.

Cheers
Jesse

Proud Mary

Mon Oct 05 2009, 04:43AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Frosty90 wrote ...

Also in terms of power supplys you can often 'improvise', I have a small transformer I run with a variac for 0 to 17 AC, and a big old MOT i run in reverse with the variac for 0 to 40 AC. Also I like to use small transformers as chokes in series with the mains instead of fillament lamps, but only because i have them handy I suppose.

Cheers
Jesse

That's the stuff, Jesse. Except for the wealthy few, our hobby is all about improvisation to try and put together for a few bucks what might cost hundreds if you had to buy everything ready made.

Of course, if you stick with the hobby for donkeys years, as many of us do, then in the end you have get to have more test equipment and spare parts than you know what to do with (one of the reasons I am always giving stuff away to other 4HV folk!

) but Rome wasn't built in a day, and it takes years to get a really first rate set of instruments together for most folk.

We've talked a lot about multimeters, ranging from the cheap n cheerful to the costly Flukes, but everyone seems to take it for granted that once you've got your meter you know what to with it, how to use it strategically to analyse circuit functions, and locate even complex faults.

Take the common, "My ZVS isn't working, what shall I do?" question which comes round without fail every couple of weeks. It's hardly possible to make a simpler circuit, with so few parts, and the strategic use of the meter in combination with the figures from data sheets should make it immediately apparent what is going wrong - my point being that whilst almost here everyone here has a meter of some sort, not so many have any clear idea how to use it in the analysis of a circuit, and the identification of fault conditions, which is what the meter is all about!

Ah ha, the Mission to Explain!

Nicko

Mon Oct 05 2009, 09:17AM

Registered Member #1334 Joined: Tue Feb 19 2008, 04:37PM
Location: Nr. London, UK
Posts: 615

Coffee. Lots.
Life insurance.
Understanding SWMBO.

Actually, I like test kit - here's one end of my workshop -

- The class A 400W/chan amp on the desk idles at 60C, so is ideal for keeping coffee just right...

Keeping on track, you will see a Tektronix DMM916 multimeter on the left of the desk - brilliant meter - last one that Tek made before they pulled out of the market. Great true RMS meter with AC+DC offset cabability.

Get a cheap meter for when you think you might blow something up - bricking 200+ buck meters and other kit is painful - use cheap-as-chips kit to make sure you're in the right territory, then home in with the good stuff...

Proud Mary

Mon Oct 05 2009, 09:22AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

What a lovely set up, Nicko! Where do you do all the drilling and sawing and cutting and brazing - have you a separate construction bench?

Nicko

Mon Oct 05 2009, 09:30AM

Registered Member #1334 Joined: Tue Feb 19 2008, 04:37PM
Location: Nr. London, UK
Posts: 615

Harry wrote ...

What a lovely set up, Nicko! Where do you do all the drilling and sawing and cutting and brazing - have you a separate construction bench?

Its changed a bit since that photo - I passed the nice Tek 7000-series scope on to a college, and the Tek digital storage scope has a problem at the moment (PSU capacitors), but I now have some very nice HP RF synthesisers & audio analysers. I replaced the big clunky logic analysers (there are two in the photo) with a small USB jobbie that is wonderful and lives in my laptop case.

An old photo of the other end of the workshop (its different now) is at

- the outside is

. Basically, its too small - the middle bit (with the mini-lathe, saw bench etc.) is so full of "stuff" that I actually have to do a lot outside...

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