Another Scout Project

[Monkeh]

Sorry....I've been AFK trying to stem the flood of tears after that cruel, hard insult from Monkeh....

My eyes are not so good. Even when they're not full of tears....

Sorry.

The LED's certainly don't go out, but they may well dim a bit!

Interesting. Either the current is below the resolution of the meter, or the pulsing is too fast for the update rate.

 

[JohnW2]

The LED's certainly don't go out, but they may well dim a bit!

Hmmm. If they are still producing a reasonable amount of light, I find it hard to believe that the current is not high enough for your posh meter to measure it (my £5 one can certainly do 1μA) - so either there's something wrong with the meter or else it can't cope with the flashing. What sort of rate of flashing are you seeing?

Kind Regards, John

 

[securespark]

Rapid changeover from red to green.

No hang on... is it green to red? I'm not sure...

Lowest setting on meter.

http://isswww.co.uk/Multimeters/Metrel/Alphatek-TEK265-Pocket-size-DMM-with-back-light/

 

[Monkeh]

On 200uA it's likely overrange. I hadn't checked what LEDs you were using, I thought we were still discussing hilariously marginal setups.

With a 3V cell and those LEDs, try the 20mA range.

Those LEDs should have built in current limiting already, and are probably running around 7-12mA. Those are actually fine on a single 3V cell (in parallel, two or three if you're lucky. series will almost certainly fail).

 

[JohnW2]

On 200uA it's likely overrange.

Indeed - but I would then have expected this 'posh' machine to display something other that 'zero'!

With a 3V cell and those LEDs, try the 20mA range.

Indeed.

Those LEDs should have built in current limiting already, and are probably running around 7-12mA.

One might have thought so, but ....

...These very attractive LED's can be used with 3V lithium batteries without the need of resistor (tested with CR2032 for many hours without a single bulb to burn). ... For other types of batteries at least 1ohm 1/4W resistor should be connected in series, but for higher voltages you should search for "LED resistor calculator

Kind Regards, John

 

[Monkeh]

On 200uA it's likely overrange.

Indeed - but I would then have expected this 'posh' machine to display something other that 'zero'!

Have you looked at it?

With a 3V cell and those LEDs, try the 20mA range.

Indeed.

Those LEDs should have built in current limiting already, and are probably running around 7-12mA.

One might have thought so, but ....

...These very attractive LED's can be used with 3V lithium batteries without the need of resistor (tested with CR2032 for many hours without a single bulb to burn). ... For other types of batteries at least 1ohm 1/4W resistor should be connected in series, but for higher voltages you should search for "LED resistor calculator

Kind Regards, John

Mm. I suspect that's because the electronics (and internal resistors) are suitable for around 3V. It.. might survive higher voltages with the external resistor.

This is why I buy known parts, not eBay specials.

 

[JohnW2]

On 200uA it's likely overrange.

Indeed - but I would then have expected this 'posh' machine to display something other that 'zero'!

Have you looked at it?

Yes, but the link provided doesn't tell one very much (except that it's the same colour as my cheapo one!). Even for ~£5 one gets an indication of 'over-range' (not just a misleading 'zero'). Measuring a current of 229 μA...

Untitled

• JohnW2
• 31 Oct 2013
• 1

Kind Regards, John

 

[Monkeh]

On 200uA it's likely overrange.

Indeed - but I would then have expected this 'posh' machine to display something other that 'zero'!

Have you looked at it?

Yes, but the link provided doesn't tell one very much (except that it's the same colour as my cheapo one!). Even for ~£5 one gets an indication of 'over-range' (not just a misleading 'zero'). Measuring a current of 229 μA...

Untitled

• JohnW2
• 31 Oct 2013
• 1

Kind Regards, John

*shudder*

Put the poor thing out of its misery.

As an aside, regarding burden voltages, one of my meters:
uA 1k
mA 12R
A 1R

And another:
uA 51R
mA 2R
A <0R1 (did not null leads, ~0R05 likely)

And a Fluke 87V (via calculation):
uA 100R
mA 1R8
A 0R03

The real numbers for my meter might line up with the Fluke for mA/A, but I didn't null the leads (and wouldn't believe the results anyway for the A range without Kelvin measurement)

 

[JohnW2]

*shudder* Put the poor thing out of its misery.

I'll have you know that's done many years of perfectly satisfactory work, despite usually being under a heap of heavy tools at the bottom of a toolbox (a place that I wouldn't keep an instrument which was worth anything!)!

As an aside, regarding burden voltages, one of my meters: uA 1k, mA 12R, A 1R

That's not dissimilar from my cheapo one (I didn't mention the 10A range before - which, like yours, is 1R).

And another: uA 51R, mA 2R, A <0R1 (did not null leads, ~0R05 likely)

That's pretty impressive - is that a 'posh' /expensive one?

I must have a play with some of my less cheap ones later, and see if there is any pattern

Kind Regards, John

 

[Monkeh]

*shudder* Put the poor thing out of its misery.

I'll have you know that's done many years of perfectly satisfactory work, despite usually being under a heap of heavy tools at the bottom of a toolbox (a place that I wouldn't keep an instrument which was worth anything!)!

It still needs to be killed with fire.

And another: uA 51R, mA 2R, A <0R1 (did not null leads, ~0R05 likely)

That's pretty impressive - is that a 'posh' /expensive one?

Pretty generic low-mid market off-brand meter, actually, with exceptionally **** terminals (I need to get around to resolving that problem). Paying a little extra (this is £30-50 area, from real sources, not ripoff UK retailers) can go quite a ways.. the other is a better meter in every way, though, same price range.

I must have a play with some of my less cheap ones later, and see if there is any pattern

Any based on an FS9922 should be similar to my lower readings.

 

[JohnW2]

I must have a play with some of my less cheap ones later, and see if there is any pattern

Any based on an FS9922 should be similar to my lower readings.

I guess that's the point. There are so few chips (or families of chips), or equivalents, around that I imagine that nearly all the 'standard' DMMs out there will fall into one of a very small number of different specs - and it doesn't necessarily follow that spec and price will always correlate as well as one might have expected.

I respect and sympathise with your viewpoint, but (provided they are 'safe') the cheapest and nastiest are probably perfectly adequate for electricians or electronic hobbyists - and even safety is usually, these days, not an issue for the latter (different from my youth, when 'electronic hobbyist' could sometimes go up to 1500V, or even more )

Kind Regards, John

Kind Regards, John

 

[Monkeh]

I respect and sympathise with your viewpoint, but (provided they are 'safe') the cheapest and nastiest are probably perfectly adequate for electricians

Not even close for electricians. Missing features (low input impedance mode, useful low resistance measurement), ruggedness, a complete lack of safety (I can make your little yellow things explode in quite a few different ways..)..

or electronic hobbyists - and even safety is usually, these days, not an issue for the latter (different from my youth, when 'electronic hobbyist' could sometimes go up to 1500V, or even more )

Well, that very, very much depends what you're doing as a hobbyist. I need the ability to at least roughly measure capacitances large and small (much greater range than the cheapies), decent current capability (both my meters will do from 10nA resolution up to a full 20A range, but as before, there are severe limitations on the lower ranges due to burden voltage), at least reasonable low resistance measurements (FS9922 need not apply. Ever.), fast continuity (FS9922 again need not apply), true RMS response for AC, and the ability to not blow up when poking things which hurt (The -2.5kVDC rail in my scope comes to mind, and direct rectified mains is always fun).

E: Topic, what topic?

 

[plugwash]

mmm, there are some pretty nasty horror stories out there about what happened when cheap multimeters either failed or were accidentally misused (e.g. using wrong sockets or wrong settings) arround systems that could deliver high currents.

http://www.eevblog.com/forum/chat/why-multimeter-safety-matters/

If you are using multimeters arround mains on anything like a regular basis and/or you are using multimeters at all arround systems with higher fault currents than a normal domestic system then I would STRONGLY reccomend both a good quality multimeter and a set of approved fused test leads.

 

[JohnW2]

Not even close for electricians. Missing features (low input impedance mode, useful low resistance measurement), ruggedness, a complete lack of safety (I can make your little yellow things explode in quite a few different ways..)..

I obviously meant as a supplement to an MFT or whatever, but I agree that many of the cheapos probably have some potential safety issues. As for ruggedness, I'm not so convinced - as I said, that one I pictured has survived vast amounts of ill-treatment over the years.

Well, that very, very much depends what you're doing as a hobbyist. I need the ability to ...

Sure, I suppose I should have said 'average hobbyist', or something like that!

... and the ability to not blow up when poking things which hurt (The -2.5kVDC rail in my scope comes to mind, and direct rectified mains is always fun).

As I said, I would imagine that the great majority of current-day 'electronics hobbyists' never meet (in that context) a voltage greater than about 24V

However, I'd never argue with the desirability of having the best tools and equipment that one can afford, and whose cost one can justify in terms of intended usage.

Kind Regards, John

 

[Monkeh]

Not even close for electricians. Missing features (low input impedance mode, useful low resistance measurement), ruggedness, a complete lack of safety (I can make your little yellow things explode in quite a few different ways..)..

I obviously meant as a supplement to an MFT or whatever, but I agree that many of the cheapos probably have some potential safety issues. As for ruggedness, I'm not so convinced - as I said, that one I pictured has survived vast amounts of ill-treatment over the years.

I admit, their lack of weight makes them remarkably resistant to falling damage. If you open them up, though, you may well find the input terminals are on a separate board which is only connected by a solder bridge. Which is.. well, let's just not go there.

However, I'd never argue with the desirability of having the best tools and equipment that one can afford, and whose cost one can justify in terms of intended usage.

Kind Regards, John

Indeed, and personally, I believe £40-50 on a reasonable DMM is a sound investment for anyone who intends to use one more than once a year.