From: email@example.com (N. Thornton)
Subject: Re: How to make/solder a circuit fast?
Date: 23 Sep 2002 04:56:22 -0700
References: <firstname.lastname@example.org> <email@example.com> <3D85221F.5D187DCE@texas.net> <firstname.lastname@example.org> <3D864834.email@example.com> <firstname.lastname@example.org> <email@example.com> <firstname.lastname@example.org>
NNTP-Posting-Date: 23 Sep 2002 11:56:22 GMT
email@example.com (The little lost angel) wrote in message news:<firstname.lastname@example.org>...
> On 21 Sep 2002 16:42:25 -0700, email@example.com (N. Thornton) wrote:
> >So no scope. Do you not have a piezo bleeper? theyre only 20 cents,
> >they make horrid bleeping noises in lots of things these days, so
> >they're not hard to find lying about. They're very handy for seeing
> >whats going on in circuits.
> I've never heard of a piezo bleeper but take it to be some kind of
Yeah, little 1 inch wide 1mm thick resonant speakers, with sound
quality good enough for bleeping. Usually brass sheet with a piezo
disc glued on one side. Almost anything that bleeps has one.
> Though given that the PSU's main output is switched at
> something like 100Khz ~200Khz, wouldn't any noise be out of human
> hearing frequency?
The fan doesn't run straight off the main supply output tho, it goes
thru a separate speed controller. And given the fan's siginficant
inductance, there's a good likelihood that may be audio freq PWM. If
the fan is run on 100kHz, then you'd be quite right... unless youre
closely related to a bat :) They can hear 100kHz.
> >PC scopes are free, as are very old PCs that will run the software. A
> >486 and an old ISA sound card is all thats needed, with Win 95 or 3.1.
> >95 needs 12M RAM.
> hehehehe, the same reason I didn't go for a PC scope is due to the
> frequency needed. These are all limited to a max of 96Khz for the best
> soundcard I can find.
Very useful nonetheless. And it'd only cost you a soundcard. They also
have no response at dc, they'll go down to around 20kHz.
With a bit of thinking one can do a great deal with primitive tools. I
remember when I needed to fix something and had no multimeter with me,
so I just used lightbulbs instead. :)
> Unless you know where I can find a working scope for less than 100USD?
They do turn up, probably auctions. But there are reasons people put
things in auctions.
> >Another way to distinguish is to see if theres a differnce between
> >average fan supply V and peak V. A moving coil meter will give you
> >average V. A 1k R then a diode supplying a 1uF capacitor wouild give
> >you the peak voltage, which can be measured wi digital or moving coil
> I only have digital scope, would it not measure average V? Is it
> because digital scopes samples the voltage so it only reports what it
> see at that point in time? But wouldn't this mean for a PWM signal,
> the DVM would see different voltage each time?
Yup, thats one of the problems with digital meters. As you say, they
don't usually measure average, but just measure snippets. An analog
moving coil meter actually gives significantly more information than
your usual DVM.
Course you can easily make a lash up analog meter: almost any moving
coil meter would do, even a little miniature 1" one. put an R in
series, and just compare peak and ave V to see which is greater.
> >With a dc supply, peak V will be 0.6v below average, due to the
> >diode's V drop. With PWM supply, ie a chopped dc supply, Vpeak should
> >be around 12v, V ave maybe 6v.
> That wouldn't be too bad right? Since I've got a 5V regulator at the
> very start of the whole chain that can handle up to something like
> 24V~35V (sorry spec sheet somewhere else ATM).
A fan motor is wire wound, so its inductive. If its driven off a PWM
supply, it will produce an inductive kick voltage every time the
supply goes off, lots of times per second. And that kills LEDs. Thats
the possible problem.
> >You can just take your chances of course, or you can test it.
> I'll try to find a way to see the part number on the IC for the fan
> driver (is this the correct way to use the term driver?).
Indeed :) It drives the fan.
> Just have to
> figure out how without ruining the whole thing. :D
Aww, spoil sport! :)