[sdiy] Selecting Components

[Elby Designs]

I would suggest 0.6W 1% Metal Film resistors. Buying in even small volumes 
means the price is insignificant. This way gives you `equal to' or `better 
than' the tolerance you need for most applications. Then you will only need 
to buy the occassional 0.1" resistor or Tempco.

For capacitors I have found it easier to determine the types by their value. 
If they are less than 1nF then usually 50V NPO Ceramic Disc are fine. There 
are a few occassions when you will need to go for Polystyrene but most BOM's 
will usually tell you that. For 1nF to under 1uF I use 100V Polyester. These 
all have the same footprint making the job of pcb design a lot easier. They 
are a good quality component and you won't normally need to go outside of 
that type. 1uF and above are either Tantalum or Low ESR Electrolytics. I aim 
for 16V as the minimum voltage for tantalums and 25V for Electrolytics. This 
helps to keep the sizes reasonably small and consistent. Higher voltages can 
be used in all situations bearing in mind that hey will also be physically 
larger. One exception to the Polyester guide is 100nF capacitors that are 
used for decoupling. For these I will often use Monolithic Ceramics.

I think if you follow these guides you will carry the minimum variety of 
components yet will handlemost projects that come your way.

Best Regards

(Mr) Laurie Biddulph
Mobile: 0400 257 645

Elby Designs
ABN: 70 022 727 605
http://www.elby-designs.com

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----- Original Message ----- 
From: "Roy J. Tellason" <rtellason at verizon.net>
To: "Synth DIY" <synth-diy at dropmix.xs4all.nl>
Sent: Thursday, September 07, 2006 4:37 AM
Subject: Re: [sdiy] Selecting Components


> On Wednesday 06 September 2006 12:57 pm, Ian Fritz wrote:
>> At 10:20 AM 9/6/2006, R. D. Davis wrote:
>> >It depends upon how much power the resistor needs to dissipate... look
>> >to good old Ohm's law for the answer: p = i x e.  If you're buying in
>> >quantity, buy 1/4W ones, if 1/8W is needed, the 1/4W ones will suffice
>> >unless there are space limitations.
>>
>> Hmmm ... Look at it this way:  Consider power as P = V^2/R.  A typical
>> synth situation might be something like 10 V across 10 kOhm.  This is 
>> 0.01
>> W.  Even 10 V across 1 kOhm is only 0.1 W.  So 1/8 W is fine for almost
>> everything!
>
> No they're not,  they're too damn small!  The smaller the part the more
> difficulty I have with these large hands,  not to mention that it's 
> getting
> harder for me to see the damn things!
>
> I can see where for a mfr. it might be worth while switching over to those
> things,  or in some applications where space and weight is indeed an 
> issue,
> but I don't see any reason to go to smaller than quarter watt for any DIY
> stuff.
>
> -- 
> Member of the toughest, meanest, deadliest, most unrelenting -- and
> ablest -- form of life in this section of space,  a critter that can
> be killed but can't be tamed.  --Robert A. Heinlein, "The Puppet Masters"
> -
> Information is more dangerous than cannon to a society ruled by 
> lies. --James
> M Dakin
>