on 29/12/01 12:42 AM, Keith Christopher at keithc_21211@YAHOO.COM wrote:

Hi Keith,

> Question for the list, when setting up a circuit, how
> does one know when to use a capacitor _vs_ a resistor

I'm not quite as new as you, but pretty new.

Have you had any background in electronics? It depends what you want to do.

With Micros, resistors are generally used as "pull-ups" or "pull-downs" -
ie; you use say a 4K7 or a 10K resistor to "pull-up" an input to the
positive (VCC) rail, then you can use a switch or other device to "pull" the
input to ground. You can also do it in reverse - use the resistor to pull
the input low (to the ground rail), then have the switch or othe input
device pull the input high.

Resistors are also used for current limiting (ie; driving LEDs, transistors
etc) and a capacitor/resistor combination can also be used as the cheapest
form of external clock.

Capacitors are used to filter your power supply (large electrolytics) and
smaller ceramic caps can be used to filter noise from your inputs and are
necessary to be used in conjunction with external crystals, reset circuits
etc.

My best advice I can give you is to buy some books - projects books for the
PIC would be preferred - and study the schematics and read why certain
components were chosen and/or not used and apply these rules to your own
circuits.

Hope I have been of some help.

Regards,

Sean

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