Also, with regards to resistors in the supply one thing to be careful about is adding resistors in the supply or ground lines to the chip. The best source for a digital or analog circuit is a very low impedance DC source. I have seen technicians try to reduce noise from the oscillator or other sources in the circuit by adding a resistor in the Vcc. But the noise will only increase even if you try to use a butterworth configuration. I would recommend as a rule of thumb never increase the supply impedance. ----- Original Message ----- From: "Lee Jones" To: Sent: Saturday, April 24, 2010 9:11 PM Subject: Re: [OT] Ohms law , beginners question ... > Jason wrote: > >> So I need no resistor on my delicate microcontroller ? wrong ! >> About 2 weeks ago I thought that might be true. I tried it on >> one of my chips , it released it's magical smoke and burned up > > Instead of 2000 people on this list guessing at what you mean, > maybe you should provide a detailed description of the circuit > or a schematic drawing of same. > > You do not need a resistor on the supply or ground rails of a > microcontroller. You may or may not need a resistor on other > pins -- either input or output. Frequently you need way more > than a single resistor -- either multiple resistors, capacitors, > inductors, other active components (i.e. transistors, etc). > > No one here can advise what you need unless you tell us what > you are trying to do. > > On Sat, Apr 24, 2010 at 5:07 PM, Rich wrote: > >>> A device will only draw what it is rated for. If you have a >>> device that is rated for 5 volts at 5 mA and you connect it to >>> a source that is rated for 5 volts at 1000 mA your device will >>> only draw 5 mA because of its load impedance. One cannot push >>> current through a device; a device draws current according to >>> its load impedance. > > Rich's statement is correct. This statement would generally > refer to the Vdd (5V supply rail) on a microcontroller. If you > don't believe it, then you need to learn more about basic > electronic circuit theory. > > Lee Jones > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist