It would seem to me that Xiao Xu's idea of 1 ohm serve two purposes and is better than a 10 ohm. First, Xiao Xu's idea that it reads directly is good because a digital meter cold be easily connected, but secondly it is always best with regards to noise immunity and stability to use as low an output impedance from the power supply as possible. ----- Original Message ----- From: "Olin Lathrop" To: "Microcontroller discussion list - Public." Sent: Wednesday, May 26, 2010 12:10 PM Subject: Re: [EE] Current measurement using 1Ohm resistance > Sarin Sukumar A wrote: >> i put a 1Ohm resistance in series with the supply voltage and measured >> voltage generated across it. >> My circuit is working well, that means it gets enough power. >> So the voltage across 1Ohm resistance indicates the current drawn by >> my circuit. >> I just want to know is this method right or wrong? > > It's fine. That's essentially what your multimeter in current mode does. > It's a voltmeter with a current shunt accross it. The shunt value is a > tradeoff between getting enough voltage to read accurately versus dropping > too much voltage and having the current meter affect the circuit. > >> Then whenever i powered on the circuit i saw peaks of voltage across >> 1 ohm resistance initially, That means it draws high current in the >> starting moment. > > Yes. > >> Why is it like that? > > Charging up power supply caps, most likely. There can be other reasons > too. > >> From this measurement i get 200mV that means my circuit draws 200mA, >> isn't it? > > Yes. > > > ******************************************************************** > Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products > (978) 742-9014. Gold level PIC consultants since 2000. > -- > 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