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Electronics => Electronics => Topic started by: krich on January 15, 2009, 06:06:49 PM

Title: SMD Resistor Code
Post by: krich on January 15, 2009, 06:06:49 PM

Am I reading this code correctly?  The SMD resistor is marked with R01, so that would be 0.01 Ohms, right?

I'm guessing it's probably a current sense resistor because of the low Ohms, but I would expect it to be a bit larger, really...  It's about the size of a 1208 package.

Title: Re: SMD Resistor Code
Post by: Soeren on January 17, 2009, 10:43:01 AM

Hi,

Why would it need to be larger?

Title: Re: SMD Resistor Code
Post by: TrickyNekro on January 17, 2009, 11:20:29 AM

well... reading SMT resistor is easy as hell... you are right about the value...
But.... well... 1208 is quit big.... if I'm right it's almost 1W!!! or a little bit less....
What is it powering???

Title: Re: SMD Resistor Code
Post by: Webbot on January 17, 2009, 07:08:20 PM

Surface mount resistor have three numbers: the first two digits being multiplied by the third. The third digit represents how many zeros after the first two. For example a surface mount resistor with code 1-0-5 would mean that the first two digits (1-0) would be multiplied by 5 zeros. To give the value 10 00000ohms or 1Mohm.

The same coding is also used in surface mount capacitors. Capacitor are similar to the above but the base number is pF or pico farads. eg a capacitor labeled 2-2-3 has the value of 22 000pF.

Title: Re: SMD Resistor Code
Post by: krich on January 18, 2009, 12:57:18 AM

The background behind this is that I'm going through some of the scrap circuit boards that I have laying around and one item that I was looking for in particular is a Current Sense Resistor.  These are typically super low value and (I think) somewhat larger than normal resistors...at least the ones I've seen before (DALE resistors mainly in 32XX and bigger packages).  Usually find them in or near a power supply.

Anyway, I'm looking for this resistor for an L298 motor controller that I'm building.  That's a 3A H-bridge IC if I remember correctly, so I'm concerned about the "wattage" of the resistor.  Probably going to be running at least 7.2V, but perhaps up to 12V, to drive the motors.  Haven't done the math on it yet, but I am concerned that a "1Watt" resistor isn't going to cut it unless this thing is truly down around 0.01Ohms.  I have yet to see sparks fly on my bench, and I don't want to start.   ;D

I've got the SMD resistor code down just fine.  It's just the odd codes like this one that have me second guessing myself.

Thanks guys!