Archive for January, 2010

MAX4173 Current sense amplifier

I just built a current sensing application based on a MAX4173. I am suitably impressed with this device. It is extremely versatile and cheap. The MAX4173 allows you to measure the current across a sense resistor with a 28V common-mode range and provides a ground-referenced output proportional to the current across the resistor. I will probably be using one on most of my projects from now on since I do a lot of prototype work and having a cheap and easy way to sense current draw is pretty useful.


The MAX4173 is available in either an SOT23 or SO8 package, and only requires a decoupling capacitor and a sense resistor to operate. There are three different preset gains available so by combining that with the sense resistor value you can achieve a variety of current ranges.
I used the device in a 4-20mA control loop, with a 20X gain and a 10Ω resistor for a 0.8-4V output into an ATtiny 13’s ADC with a 5V reference. The 10Ω sense resistor is small enough that the loop won’t be affected and large enough to provide good signal range and sensitivity.
For future projects I will probably be using the higher gain version with a smaller sense resistor on the input power line and just leave the MAX4173 output on a header for diagnostic measurement if I don’t have a spare ADC pin. This will limit circuit loading but provide an output for measuring actual circuit current draw.
There is another similar version of the MAX4173, the MAX4080. It can handle higher common-mode voltages and bidirectional current. It’s also a bit more accurate than the 4173, but I haven’t tried it out yet.

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Monday, January 18th, 2010 Electronics 5 Comments

LED backlit desk sign

I was messing around a while ago with my CNC and some of the various engraving bits I’ve tried for routing PCB traces. I had a piece of acrylic lying around, so I made myself a sign for my desk at work. I don’t really have that job title, it’s technically “intern” since I’m doing the college thing; but it would be my title if a job title was based on what you did. The description next to my name in the office’s roster is actually “special projects”, but it didn’t sound as interesting.


I used a NUD4001 constant-current LED driver from ON Semiconductor and some OSRAM SideLEDs. The NUD4001 is really quick and easy to implement as it only requires an external resistor to set the current level. The unit is fused, and powered by a 9V AC/DC wall wart. I tried a couple different colors, but this amber looked the best.

As a side note, I really like using ON semiconductor parts. They have excellent datasheets that usually have really good examples.

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Monday, January 18th, 2010 Electronics 1 Comment