Thursday, September 16, 2010

Reference voltage

Not enough digits to show 4.096!

What's that? You say!

It's a reference voltage IC working! Courtesy, in the interest of science, of Texas Instruments, that was kind enough to spare me some dollars and sent me for free one of "REF2940" IC. They have several versions with different output voltages but I chose this one (4.096V output) because it's a round number in binary that could be handy for calibrating or making comparations using an ADC (analog to digital converter) chip.
By having this reference voltage source I can now verify the acuracy, in voltage terms, of my equipments. With a precision and calibrated resistence I can then calibrate current meter equipment (it can be done using only a voltage reference),

By having calibrated instruments one can have more confidence in the results measured and that's specially true when most RF measuring equipment is expensive as hell and you have to build your own.
This is in no way an replacement for a serious calibration situation just an amateur solution....remember, professionals built the Titanic!

The assembly is easy, except that the IC itself it's the size of an smd resistor, nowadays every litle thing comes in smd... the IC pinout is as follows:

If your are accessing this page in say 1280*1024 resolution (in a 19" monitor) the IC is the size of the word "RE" in the above picture...whell... maybe a litle smaller :)

Here's the table of dropout voltage vs load current which is nice to print and put outside the equipment box (when it's ready, after this prototype stage).

The simple schematic follows... +5 V are provided by a little 7805 not in schema.

And the prototype (can you spot the IC? :)

It's in the intersection of a strait line from the end of the crocodile claw and an horizontal line from the body of the 7805 (the big black dot).

Have fun and "calibrate" your equipment.

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