Monday, September 8, 2014

Minima Controller Shield - Some measurements

Last evening I placed my second Si570 on my Minima Controller shield and am pleased to see it is functional as well.

The datasheet for the Si570 CMOS version says that supply current draw should typically be 90 mA with a maximum of 98 mA.  With both devices powered up, I am seeing a current draw on the 3V3 rail of 140 mA.

The Arduino UNO R3 board uses a TI LP2985-33DBVR regulator which according to its datasheet is rated for 150 mA.  There is nothing on the Arduino board that uses 3V3, but given the maximum current draw of two Si570 devices at 196 mA drove the decision to install a separate 3V3 800 mA regulator on the board.  At my current draw, I might be able to get away with using the Arduino 3V3 rail, but it is pushing things.  Another option might be to replace the regulator but again, I didn't want to modify the Arduino board.

Interestingly, the Arduino documentation says not to draw more than 50 mA from the 3V3 rail which makes me suspect that they may have trimmed the heat sink tab on the part.

I am seeing 13.5 dBm with no attenuation out of the Si570 devices so there is plenty of drive available to allow experimentation with different mixers.  The PI pad resistors can be populated to set any level desired.

I have Wayne, NB6M's Minima build at my disposal for a few weeks to be able to try out the new shield for both VFO and BFO signal sources and am looking forward to seeing how this works out in a practical sense.

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