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June 18, 2017
about 2 years ago
@ppelleti, which voltage did you use for your external power supply, 3.3V or 5V?
When powering from 3.3V, I can make it work through the PI's GPIO serial pins.
But, when trying to run it at 5V, I've been unable to get the reader to work with the GPIO serial pins. I'm under the impression that the reader works in such a way that if its supply voltage is 5V, then the serial lines must also run at 5V level. So, when powering it at 5V, I've tried two different bidirectional logic level converters, to try to interface it to the GPIO serial pins. But neither has worked. I'd love to know why....
It works fine if I use USB instead of the GPIO pins. Specifically, I've connected the board's VCC and ground direct to the Pi's 5V and ground, and am only using the TX and RX pins on my FTDI Basic breakout (with the jumper set for 5V).
I'm using that Python binding, and its working well.
I've also tried it at full power. The orientation of the tag makes a big difference. With the SparkFun tags, I've found that read range is best when the long axis of the tag is parallel to the long axis of the reader board. As long as those two axes are parallel, board or tag can rotate around those axes and read range still seems good. But, rotate the tag so that its long axis points directly at the reader, and range drops dramatically.
It also depends how you're holding the tag, if you happen to be holding it in your hand. They don't like being right next to your hand - read range seems to drop.
I also suspect, but haven't proved yet, that power cables near the reader may reduce range, and that the quality (e.g. smoothness) of the supplied power (VSS) matters. E.g. I seem to get nearly 50% more read range when powering it from the +5V on my Raspberry Pi, compared to my other 5V power supply. I haven't investigated much, but I'm guessing it may be that the output power from the Pi has less noise and irregularities.
Has anyone tried the on-board antenna at full power? Like ppelleti below, I'm only seeing about 1 cm of read range with the 5 dBm power that's recommended when USB-powered. On full power, does it really reach the advertised "1 to 2 feet" at 27 dBm?
Could it be your Ardunio's power regulator over heating, as per Power section of the Hookup guide?
The Hookup Guide for this product says to power your Arduino with 5V when using the reader (to reduce heat build up in the Arduino's power regulator). It shows examples of a RedBoard configured this way. However, my Arduino Uno is documented as requiring 6, ideally 7, volts as its minimum input voltage. Apparently if you feed in 5V then the regulator's output is too far below 5V. What's the recommended solution for those of us who want to read at the reader's full power (and so can't power from USB), and who have standard Arduinos?
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