Bad policy of ignoring level shifters

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jremington
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Bad policy of ignoring level shifters

Post by jremington » Sun Dec 13, 2015 10:41 am

In several SparkFun tutorials and other offerings, I've run across a very bad policy: recommending that 5V electronics be connected to 3.3V (or other) electronics without level shifters. Here is one example: https://www.sparkfun.com/tutorials/240

The author of the tutorial even admits the problem, but is unrepentant:
zagGrad / about 5 years ago / 3

I actually used a 5V Arduino in the example. Though this is ‘bad engineering’ it works fine. In the long run it may end up damaging the pins on the ADXL345, but I’ve yet to have this happen to me. If you’re nervous about using 5V signals to communicate with a 3.3V device you can certainly use the logic level shifter board to interface the two boards.
This leads to a lot of frustration on the part of beginners, as it tends to destroy parts, and is puzzling because SparkFun sells level shifters. Or would SparkFun rather sell replacement ADXL345s than level shifters?

In a second example, the instructions for using the 3.3V OpenLog recommend connecting RX on the OpenLog to TX on a 5V Arduino.
You can also use jumper wires to connect the OpenLog to your system. The minimum required pins are VCC (3.3V to 12V), GND, and RXI (3.3V or 5V).
This is an incredibly irresponsible suggestion. At the very least, one should include a series resistor (e.g. 4.7K) in the TX-RX connection to limit the current from a 5V output.

Why not be responsible to innocent customers, and do the right thing? Please promote "good engineering" instead of "bad engineering".

TS-Tim
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Re: Bad policy of ignoring level shifters

Post by TS-Tim » Mon Dec 14, 2015 10:44 am

Hi,
You make a good point here. You're finding some older tutorials that do in fact support or at least not deny some more questionable engineering decisions. In our past, we have done things with a bit more relaxed mindset of what's necessary versus what's best practice. I would hope that you will notice that our more recent tutorials and hookup guides take a better approach to handling and best practices.

jremington
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Re: Bad policy of ignoring level shifters

Post by jremington » Mon Dec 14, 2015 11:27 am

Thanks. Can you correct the older tutorials?

I ask because I'm responding to a customer who just recently reported damaging his/her ADXL345, following the instructions in the first link I posted.

TS-Tim
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Re: Bad policy of ignoring level shifters

Post by TS-Tim » Mon Dec 14, 2015 12:07 pm

I can certainly request that information be reviewed and revised. :)

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