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level shifter boards not working correctly

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I got 2 DigiX level shifting boards for use with an Arduino Due and they seem to not work correctly.

I have tried writing pins 2-13 low and high by digitialWrite and the pin voltage is nearly constant around 1.9-2.1V for each pin measured by a voltmeter, except for a few which will occasionally read 4.45V when high once or twice.  This is about the same when using a 10k pull down resistor.

As INPUTs, when the shield is disconnected from the board I find the shield outputs ~1.9V to the Due as a digital HIGH signal when the shield 5V pin input is ~> 2.7V, which seems correct, except sometimes they output 3.2V to the Due instead.  Also the Due-side signal is near zero then the input is ground which is also correct.

I tried ramping analogWrite min to max and with the shield installed the output voltage of the 5V pins varies from ~1.9V to 2.3V on some pins and 0-1.9V on other pins.  I verified the Due pins are outputting correctly, but the shield is not.

The behavior is similar on both shields.  Can you please help me resolve this?


Hopefully exeng or someone else with the shield who has had a bit experience with it has something to say on this... as I can't work out what an earth is going on either. I tried pins 5,6,7 with a 2 second on/off and I got a more sensible ~4.5v from those pins (at times... there was a few times there it kept giving me 1.8v and 2.2v :-/ )... but I can't get anything consistent from the top five... I had better luck when running from a USB power bank to ensure the DigiX was getting a proper 5v supply, but I don't know if that related to the problem... the TXB0108 which this is based on should be fine all the way down the 1.2v...  I know from the datasheet this thing is supposed to be auto-direction sensing... but shouldn't 3.3v on the low voltage side be telling it that it should be stepping up to the 'high voltage side' ???

Edit: Just adding that this is no coincidence... I had another level shifter that was still in it's packaging from the kickstarter, and it's exhibiting the same behaviour... I stuck it on the o-scope and instead of a nice sharp 3.3v up and down, it is just quivering around 2-3v.

Pete, perigalacticon,

Sorry, the only level shifting boards I have are for the Oak, not the DigiX.

The TXB0108 used on the level shifter requires a load to produce a proper voltage - so if you put an LED, connect it to another IC, etc on a pin it should be correct and work right - but just a voltmeter will be misleading.

Ah ha... Thanks for that Erik... I'd tried a 10k -ish resistor to GND as a pulldown at one point, but didn't put a load across it... that would would explain the bizarre readings ;)


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