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level shifter boards not working correctly

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perigalacticon:
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?

Thanks.

PeterF:
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.

exeng:
Pete, perigalacticon,

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

digistump:
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.

PeterF:
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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