Problem with TXS0108E Logic Level converter

[psychoboss]

Hi together
I trie to use a ST7735 Display with my Arduino UNO. I bought a TXS0108E Logic Level Converter to reach the 3.3 volts. I wired everything up like in the tutorial and it did not work. So i hooked up the converter to my oscilloscope and the Arduino. I sent PWM signals with the Arduino. The oscilloscope showed me the PWM signal only on the high voltage side. There was no output at the low voltage side all the time. I tried it on another TXS0108E converter and it did not work too. Does anybody know how to fix this?

PS: Sorry for my english.

Greetings Tim

[6v6gt]

You've understood that the logic level converter needs 2 power sources to work?
 In your case, a 5.0v and a 3.3v supply with a common ground. It does not act as a voltage regulator.

Edit:
Clarification of an apparently  ambiguous sentence structure.

[psychoboss]

Yes i connected 3,3 Volt 5 Volt and ground

[dlloyd]

Is OE connected to 3.3V? (or driven high)

[TomGeorge]

Hi,
Welcome to the forum.

Please read the post at the start of any forum , entitled "How to use this Forum".
OR
http://forum.arduino.cc/index.php/topic,148850.0.html.

Can you please post a copy of your circuit, in CAD or a picture of a hand drawn circuit in jpg, png?

Thanks.. Tom..

[psychoboss]

Hi tegether. I drawd a picture with paint.

[dlloyd]

I think you need to ensure that the outputs are off (high impedance) during powerup.
If so, something like this could work (turn on OE in setup) ...

EDIT: See reply#8

[TomGeorge]

Hi,
OE at the actual chip is OE Bar.
The PCB does not show any logic inversion, so try connecting OE to gnd.

Tom...

[dlloyd]

Hmm...Here it says:
When the output-enable (OE) input is low, all outputs are placed in the high-impedance (Hi-Z) state.
This'll automatically happen (1K pulldown) during powerup.
Maybe there's a similar part with active-low OE or am I referring to different part than the OP is using?

EDIT:
Just realized ... the UNO has a 3.3V pin, so OE could be directly connected to this (similar to shown in datasheet). In this case, use the 1K as a pulldown from OE to GND.

[6v6gt]

This describes similar issues:
https://forum.arduino.cc/index.php?topic=406261.0

Can you try the blink sketch (or similar where the Arduino pin is defined as an output pin) and see if that gets through to the 'A' side of the device?

[psychoboss]

Hi together.
I tried connecting the OE pin to Ground and 3,3 volts. It did not work in both cases. The Signal did'nt come trough even with slow changing like the blink sketch or continuus volatge.

[dlloyd]

Uhm... OE needs to be tied to 3.3V then also connect a pulldown resistor (i.e.1K) from OE to GND. (see datasheet).

This is a touchy part to get the signal to pass through ... may need a certain load on the output (5V side) to get it to work. Do a search on this forum and elsewhere for more info.

[psychoboss]

I tried both, it didn't work. I also connected the Display and startet the exmple sketch. There was also no Signal on side B.

[6v6gt]

I tried both, it didn't work. I also connected the Display and startet the exmple sketch. There was also no Signal on side B.

Do you mean the sketch was running connected to side B, the high voltage side, setting  pins etc. , and nothing was measurable on the low voltage side, side A ? That is what your earlier diagram implies.

[dlloyd]

I tried both, it didn't work.

So you tried this?