Logic Level Shifter problem

Other Hardware General Electronics
21

What is the part number of your optocoupler?
There are optos out there that only need 1.6V, so a current limit resistor on the input will drive the input LED.
Look at the datasheet.

In this case you only need one way shift.
So if you really want to shift from 3V3 to 5V, you could just use a transistor, BJT or MOSFET.
Even going form 24V to 3v3 or 5V an OptoCoupler will do the trick.

In your case going from industrial 24V to microcontroller 3V3, use OptoCouplers, just look them up.

Thanks.. Tom.. :smiley: :+1: :coffee: :australia:
PS. Are you over thinking the situation?

22

Thankyou for your explanation. I can see why it wouldnt work with the optocoupler. Ill see how I will solve that problem later.

As for the LLC-test:
The left and right groundrails are connected, and there is no gaps in the rails on my board. Powering the power-rails with an Arduino Uno. 3.3v on the right rail and 5v to the left rail.

Measured and tested that.

LLC_setup
LLC_setup658×846 179 KB

I just tried to ground HV1 and HV2 as you explained in the picture. I still have 3.3v out from LV1 and LV2. Maybe hard to see in the picture but I include it just to make an understanding on how I am connected.

Edit:
A closeup of the circuit.

LLC_setup_closeup
LLC_setup_closeup932×1200 134 KB

23

Either that board is bad or one of the ground connecions isn't actually connected.
Sometimes the pins on those little boards are too short to make good contact with a breadboard.
Try touchong a ground wire directly to the top of the pin on the board itself

1 Like
24

I have double checked and tested all connections. Everything seems fine. I have also tested with 3 different boards with same results. Maybe a bad batch? I am quite puzzled...

25

So am I

26

One thing I have noticed is that all the logic level shifters I see on Amazon and Aliexpress have the 10K pull-up resistors on either side of the board whereas your board has them all on one side.

I wonder if that is actually a logic level shifter.
A batch of fake boards.

1 Like
27

Could be. It is not like it is the most expensive board in the world. :wink: I know there is a lot of fakes out there.

28

The solder on LV1 is a blob and LV2 looks like a void (nothing there).

image
image921×617 84.9 KB

L/HV3,4 look better. What's their story? (Just do one at a time.)

29

Hard to see. Tried to make a closeup, but I dont know really what to look for. :wink:

LLC_microscope
LLC_microscope1920×1440 314 KB

I'll just accept that this cheap amazon-LLC doesnt work the way I thought, or want... :slight_smile:

30

It does, picture for explanation.
image
Resistors in blue box go to the top row of pads.
MOSFETs in blue box turn 90 degrees.
Then all will resemble the amazon picture(and hopefully work)! :smile:

Some joker built this on a budget leading to no silkscreen markings for where components go, then did some guess work to the layout! :crazy_face: :rofl:

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31

It's a fake!
Don't waste your time.

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32

Still, no harm done in the experiment they were cheap.....
Would only take me 5 minutes(if that) to do. :wink: :upside_down_face:

33

Compare it to this one(try to imagine everything in it's correct position) what else is wrong?
image

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34

If you don't want them sell them to me and I'll fix them. :wink:

35

Hehe. Is it really worth it? :slight_smile: They cost $8 for 10 pcs. You can get them for free, but the postage will be more expensive than that. :wink:

Thanks for everyones help anyway! This is internet at its best. :sunglasses:

36

I would try just one but anyway.
"Curiosity killed the cat" they say. :wink:

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37

Just wanted to say thank you for all inputs on my problem. The boards were totally faulty like @theeccentricgenius pointed out. :wink: Now I received new ones and they work exactly like expected.

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38

Faulty or not level translators?

39

The circuits were soldered on the wrong places on the PCB. Cheap China stuff. :wink:

40

So the boards you now have were made in the US?