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Topic: How to wire Logic Level Converter ? (Read 5441 times) previous topic - next topic

noname2x

Aug 06, 2016, 10:31 am Last Edit: Aug 06, 2016, 10:45 am by noname2x
Hi everybody, i am really frustrated after many days try to wire the Logic Level Converter. I bought 2 of these pieces https://www.geras-it.de/documents/image/44/441/441.jpg and want to use it with the HC-SR4

I wire exactly like schematic , but it didn't work. So i try to test it with a LED. In the attachment is my test wiring with arduino

red 3.3v to a2 logic input
white 3.3V from Arduino
orange, blue is ground
green output at 5V site
yellow 5V from arduino

The LED glows very weak, the measured voltage is just about 1,0v to 1,5v . The same happens with the second piece , i have no idea why  :smiley-confuse:  . Can somebody help me please ? Thanks so much

Riva

What schematic are you referring to as I don't see one on the product page here.

Have you also connected the OE, VA, VB & GND correctly?
Don't PM me for help as I will ignore it.

noname2x

#2
Aug 06, 2016, 11:07 am Last Edit: Aug 06, 2016, 11:17 am by noname2x
Thanks for reply, the schematic here http://www.artekit.eu/using-logic-level-converters/ .

VA i connected to 3.3 V from arduino, VB to 5V and same Ground for both VA an VB, OE unconnected

TomGeorge

Everything runs on smoke, let the smoke out, it stops running....

TomGeorge

Everything runs on smoke, let the smoke out, it stops running....

TomGeorge

#5
Aug 06, 2016, 11:32 am Last Edit: Aug 06, 2016, 11:36 am by TomGeorge
Hi,
Question1, the BRIGHT Led you have on the protoboard, where is the current limit resistor?
Question2, why do you need a level interface between 5V UNO and 5V HC-SR4?

http://arduinobasics.blogspot.com.au/2012/11/arduinobasics-hc-sr04-ultrasonic-sensor.html

Tom.. :)
Everything runs on smoke, let the smoke out, it stops running....

noname2x

1. the LED can be drove directly from 5V (tested) , i just use it to see if the the chip output correctly
2. I actually use another linux embbeded system which has 3.3v GPIO . The point of using Arduino is to have the 3.3v and 5V output just for testing the chip

outsider

If that LED hasn't melted yet, try it with a 470 - 560 R resistor in series with the LED.

noname2x

But the output is still not correct .... Input is HIGH on 3.3v Site but on the 5V Site there is only 1.5V ?

MorganS

...Which is the forward voltage of the LED. You won't see any higher voltage until the LED pops or you put in an appropriate resistor. Wear eye protection.
"The problem is in the code you didn't post."

noname2x

I have to remind you guys, the problem here is not about the LED ! It has nothing to do with the LED , the LED is just there to check if there is voltage there. Later if everything work correctly , i will use that setup with the Ultrasonic sensor . I am asking why my wiring not work ? and why the output is only 1,5 V at the 5V site althought i do exactly like instruction ? :( :(

avr_fred

#11
Aug 06, 2016, 06:11 pm Last Edit: Aug 06, 2016, 06:14 pm by avr_fred
You are not listening to those that know far more about electronics than you. Yes, it has everything to to do with the LED. You asked why the LED is so dim and why is there only 1.5 volts output. Others have explained why but you have dismissed them without learning anything.

Please do as the others have suggested and place a 470 ohm resistor in series with the LED and then measure the output voltage again on the 5 volt side. You'll see that it has risen to approximately 5 volts and you should see about 3 volts across a white or blue LED. That will prove the logic level convertor is working. That is of course if you've not blown anything up...

Once you've stopped chasing the "red herring" you've created by using the LED improperly, you can get on with troubleshooting the original problem.

noname2x

Ok guys , i am sorry, i am just so frustrated about that problem. So this time i remove the LED , i measure the open voltage at the pin -> 0V . I try to connect pin OE to 3.3v , the output is now at 5 V . I thought it worked ... but not actually . The thing is when i put the pin on 3.3V Domain on LOW , the output on 5V domain still there. Really really confusing ! :(

runaway_pancake

"Who is like unto the beast? who is able to make war with him?"
When all else fails, check your wiring!

Southpark

#14
Aug 07, 2016, 04:00 am Last Edit: Aug 07, 2016, 04:30 am by Southpark
Thanks for reply, the schematic here http://www.artekit.eu/using-logic-level-converters/ .

VA i connected to 3.3 V from arduino, VB to 5V and same Ground for both VA an VB, OE unconnected
First of all. Have you read-up on what each of those pins (eg. 'OE') do? Or what they are?

OE is 'output enable'. All outputs are "enabled" when the pin is at a logic-high voltage. Outputs are disabled when the pin is at a logic-low voltage. So, should probably just connect the OE pin to a logic-high voltage.

In many cases, the manufacturer may have a 'default' voltage level on that pin (via an INTERNAL pullup resistor, or sometimes a pulldown resistor). Hopefully the manufacturer guide indicates it. But yep....there are some times where those idiots don't tell you this, or they don't put that information up-front for everybody to see clearly. But this is often typical of data sheets/user guides/spec sheets - where instead of telling everything as it is (clearly, with useful typical examples), they create cryptic puzzles for users to solve for themselves.

The 'A' side is the lower voltage side. The 'B' side is the higher voltage side.

Now, as for the meaning of 'outputs', I believe that would mean..... if you use say pin B2 as an input, then pin A2 would automatically become an output. And vice versa.

So, apart from seeing what happens if you tie the OE pin to a logic-high voltage, could also try putting an electrolytic capacitor (eg. 100 microFarad) between 5V arduino pin and the arduino GND pin..... which could help to cut down on supply voltage fluctuations (if any).

The same happens with the second piece , i have no idea why
That's because you didn't follow one of the golden rules of electronics..... to check on manufacturer specifications to see if the device is able to output the required amount of 'power' (voltage and current) to drive the device (ie. to drive the LED). In many cases, if this isn't checked in advance, then it can lead to undesirable results.... like damaged components, things not working, etc.




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