[Guide] Serial USART/UART 1.8v to 5V TTL level converter

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saliamis
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[Guide] Serial USART/UART 1.8v to 5V TTL level converter

Unread post by saliamis » Mon May 05, 2014 7:54 am

Hi all,

I wanted to interface ODROID U2 via USART/serial via ordinary USB 2 TTL USART module (image below).
The problem with it is that TTL module levels are 5V, while ODroid serial levels are 1.8V.
One can use/buy the USB serial cable from Hardkernel shop. However I wanted also to interface ODroid with a microcontroller using +5V TTL levels - so a USB cable is not an option, a proper converter is required.
20120915_123218.jpg
After doing some research I have managed to build a working, tiny & more optimized solution!
So if anyone needs to built similar converter - here's the Eagle project.

Details:
The schematics are based on a combination of some posts [1] and [2] on from the internet (credits to the authors).
The problem with the [1] is that the 1.8V level is too low & will not open a generic NPN transistor properly/fully, so an inverted schematic must be used as in [2] and only one transistor is needed in this situation.
[1] http://forum.arduino.cc/index.php?topic=160716.0
[2] http://electronics.stackexchange.com/qu ... ransistors

Parts:
The transistor used can be any generic/popular NPN type such as 2N2222/2N3904 or BC546 etc. All parts are absolutely necessary.
The TX 18K & 10K are just a simple voltage divider - if you have other resistor values, then stay at least close to their ration 1.8:1.

Schematics:
schematic+board.png
Pictures of working POC below:
poc.jpg

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odroid
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Re: [Guide] Serial USART/UART 1.8v to 5V TTL level converter

Unread post by odroid » Tue May 06, 2014 8:52 am

Very simple and nice level-up-shifter and level-down-shifter.
Useful example for electronics beginner too.
Thank you for sharing. ;)

g.gregory
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Re: [Guide] Serial USART/UART 1.8v to 5V TTL level converter

Unread post by g.gregory » Thu Jul 24, 2014 12:29 pm

Nice simple example!
I need to make a similar shifter for Odroid (1.8V) <> Pixhawk Autopilot (3.3V)
For the Pixhawk (Tx) -> Odroid (Rx) i can change the voltage divider to get the correct 3.3V -> 1.8V, but for the Odroid (Tx) -> Pixhawk (Rx) would I need to change the resistor values?
Thanks

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odroid
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Re: [Guide] Serial USART/UART 1.8v to 5V TTL level converter

Unread post by odroid » Thu Jul 24, 2014 3:52 pm

"1.8V to 3.3V" needs a level shifter. The level shifter can be implemented with a NPN-TR as described in above schematics.

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Re: [Guide] Serial USART/UART 1.8v to 5V TTL level converter

Unread post by Digimaster » Thu Jul 24, 2014 4:54 pm

Some improvements can be done.
Looks like R2 R3 ratio is for 3,3V TTL.
For 5V TTL it is better 10K and 3,6K respectively.
Smaller values are better for more noise resistance.
In case of long wiring probably small capacitors can be used to prevent front peaks.

TheBigB
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Re: [Guide] Serial USART/UART 1.8v to 5V TTL level converter

Unread post by TheBigB » Sun Jan 18, 2015 4:46 am

D'oh, I only seem to find these guides after the fact...

I had an Arduino lying around, but the same concept applies. This is my setup: https://imgur.com/a/BOF3N

uzsito
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Re: [Guide] Serial USART/UART 1.8v to 5V TTL level converter

Unread post by uzsito » Wed Sep 19, 2018 5:47 am

saliamis wrote:Hi all,
20120915_123218.jpg
After doing some research I have managed to build a working, tiny & more optimized solution!
So if anyone needs to built similar converter - here's the Eagle project.

Parts:
The transistor used can be any generic/popular NPN type such as 2N2222/2N3904 or BC546 etc. All parts are absolutely necessary.
The TX 18K & 10K are just a simple voltage divider - if you have other resistor values, then stay at least close to their ration 1.8:1.

Schematics:
schematic+board.png
Hi, I'm not sure people can build this based on the schematics, because on your drawing you connected TX to TX, and RX to RX...
Serial connection requires these lines to be twisted, if I'm right. People can figure it out of course, but for absolute beginners it can be misleading.

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