1.8v UART TTL to USB DIY for around $5 for CE Boards

General
#1

Most solutions I have seen for a 1.8v uart are pretty expensive, especially if you include the import duty in many countries.
For example to get the official 96boards uart adaptor which costs $14, I need to pay $30 to get it shipped to India. And other solutions like the official usb to ttl module by ftdi still cost alot and other chips based on CPxxxx do not provide the reliability of an ftdi chipset.
So here is my solution using a ftdi based module rated for 5v and 3.3v that costs around $3-$4 and a 1117 1.8v LDO which I was able to get locally for just about $1 for a pack of 5, but is easily available for less than $1/pc

http://www.mouser.com/ProductDetail/STMicroelectronics/LD1117S18TR/

The procedure is simple,

  1. connect the 5v pad on the module to pin 3 of the LDO
  2. Connect pin 1 of the LDO to GND
  3. Connect pi2 to the VCCIO or the Center pin on the Voltage select pins on the FTDI module

And you should be good to go, connect tx, rx and gnd to the 96boards CE.

For a bit more comprehensive explanation:

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#2

It’s possible to cost down this solution :smiley: I used a voltage divider (220 + 200) from the 3.3V pin to GND. The divider makes about 1.73V but this is good enough! Here’s a picture of it attached my Dragonboard.

IMG_7123
IMG_71233264×2448 1.52 MB

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#3

It’s possible to cost down this solution :smiley: I used a voltage divider
(220 + 200) from the 3.3V pin to GND. The divider makes about 1.73V
but this is good enough!

Neat hack. Which boards is it known to work with?

I’m interested simply although its certainly electrically safe the logic
level for RX will be indeterminate. It’s a technicality and very
unlikely to matter in most cases but I’m still curious.

#4

This board was purchased from eBay. I’m guessing any FTD232 (real or fake) with VCCIO pin broken out will work.

#5

Sorry I was clearly a bit hard of thinking this morning… I’d thought the voltage divider was on the TX rather Vref pins.

I take back all the nonsense above about indeterminate logic levels :wink:

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