Hello guys, my first post, but not first time I'm on this forum
During time I found some valuable information about Davis' v3 interface here, and devised few of my own solutions that I implemented successfuly on 5+ Davis Vantage Vue and Vantage Pro stations that operate 24/7 for years. So let me share that with you.
I read great PDF about Davis v3 protocol (
http://meteo.annoyingdesigns.com/DavisSPI.pdf) by
torkelmj and decided to make v3 emulator presented in that document. So I bought few ATTiny85 chips, already had programmer, and as base board I used interface board by
belfryboy and simplified it. To skip USB->TTL->RS232->TTL conversion I reduced it to USB->TTL, reducing the cost and complexity, while keeping communication in perfect order. Also, since Davis' proprietary software interface costs money, I use Cumulus to stay in free software&hardware domain.
My design uses cheap USB->TTL cable from eBay, it's tested with Windows7 and Windows10 with latest updates and it works fine, it uses Prolific PL2302HX chip, and drivers are available from Prolific site. If it shows exclamation mark in Device Manager just reboot computer and it will work. Also I got info that it works with Raspberry Pi, but didn't tested it myself.
Can be bought here for 1.5 USD (link to specific seller is just for picture reference, you can buy from any seller, there are plenty on eBay offering exactly this same cable) :
https://www.ebay.com/itm/USB-To-RS232-TTL-UART-PL2303HX-Auto-Converter-USB-to-COM-Cable-Adapter-Module/201539573206 My board has three pins that connects to this cable marked with letters on solder mask (G-green, W-white, B-black) for easier connecting.
Boards can be ordered directly from OSHPark or downloaded and made in any PCB factory you like, I designed board and put open-source-hardware mark, feel free to improve it if you like, and hopefully share design with others. If someone wants schematic and board in Eagle format, I can attach them. Just board is here :
https://oshpark.com/shared_projects/M0mczaXCSoftware in ATTiny is compiled from Bascom sources from above mentioned PDF, they are work of user
watson from this forum. I'm attaching HEX files, but important thing is that AVR hex doesn't contain fuse bits information so you will have to specify them while programming chip. They are : Lock : 0xFF, FuseLow : 0xC1, FuseHigh : 0xDF, FuseExtended : 0xFF. It is important to program them correctly, else program won't work. For me both constant and random versions of firmware worked, but to be sure use constant version.
Besides ATTiny85, you will need : 1k or 470R resistor in SMD 0805 format, 0.1uF ceramic capacitor in SMD 1206 format and 3v Zener diode in SMD MINIMELF format. Capacitor is used as bypass cap, actually not needed in this application, but I put it for a good practice. Resistor and Zener are used to clamp 5V from USB->TTL cable to 3V, it worked for me even with 5V, but for a good practice it's better to clamp voltage as microcontroller in Davis operates at 3V. Only remaining part is 2x10 female header with 2mm pitch. Original data logger uses header that is a bit longer than ones I could find, by not pressing it directly to board, but soldering it with 1mm space between header plastic and board will do the trick and header will go firmly into expansion port.
So that's my solution, all for around 10 bucks. Once again, many many thanks to all users from this forum that made this interface possible, especially three mentioned above. Great work guys!
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