Sandaysoft

I'm having problems with my Ambient WS-2080. It keeps losing contact with the sensor array. I'm tired of hoping it works each day, so I want to send it back and build my own solution. I have plenty of coding experience, and while I don't really like fiddling with electronics and I/O lines, I'll do it if I think I can get a good solution.

What I want to build is an outdoor weather sensor that measures temp, humidity, rain, wind speed and wind direction. UV or sunlight measurement would be nice. I want the sensor to be a wifi node on my home network, transmitting a TCP stream. I happen to have AC power available where I want the sensor to be, so wifi is feasible.

My current thinking is a Raspberry Pi for the processor, because it's cheap and I can plug a USB wifi device into it, and (probably?) use the small set of GPIO pins on it to gather data from the sensors.

That leaves the problem of: where can I buy (inexpensive) sensors, and what electrical interface do they provide? In a perfect world, someone would make a sensor array with a USB interface, but I doubt that exists. Can folk make recommendations, and/or warn me off this approach because they know it's failure prone?

If the total price exceeds a Davis weather station with USB interface, the project has failed. That said, I'm willing to spend money and time on a solution that's going to be rock solid. Advice very much appreciated.

Can't you get closer to the sensor array with your base station then? Or does it still loose contact when they are next to each other.


The reason why it probably doesn't exist is that running a long distance USB cable is mostly not a good idea. Over longer distances (and outdoors) network cable (cat 5) is better idea. It's why 1-wire devices work with network cable.

Hi Scott,

I'm not sure that the RaspberryPie has much in the way of "I/O pins" and availablity is certainly an issue at the moment. I think perhaps you should be looking at the Arduino system. Personally, I'm looking at the alternative PICaxe system because I want something (wireless) to run continuously off a couple of AA cells.

I believe that both support the "one wire" (a misnomer) bus/protocol for which many types of sensor are available. I don't have any experience of these devices myself, but some on this forum certainly do.

Cheers, Alan.

Oooh. I found an adapter for 1 wire protocol -> USB:
http://www.hobby-boards.com/store/produ ... aptor.html
and a variety of 1-wire devices at the same site. This raises the prospect of being able to get sensor data to any tiny microcomputer with a USB port, and not having to fiddle with I/O pins on a board.

The components are overpriced, but looking at the photos, it appears my ambient weather station is using some of them - so maybe all the sensors I already have are one wire devices and I don't have to buy many sensors.

Anyone looking at Arduino or similar boards might also consider Nanode http://nanode.eu/ - an Arduino compatible board with RF and Ethernet connectivity.

(I know nothing about either, but keep thinking it would be an interesting thing to play with if I didn't have so many other things I ought to be doing.)

_________________
Jim

Probably too simple:
Did you try to rotate the transmittor vertically, about 90 degrees? From what I have read, this could improve (or worsen) reception.

_________________
http://members.upc.nl/h.graaf507/weer/index.htm

It comes with a 26 pin header that provides GPIO (at least 8, as I recall), SPI, I2C, and UART, so there's quite a lot of connectivity. From the datasheet, it's also possible to configure interrupts on the pins, but not sure how these translate to user space code.

It's also just passed CE/FCC/etc. testing, which was the hold-up preventing the distributors shipping, so I suspect ten thousand people will soon have real devices to play around with.

The downside is the power requirement, since it will never reach microcontroller levels - it needs stable 5v to drive USB devices, and even with nothing connected will consume a watt or two. Less of an issue in the garden, since an old car or bike battery with a solar trickle charger should keep it running.

I'll try twisting the transmitter. That's at least a cheap solution. If it helps, fie on Ambient support for not suggesting it.

But I'm considering just sending it all back and building from scratch. I'm contemplating this because there's a couple of unusual characteristics about my intended use:
1. I happen to have AC power near where the weather station, and I'd rather use that than battery power. I just want to avoid the yearly fuss of pulling the station down to replace batteries; and if my power's out I'm ok with losing weather data.
2. I want wifi transmission of data, using TCP. I've had no problem with wifi around my home, and using corner reflectors to boost range is something I've had success with. I want TCP because it takes care of retrying failed transmissions and because I'm familiar with programming for it.
3. Programming anything in any language doesn't scare me, but I'm a danger to myself and others with a soldering iron. I need to stick to breadboarding and screw terminals on the hardware side. I'm a software guy with a natural loathing for hardware.
4. I don't need or want a fancy display unit. I want the data on a computer, where it feeds displays I already have.

My current thinking is to get sensors from Hobby Boards - these are all one-wire interfaces, and my limited experience with one-wire has been positive. An arduino is my current plan for processing, because it handles C++ and because it is said to be good for one-wire. I hope to find a wifi unit for it with an actual external antenna, because being able to orient antennas and use corner reflectors on them is a path to success and joy.

My alternate plan is to keep the sensors from my current Ambient (which means I don't get my $114 refund), and hook them up to counters and A/D devices that speak one-wire, that Hobby Boards also sells. This is slightly cheaper and means I don't need to fuss with designing new mounts for the sensors. But it means more wiring fuss, and more fear and loathing over getting electrical interfaces to work.

Anyone see problems? Any experiences with Hobby Boards? Am I just begging for trouble?

If you are stuck on using WIFI, then the one wire stuff does not make much sense. With few exceptions, the sensors are standard analog devices, digitized and then transmitted by one wire. If you are planning a processor to collect data and manage a WIFI ink, then you might as well use it to interface to the sensors and save yourself a complete layer of cost and translations.

If someone wants to post a complete analog design involving an arduino, and if I don't have to cut any circuit boards or do much soldering (I *love* screw terminals), then I'm all ears. It's just that at my stage of life, "easy and fast" can sometimes trump "cheap and time-consuming". And one wire interfaces, while they add expense, mean the wiring is a matter of minutes and the coding not much slower.

Hi Scott

I've just spent 3 months developing a station that will accept data from a number of sensors, including one wire, and then display that data in Cumulus. This is based on a microcontroller to gather the data, process it into usable form, then present it by the USB interface to Cumulus. It probably has a couple weeks effort yet before it's ready for prime time, mostly because I received a bad one wire device and I'm waiting for a replacement. There is curently no wireless link, although the architecture allows for adding one in future if I ever think it's worth the effort. It does have onboard sensors for the indoor measurements, and a built in data logger the same size as the Fine Offset. It has been happily displaying data in Cumulus for a couple weeks now.

I started the project after my own Fine Offset frustrations, and with discussion and support from "41South". If fast and easy is what you are looking for, then rather than trying to build your own, send me a private message and we can discuss getting a copy of it constructed for you.

I can tell you that I wouldn't want a weather station I can't use with Cumulus, and it's unlikely Steve will ever support home made stations unless they use an existing interface. I can also tell you the project was non-trivial with plenty of surprises.

Final point, re my original comment: one wire only brings transport layer to the table - you still need to code for all the sensors. If you use WIFI for the transport layer, then what does one wire add?

I like one-wire because I can add and drop sensors with minimal wiring, without touching more processor pins. (I'm prone to frying whatever I touch, so I want to touch very little.) It's purely convenience; I want to get two pins working and be done with messing with the processor forever after, except throwing code on it.

Alright, so... having priced one wire components for everything, I think I'm giving up and moving away from one-wire for windspeed, rainfall, and wind direction. Windspeed and rainfall are just digital pulses, which the processor I have (netburner 5270) won't have any problem debouncing and counting.

Wind direction looks dicier. It's an array of 8 different resistances, up to around 100k. The cheap way is to use the resistances to charge a cap, and measure the time it takes the cap to get high enough in voltage to look like a logic 1 to the processor. The problem with that approach is that caps drift as the temperature changes... this won't work.

So instead I'm considering using the resistance from the wind wave to control the duty cycle of a 555 timer. Messing with some numbers, I can probably get a measurement in 15ms, worst case. (Wait for the 555 to go high, measure the time high, measure the time low, divide and look up the answer.) Since duty cycle is independent of the capacitor value, it doesn't matter much if the cap value varies with temp.

Has anyone tried this? Is there a better way? The one-wire solution in this case is around $58 - too much.

Hi,

If you're considering the FO wind vane, that's exactly what they do. But they pre-calibrate the capacitance against a known resistance first.

The issue is that the resistances don't run in sequence (and there are actually 16 values because two reeds can operate at the same time) so some form of "lookup table" is required. A small microcontroller is the obvious solution, it's exactly what I'm planning to do (with a PICaxe) in my current project, maybe soon to be revealed in the Homebuilt section.

Cheers, Alan.

>If you're considering the FO wind vane, that's exactly what they do.

I already have the FO weather vane, so I guess I'm using it.

How do they account for cap drift? reed switch debounce? The vane moving in the middle of the measurement? Or do they just hope for the best? Do they use a 0.1uf cap (Which means the worst case read time is probably around 11ms?)

I suppose I'll just remeasure until I get 3 equal values in a row. I was hoping for something better.