Photos of the insides of Fine Offset sensors.

[Gina]

I thought it would be useful to start a thread showing the insides of the sensors of Fine Offset type weather stations. I'll start this off with the Rain Gauge.

Inside the rain gauge with the cover/funnel removed. The small piece sticking out of the rear of the bucket part contains a magnet which operates a read switch on a circuit board contained in the box at the back. The cable comes out of the bottom and goes through a hole in the wooden board I've screwed the unit onto.

Rain_Gauge.JPG

[Gina]

Wind vane - wind direction. NB the cable to th transmitter unit has broken off.

[Gina]

Transmitter, temperature and humidity outdoor unit.

Left to right - two of the battery connectors, RJ11 sockets for the cables from the wind and rain sensors, temperature measuring thermistor, the little blue "blob" and the humidity sensor is on a small daughter board with 2 surface mount chips. The red LED gives a long flash after connecting the batteries and a short one each time data is transmitted (every 48 seconds).

ws-tx-t-sml.JPG

This is the underneath on the circuit board, showing all the solder connections, surface mount components and the main and transmitter microchips covered by a black compound. The transmitting aerial is a circuit board track around the edge of the blank area to the right of the photo.

ws-tx-u-sml.JPG

This is the version without the radio controlled clock and transmitting on 433MHz. The radio clock version has the clock chip mounted on the circuit pad in the lower middle of the photo, with a small ferrite rod aerial attached to the other side of the board, connected by a pair of wires through one of the holes.

[RCE]

keep up the good work Gina

[Gina]

Thanks Alan

[malc-c]

Gina, these images are very interesting. I wondered what device was used to detect the temperature, and thought that they might be using one of the I2C one wire sensors such as DS18B20... bit disappointing to find out it's just a thremister

[DrMD]

If I can add to Gina`s work, Showing the differences in the tranmitter and adding the consule which is the NC265.

[Gina]

Thank you All contributions to this thread are most welcome. And thank you Steve for making it a sticky

[Gina]

Following from the other sticky thread, here is the circuit diagram together with the resistor values, for the wind vane (wind direction sensor).

SW1 R1 33K
SW2 R2 8K2
SW3 R3 1K
SW4 R4 2K2
SW5 R5 3K9
SW6 R6 16K
SW7 R7 120K
SW8 R8 64K9

Wind_Vane_CCT.png

[Gina]

The way this sensor works is that a magnet attached to the rotating vane turns on one or two of the reed switches. It is meant to detect wind directions between the 8 compass points by relying on the magnet turning on two adjacent reed switches. That is thought to explain the rather weird sequence of resistor values associated with the corresponding switches. The chip in the main transmitter unit converts the resulting resistance into a digital value which is then turned into a number between 0 and 15 in the firmware.

My personal experience (with my own sample) is that this interpolation doesn't work well in practice. At best the ranges of angles for each of the 16 compass points is far from equal and with mine, the reed switch sensitivities vary so much that some points are missed out entirely! This is cheap and cheerful but far from accurate. Not that the vane itself is particularly stable in most winds - a subject much discussed elsewhere in these forums.

Before these PWSs came on the market, I was toying with making my own - I'm a bit of a "closet inventor" A wind vane is not difficult to make - we used to make such things as children. Adding an electrical sensor is a bit more than child's-play. I had planned to use a disc of black and white segments (or holes) and photo-transistors to encode the angle into a digital value. 16 compass points requires 4 bits and I was going to use the Gray Code to avoid more than one bit changing at a time. A Wikipedia page explains the Gray Code quite well http://en.wikipedia.org/wiki/Gray_code

[Gina]

Having recently bought a second FO station kit from Maplins I've noticed a few changes in the design of the rain gauge. These two photos show the differences.

Top view with the covers removed. Two differences - stops for the buckets and maybe some protection against spiders etc. by a grid of 6 small holes below each bucket versus a great gaping hole. I think the problem of wind blowing underneath would be lessened too. (New one at the front.)

new1.JPG

And this shows the underside with the new one at the bottom

new2.JPG

[wd40]

That is interesting on the wind entering the older, large, open drain. I just got mine a couple of weeks ago and it too has the grid like your newer model.

[geoffw]

That is interesting on the wind entering the older, large, open drain. I just got mine a couple of weeks ago and it too has the grid like your newer model.

I must take a look at the replacement I had from Maplin a few months back!

[MartinDn]

Mine was purchased in July, and has the grid.

[firedude52]

Great info! thanks!

Tony
http://morrobayweather.us/