The Weather Wizzard III - for APRS?



I like this station. The old  Davis 7425 Weather Wizard III still keeps on going.   It hangs on the wall in the family room,  displaying the local weather info.

The two projects I always wanted to do with this station is to 1) add a rain gauge, and 2) build a "self-contained" APRS station.  I got my station in 2003 on sale at Fry's Electronics- but even though this little station has been discontinued and is no longer available form Davis, but you can still find it on line.

RAIN!

It has always irritated me the standard 7425 does not come with a rain gauge...  The easy solution to problem  #1 is just buying:

Davis Instruments 7852 Rain Gauge for Davis Weather Wizard & Weather Monitor Stations:

Is it the only solution?

The add on cost is $60 ~ $70 USD.  Since I got my 7425 on sale for $89, it seems a bit odd ~ to my sensibilities anyway ~ that adding this sensor is a significant fraction of the cost of the whole setup.  I think I found a way to get this sensor for 1/2 the cost!

Recently, we re-painted the house and one of my pet peeves is painting cables (don't ask - it's an OCD  thing I think is what  they call it) so I disconnected the sensors to paint.  The Junction box is in a patio area and a pass through hole terminates in a surface mount Wire Mold J-BOX inside makes a nice weather- and mouse-sealed  pass thru for the cable.  ...oh yeah, and wife approved as a family room accessory!

When re-installing the cable thru the hole the RJ-11 plug got hung up in the insulation and became damaged as I fished it through.  The Wind Direction ceased to work on the display. This prompted me into a little investigation...So what mysterious protocol gets the sensor data to the station?   What no serial data to hack? No, they are very simple: analog!

Specifications

Rain Sensor General

Sensor Type . . . . . . . . . . . . . . . . . . . . . . . . . . Tipping bucket with magnetic reed switch

Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Contact closure

Attached Cable Length . . . . . . . . . . . . . . . . . . 40’ (12 m)

Cable Type . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-conductor, 26 AWG

Connector . . . . . . . . . . . . . . . . . . . . . . . . . . . .Modular connector (RJ-11)

Resolution . . . . . . . . . . . . . . . . . . . . . . . 0.01” (0.2 mm)

Input/Output Connections

Black & Red . . . . . . . . . . . . . . . . . . . . . . . . . .Switch terminal

Green & Yellow . . . . . . . . . . . . . . . . . . . . . . . .Switch terminal

Temperature Sensor General

Sensor Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Platinum wire thermistor

Time Constant

In Still Air . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 240 seconds

In Liquid. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 seconds

Attached Cable Length . . . . . . . . . . . . . . . . . . . . . . . . . . 25' (7.6 m)

Note: There is no absolute maximum cable length. Increasing the cable length above 300' (90 m) causes an increased measurement error at

a rate of approximately +0.06°F (+0.03°C) per 100' (30 m) at 136°F (60°C) and +0.012°F (+0.006°C) per 100' (30 m) at 77°F (25°C).

Cable Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-conductor, 26 AWG

Connector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Modular connector (RJ-11)

Input/Output Connections

Black & Red . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Common

Green & Yellow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Temperature (variable resistance to common); 10KOhm, nominal

Wind Sensor General

Sensor Type

Wind Speed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Wind cups and magnetic switch

Wind Direction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Wind vane and potentiometer

Attached Cable Length . . . . . . . . . . . . . . . . . . . . . . . . . . 40' (12 m)

Note: On Monitor and Wizard stations, cable lengths longer than 140' (42 m) between sensors and console may artificially limit wind speed readings. That

is, beyond that length, maximum recordable wind speed decreases as cable length increases. For example, with a length of 140' (42 m), the maximum

recordable speed exceeds 175 mph. At 240' (72 m), however, the maximum recordable speed drops to less than 140 mph. Below that upper

limit, however, the anemometer's accuracy is not affected.

Cable Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-conductor, 26 AWG

Connector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Modular connector (RJ-11)
Input/Output Connections
Black. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Wind speed contact closure to ground
Green . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Wind direction pot wiper (360° = 20 kOhm)
Yellow. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pot supply voltage
Red . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ground

Based on these specs form Davis I came up with the following schematics:

So what about that rain sensor?  It is just a reed switch and magnet. There are plenty of tipping bucket sensors on the market for less than $70! that use these. For example:

16095  Acu-Rite 00899 Wireless Rain Gauge
Price: $34.99

http://www.klockit.com/products/dept-64__sku-16095.html

OK, so it's not the best one we ever saw.  Typically, the made in China electronics in these types of products will likely fail and stop working in most of these after a month or so - and the plastic is probably not UV stabilized like the Davis 7852 so it may not be the best for harsh environments but  it is readily available and - oh yeah, I have a broken one!

I got mine from the Home Depot to measure the irrigation sprinkler watering on my newly sodded lawn.   It has a reed switch and magnet...which attaches to a transmitter (you know...the part that no longer works).  I think the main failure mode of these is the soldering of the circuits, not the switch and magnet assembly. I think the soldering is done by hand and I am sure not much time is allowed for the assemblers for each unit...

This is an easy hack!  Disassemble, Rip out the transmitter, get an RJ-11 cable, solder the RED & BLACK wires to one side of the reed switch and the GREEN & YELLOW wires to the other side (or what ever colors you have), re-assemble, and ..done! 

...Except for calibration. The interesting thing is the specs say 0.02" resolution but the buckets look the same as the Davis' buckets. It may be the display waits for two tips to register a count or the buckets take a little bigger drop to tip.  This Acu-Rite model happens to come with calibration screws and a method to calibrate...so making it match the 7425 should not be an issue, in fact we can easily re-scale in the count in my APRS_WX modem firmware as well if needed even if we can't fix value displayed.

BTW-- They no longer carry it in Home Depot, I found these specs for mine online in a clockmaker's catalog.  Does the successor's sensor look strangely familiar? Yes, it looks exactly like the $99 sensor hummmm maybe I ought to check it out?

...and from the comments it too stops working after a few months!

The Weather Channel Wireless Rain Gauge

Price: $24.99

Model # WS-9005TWC-IT 

Internet # 100599154

Ships FREE with $45.00 Order

Strangely, This item cannot be shipped to the following state(s): AK,HI

http://www.homedepot.com/buy/outdoors/outdoor-living/the-weather-channel/wireless-rain-gauge-6153.html

APRS!

The major problem with #2 is getting the weather data out of the console.  The unit does send data serially but, again it has a cost. ( no, I am not cheap, really.)  The only way I saw to do this for years was to add the Davis Weatherlink For Windows 7862 software package (~$150) which comes with a little interface device called the "Data Logger"  So... since I don't want a PC in the loop the software would be useless to me anyway in my APRS setup. 

Well, useless after the command protocol was hacked ~ but that would be simple matter with a seral data analyzer snooping at the comm port on the PC as it interfaced with thier software. But as it happens, the command protocol that was not readily availble is now ~ Davis has released their SDK for Weatherlink! ☻ 
Because of this released Davis documentation, and some intrepid hackers ( thanks, DeKay )

http://madscientistlabs.blogspot.com/2011/01/davis-weatherlink-software-not-required.html

It has been also shown that this device is little more than a RS-232 level converter!  The keyword is; convert - you don't want the full ±12 Volts going to the weather station.  This APRS modem I designed a while back should be able to be easily modified to interface with this directly. The GPS dongle should still work normally as well.

This PCB  was developed from these schematics a few years back, what I did was take an existing design, modified slightly and made a PCB.  In fact,  I am currently using two of these boards in my APRS stations.  It works great and is very compact.  ...and I own the source code!  Yes, I will post it.

The two connectors on the right are on a snap off option board I made when I fabricated this PCB to allow the GPS info to get tapped into, so I could add a remote GPS display. It was free due to the small size of the TNC board ( 2" x 3") and it provides a sturdy interface to the GPS device. ( OK ~ maybe let's just say I am frugal?)

As you can see from the schematic, it has a built in level converters for RS232 so we have access to both the ±12V and +5V sides.  ( Note: This circuit can also run @ 3V)  This circuit board also contains all the components and software for a complete self-contained APRS modem. 

I may revise the board at some point to allow for an internal temperature and battery voltage (for telemetry) as well as barometric pressure, and relative humidity sensor interfaces on-board to fill in the missing WX data.  I also will probably change to a better connector vs. the audio jacks I originally used. BUT - I still have two of these boards waiting to get built!

All we have to do is modify the FIRMWARE to give the correct commands, add a couple of jumpers and connector for low-voltage serial data (the RJ9 4-pin connector which interfaces to the 7425 seems common but finding one that fits and has all 4 conductors is a bit of an issue as I found out), then receive the raw WX data from the station, format the WX data unto APRS packets, and shazam! APRS-Wx packets start flying!  More to follow on this project as well...STAY TUNED!

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