Topic: HOW TO: Run more than one Vantage Pro 2 wired console

[SLOweather]

I checked this with Davis Tech Support and they agreed that it would work. Today, I proved it. (Not even most Davis dealers know about this...)

Before the VP2, we had a WMII in the living room and a remote display in the headboard of the master bedroom. I wanted to do the same thing with Vantage Pro 2s.


Background

The flat phone cable between the VP2 console and the ISS has 4 wires in it. The outside 2 carry nominal 5 volts from the console to power the ISS. The inner 2 are the data. The protocol is serial RS-485. Unlike RS-232, this balanced line can be extended farther, which is why the ISS can be so far from the console. It is also inherently multi-drop, meaning that there can be units connected in the middle as well as at the ends.  

There is one requirement for multi-dropping on a network like this. It has to be an electrical daisy chain (not a star) with the data pair running continuously from one end to the other. Long stubs or a star configuration can cause echoes or ringing and scramble the data.

The Gotcha

One thing Davis did caution me about was to ensure that I was using one console to power the ISS. This means that only the data pair are connected between the main and remote console(s).

How I did it.

My ISS cable runs from the ISS underground to the garage and from there to what my wife calls The Brain Room (BR), where it's punched down and jumpered to the CAT5 cable that runs to the console in the living room. Since the ISS requires only 2 of the 4 pair in the CAT5, I spliced one of the spare pairs at the jack to run the data back to the Brain Room over the same CAT5 cable.

In the BR, I punched down and jumpered that pair to a pair on the CAT5 that runs to the master bed room, which I used in the past for the WMII Remote Display. In the headboard, I connected that pair to a phone jack, and plugged the new VP2 console into it.

Note that the 2 consoles don't communicate with each other at all, so the new one will need to be configured manually (time, lat, lon, elevation, etc).

And if you really needed to, you could even install a WeatherLink in the remote console. In that way, you could even run 2 WeatherLinks, if you had a need to.

I don't know what Davis says is the max limits for distance or number of consoles on their network. I think the RS-485 spec says 4000' and 256 units.

(And I realize that wireless VP2s will do this as well. This isn't intended to be a referendum on the merits of wired vs wireless. Each has its own merits, and for various reasons I chose wired.)

[tweatherman1]

Wow,
SLOweather can you show any pics of how you did it. I currently have three weathermoniter II's and one vantage pro 2 wireless and thinking about adding some more in the future.

Thanks,
Tim

[SLOweather]

Sorry I somehow missed your post Tim.

Let me think for a bit about what pics I could post that would actually be meaningful, and not just look like a jumble of wires...

[dalecoy]

OK, thanks to this thread I now have two consoles receiving data from my VP2 wired system.  Seems to work fine - of course, after I got the history and calibrations (baro, temp, etc.) set correctly on the second console.

I've noticed that the two consoles occasionally show a slightly different daily rainfall.  And of course a different monthly, etc.

Any thoughts on which console I should believe?

[LFWX]

I've also wired a second console using these instructions.

Sometimes the console closest to the ISS, which is also the console NOT connected to the computer, will show slightly more rain. I always use it's readings to adjust the console which is connected to the computer. Obviously the console at the computer is missing a packet or two of data which contain rainfall info.

For anyone else considering this setup, here are some photos.

Close up of the wiring (ignore the ivory colored wire, it's the phone line to the kitchen):
http://www.flickr.com/photos/30112397@N06/2852698236/in/set-72157607366155684/

Overall layout of my system:
http://www.flickr.com/photos/30112397@N06/2879504922/in/set-72157607366155684/

Hope this is helpful,
Mike

[dalecoy]

I decided to believe the console with the higher rainfall reading, too.  In my case, it happens to also be the one that has the logger (and is closer to the ISS).

I see that you show your two consoles wired in parallel - and that's how I wired mine, also.  In theory, they should be wired in series (and that might or might not make the rainfall identical), but I chose the parallel hookup for simplicity and reliability.

Of course, the inside temperature/humidity and the barometric pressure readings are going to be different for each of the consoles.  And there are manual corrections that must be done to the "extra" console.  But I find it quite nice.

The "wiring" would be easier with the wireless VP2 - but I'm convinced that it's less trouble afterward.

I'd appreciate it if someone who has multiple wireless consoles would report whether the rainfall (and other) readings are always the same.

[Bushman]

Why on earth would they not be the same?  The datastream is  broadcast and anyone with the station switch set correctly will get the exact same data, no?

[kray1000]

The second console could be out of range of the ISS (not likely with a VP2 though).

The wireless console can act as a repeater transmitter, so console #1 would send the (same) data to console #2.

[LFWX]

I see that you show your two consoles wired in parallel - and that's how I wired mine, also.

I wired this way per the info I was able to find about RS-485
http://www.lammertbies.nl/comm/info/RS-485.html

I also see at this same site - twisted pair wiring may work better than the flat cables supplied by Davis.
My setup also has the cable for the ISS running next to the cable for the data logger (inside a plastic wire loom), so this be part of the problem.

The "wiring" would be easier with the wireless VP2 - but I'm convinced that it's less trouble afterward.

That was my logic also! It's why I switched my computer from wireless network, to wired network - too many times of seeing 'excellent signal strength' and 'unable to connect' at the same time.

[dalecoy]

Why on earth would they not be the same?  The datastream is  broadcast and anyone with the station switch set correctly will get the exact same data, no?

Here's what I believe is happening.

Any receiver can certainly "miss" a data point.  Because of signal strength, noise (induced in console wiring and/or local to one console), etc.  The factors are a bit different for "wired" and "wireless", but transmission/reception is not "guaranteed".

For most of the data transmitted, that makes little difference.  For example, temperature.  If a console doesn't "get" the temperature in this interval, it just "remembers" what it last got.

However, rainfall is different.  Each "click" of the bucket is transmitted.  The console "counts the clicks", and that's the amount of rainfall. 

If one of the (multiple) consoles misses a "click", and another one gets it, there's a difference.  There's no way for the console to make it up.

That's a bit simplistic, but perhaps it helps.

[johnd]

The ISS does remember the total of recent clicks and transmits this total in a rain packet. But two things can happen to make two consoles seem to disagree:

1. A console can miss a packet. Then the two consoles will disagree until a later packet has been successfully received by both consoles. So this is a temporary disagreement.

2. (The commonest one) The time is not synchronised between the two consoles and hence the midnight time point (at which the daily rainfall rezeroes) is not passed simultaneously by both consoles. The greater the discrepancy in time the more difference in rainfall totals may be seen if rainfall spans the midnight time points.

NB This also assumes that both consoles are correctly configured in other ways, eg one console could be set to 0.01" increments while the other had been inadvertantly changed to 0.2mm.

[LFWX]

The ISS does remember the total of recent clicks and transmits this total in a rain packet.

The total of recent clicks would ONLY be those sent to the ISS by the rain bucket since the last time the ISS sent a rain info packet. Correct?

Then the two consoles will disagree until a later packet has been successfully received by both consoles. So this is a temporary disagreement.

Is the ISS resending info? I was under the impression that the only info sent would be new rainfall. I've never had the problem correct itself.

The time is not synchronised between the two consoles and hence the midnight time point (at which the daily rainfall rezeroes) is not passed simultaneously by both consoles. The greater the discrepancy in time the more difference in rainfall totals may be seen if rainfall spans the midnight time points.

Does the ISS even have a way of knowing what time it is (required before it can send a daily total to the console)? Isn't the ISS send only, not send and receive?

Someone correct me if I'm understanding this incorrectly!

[johnd]

The total of recent clicks would ONLY be those sent to the ISS by the rain bucket since the last time the ISS sent a rain info packet. Correct?

No, AIUI the ISS circuitry has a counter for rain clicks running up to 64 or 256 or some such relatively small number. It's the current value of this counter that get's transmitted. So it's not a daily rainfall amount that's transmitted by the ISS, just the counter value since the last zero value was reached (the counter rolling over to zero when it reaches maximum). This is exactly the mechanism that's intended to ensure that if reception of a data packet is missed at the console, then it won't affect the correct rainfall total once a later packet has been successfully received.

Is the ISS resending info?

That's how Davis describe it - ie the current counter value is resent at regular intervals and this then increments the console value. (Of course if the value that the console is using as a reference is wrong then there's not enough information transmitted to correct major discrepancies AIUI.

Does the ISS even have a way of knowing what time it is (required before it can send a daily total to the console)? Isn't the ISS send only, not send and receive?

As above, it's not the ISS that resets daily rainfall at midnight, it's each individual console. You're right - the ISS doesn't know what time of day it is. But as per my original reply if the time on two consoles is not synchronised then they can easily show different rainfall totals under certain rainfall conditions.

[LFWX]

the ISS circuitry has a counter for rain clicks running up to 64 or 256 or some such relatively small number. It's the current value of this counter that get's transmitted. So it's not a daily rainfall amount that's transmitted by the ISS, just the counter value since the last zero value was reached (the counter rolling over to zero when it reaches maximum). This is exactly the mechanism that's intended to ensure that if reception of a data packet is missed at the console, then it won't affect the correct rainfall total once a later packet has been successfully received.

Thanks! That's very nice info to have.
A counter which 'rolls over' certainly makes a lot of since.