Topic: Hacking extra stations on a cabled VP2 experiments

[SLOweather]

I don't recall if this had been tried and posted before, so I did a little experimenting last night, just for the heck of it.

I have 3 or 4 spare cabled SIM boards laying about. on one, I scraped the conformal coating off the solder pads for the DIP switch location and soldered a jumper across the pads for position 3, thereby setting the station ID to 2. I plugged a temp probe into the temp hum jack.

On a cabled console, I left station 1 on and ISS, and set station 2 on and temp only.

Plugging in just station 2 and I did get a temp reading on station 2 on the console.

After that success, I cobbled up a 3 way RJ tap out of 3 wall jacks to connect the 2 SIMs to the console. With all 3 connected, the ISS read OK on the console, but the Station 2 temperature stuck at the last reading and never changed. Unplugging the ISS let station 2 read again. Both stations had blinking green LEDs, and the console had good batteries.

I think I might try setting the ISS and the console to a different number and see what happens, in case the firmware does something special with station 1.

[dalecoy]

Interesting experiment.  Hooking the power (from the console) up to both ISS boards in parallel should be right.

However, the communications protocol is the "problem" - and particularly assuming that you hooked those in parallel.  With a parallel connection, the ISS boards are "fighting" each other.  [Footnote: it "works" to hook up multiple consoles to one cabled ISS - but that's not what you're doing, and is just an "accident" anyway]

The protocol is actually RS-422, as I recall.  At any rate, it's a serial protocol.  Try hooking the communication connections all in series.  I'm not at all sure that will work - but it's a better shot than parallel.

-----ISS1-----ISS2-----Console---
|                                                |
------------------------------------

[SLOweather]

Looks like you are correct. For some reason, I thought 422 was multidroppable, probably confusing it with 485.

From Wikipedia:

RS-422 cannot implement a truly multi-point communications network such as with EIA-485, however one driver can be connected to up to ten receivers.

I've doe the 2 consoles thing before. Now if I just had 3 RS422-rs485 converters...

Interesting experiment.  Hooking the power (from the console) up to both ISS boards in parallel should be right.

However, the communications protocol is the "problem" - and particularly assuming that you hooked those in parallel.  With a parallel connection, the ISS boards are "fighting" each other.  [Footnote: it "works" to hook up multiple consoles to one cabled ISS - but that's not what you're doing, and is just an "accident" anyway]

The protocol is actually RS-422, as I recall.  At any rate, it's a serial protocol.  Try hooking the communication connections all in series.  I'm not at all sure that will work - but it's a better shot than parallel.

-----ISS1-----ISS2-----Console---
|                                                |
------------------------------------

[belfryboy]

You might also try flashing the console with the wireless firmware. I would be surprised if the console with cabled firmware would be "happy" with the delayed transmissions of the ISS set at different staion IDs

[dalecoy]

Yeah, in practice with RS-422, you can hook up several consoles in parallel with one ISS (which is how I've got mine connected, for convenience)...

...in theory the multiple receivers should be connected in series with one transmitter.

And since RS-422 is a differential protocol .......  if Davis implemented it correctly, you're probably out of luck without converting to another protocol.

[saratogaWX]

Wow, RS-422 .. a LONG time ago while working for Fairchild Semiconductor, I helped define that standard with EIA TR30.1 subcommittee and was a representative to ISO TC97-SC6 in Paris where standard V.11 came to pass.
Wrote a small book at Fairchild (The Interface Handbook - Line Drivers and Receivers, published 1975).

It still exists in part, but now as app notes from Texas Instruments who bought National Semiconductor who bought Fairchild Semiconductor.
http://www.ti.com/lit/an/snla026a/snla026a.pdf
http://www.ti.com/lit/an/snla027b/snla027b.pdf
http://www.ti.com/lit/an/snla028/snla028.pdf
are all that survive now.

My favorite chapter was http://www.ti.com/lit/an/snla028/snla028.pdf where the 'eye pattern' was used to do signal quality estimates, and my data was used in the EIA/TIA and ISO standards  After I left Fairchild in 1981, the subsequent publications of the app note(s) conveniently filed off my name from the masthead of the book and instead published the chapters as separate app-notes (without attribution).  

Don't ask me questions about it anymore.. the neurons holding the Electrical Engineering part of my career have long since atrophied