[dougc]

I posted this over at ReefCentral, but it might be useful to someone, so I am posting it here, too.
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I just wanted to share what I learned about connecting a non-sanctioned modem to an AquaController II. I got it to work, but it took a few days of messing around.

I did purchase the Neptune modem cable, since it would not save that much money to try building one myself. First, I tried using an el-cheapo $35 modem. Inevitably, I tested it once using the Test Page from the setup menu on the AquaController and it worked fine. I then mounted the modem, routed the cables, zip-tied everything down, and proudly tried a test page again. The test did not work and after numerous attempts, I did get it to work a couple more times, but apparently only by chance. Pull it all down.

I remembered that the only picture I had ever seen of the Neptune modem looked like a US Robotics Sportster, a type of modem that we have many of in our modem graveyard at work (God bless DSL). I took one home yesterday to give it a try. It was an old 33k model. Hooked it up and could not get it to work. I could see that the AquaController was sending something, but the modem never went off hook and dialed.

Most US Robotics modems, unlike my cheapo model, have a set of DIP switches to set the configuration of the modem. This is in addition to the changes that can be made using the AT command set. The settings include those that control response codes (verbal/numeric), autoanswer, command echo, etc. Depending on what combination of DIPs I chose, I noticed that the Send and Receive lights would sometimes go nuts when I tried the Test Page. This would go on for a while and then stop. Hmmm...Clue #1.

I wanted to see what the AquaController was sending to the modem in the way of commands, so I fired up Hyperterminal on my computer, hit Test Page, waited for SD and RD to go nuts, and quickly switched the cable from the modem to the serial port on the computer. What I saw streaming across the Hyperterminal screen was the configuration data and my program for the AquaController. Apparently, either the echo of commands or a response from the modem was also a command that the AquaController recognized as a request to download the configuration. Clue #2.

Leaving the AquaController hooked to Hyperterminal, I did another test page to see what the Test Page sent. Real simple. It does no configuration, just a dial:

ATDT[my pager #],,,,,[AquaController config]

I noticed that when I hooked up the modem to my computer, the DTR (Data Terminal Ready) light was on, but when hooked to the AquaController, it was not lit. Normally, a modem expects the DTE (computer) to provide the DTR signal. The absence of DTR is meaningful to a modem, depending on how the modem is configured. Toggling of DTR in most cases will cause the modem to hang up the line and possibly return to a command-line mode. Clue #2.

I looked at the Neptune serial cable wiring and the cable does not feed DTR on the DB9 connector (pin 9), explaining the lack of DTR. One of the DIP switches on the US Robotics modems controls DTR. Set one way, DTR is forced on, just what is needed in this situation. Another pair of DIPs lets you turn off the responses and command echo [FYI, this can also be set through AT command set]. Once I set these options, the test page worked like magic.
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Summary: Force DTR on, set command echo to OFF, and turn off Reponse codes on the DIP switches.
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The gotcha here is that you must have a modem that lets you configure the DTR setting through DIP switch. This is not something that can be done through the AT command set. The good news is that older US Robotics modems can be picked up for about $10 on ebay.

I don't know whether these settings will work if you wish to dial into and control the AquaController, but I can't do that anyway, so I haven't tried.