Can't reliably establish connection w/ DreamPi modem

[Tengato]

Hi, I've gotten my Dreamcast online successfully a few times now, but getting the two modems to establish a connection has an increasing failure rate... For example, I boot the DreamPi, and soon the modem's two lights turn on and begin rapidly flashing - which I take to mean it's ready. Then I initiate the connection on the Dreamcast, (I use PSO v2, Quake 3, or Web Browser 2.6) and it dials the number. When it works, I see one of the modem lights go out and the other go solid on. But about 75% of the time, nothing happens, and the Dreamcast software reports a failure to connect.

I have a standard DIY line voltage inducer circuit attached, the USB modem is an off-brand StarTech.com I got on Amazon; I wasn't sure if the modem would work with the DreamPi, but it did give me several connections early on so that should mean DreamPi can see it and operate it... Once the connection is established, it's very stable. I just wonder if there's something I can do to make the initial exchange more robust, or if there's some way to troubleshoot what is happening...

[Tengato]

I found a clue that might be helpful: when I cannot connect, if I disconnect and reconnect the 9V battery on the line voltage inducer, the connection will be successful on the next attempt.
This is a nice discovery because I can get it to work when I need it to, though I can't explain exactly what is going on. My best guess is that when the capacitor is fully charged, the signal cannot pass through without getting clipped. Removing/reconnecting the battery allows the capacitor to discharge, and for a short while there is some 'wiggle room' where the signal can be established. Once there's a signal in the line, the capacitor won't seize up like that...

[leotju]

I’m not an expert on this, but are the capacitor and resistor in your LVI circuit to the specs listed in most guides online? (Can’t remember what they actually are right now though lol). That very much sounds like an analog power-related issue. Also, I use a DC boost converter set to boost to 9V wired to the Pi’s USB 5V output, and it works perfectly. It’s more elegant than a 9V battery (or two) hanging off the phone cable. The specific boost converge I used can go up to 24V, so it would be suitable for the 18V necessary for PAL modems. If you’re handy with a soldering iron, it’s worth considering.

[Tengato]

I used a 390Ω resistor and 0.47μF 50V electrolytic capacitor, using this design:
https://www.segasaturnshiro.com/guide-b ... e-inducer/
(I even made a second one as a sanity test...) I wonder if 390Ω is a little high, it was the closest I had on hand, but I just noticed that they list the range as 330-380. I read that the current supplied by the phone service can vary a lot though, so it should be ok? I wanna say this is just an annoying weakness with the modem I got.

[Tengato]

I have resolved this problem - the issue was insufficient current. Using a 330Ω resistor helped - but just as importantly, by switching to a fresh 9V battery, I haven't had a failure yet. It was one of those situations where the battery tested fine on the meter, but under load the voltage dropped just enough that it wasn't effective...