As with all these things it was a bit more complex than it seemed. Yes I found a stick that worked with wvdial plus tried a lot of others that didn't. Generally they would get as far as making a connection then the ppp daemon would croak. I tried reading up about ppp and associated options but it all just made my elderly head spin.
So I went back to the wifi/hotspot solution which works every time. You need a kb/screen at the beginning to manage the process where it finds the hotspot and you enter the SSID and PSK. After that the connection is automatic. The only problem is if the power is off for a while and the hotspot battery goes flat, then you have to press the start button when it is repowered. Hard when it is in a box up a pole. I Fixed that by gluing down the start button .... ugly ... I know. Works though.
One other useful thing. I powered the Pi using a 5v wall wart at the bottom of the pole. Everything worked, but it was a bit unreliable. Cameras were disconnecting and reconnecting and stuff. So now I run 12v up the pole and have a $3 buckie supply in the box to drop t to a regulated 5v. Seems to have stabilised things.
I've got a Pi 2 running a weather station on the Coromandel Peninsular (the northern most one on the MetService YourWeather thing). Nearest cell tower is a Spark one on Great Barrier Island, about 20km off the coast. The Sierra Wireless 306 with a big external yagi antenna seems to work quite well for this. wvdial is setup in /etc/network/interfaces so everything comes back automatically after a reboot, etc.
For remote admin I use openvpn so despite being 200km away this Pi just appears on my home network like any other machine.
OpenVPN. I've heard of it .... My son keeps telling me I should be using it. Does it use much cellular data in "idle" mode?
I got the ZTE180 and Huawei E3531 to work. But there were hiccups. A "local" E3531 worked - an "unlocked" one from AliExpress didn't. I was looking for a general sort of solution so I could get a few of these stations out there at airfields. The hotspot/wifi thing works faultlessly with no driver issues. The only drawback is that I can't do SMS's with it. Not a biggie.
I suspect the hotspot is a bit of a power hog - 250 odd mA at 5V or so. Not a problem while I am running it off mains. The whole thing draws 420mA at 12V which will be about 1000 mA at the stepped-down 5v. A bit on the hungry side for a solar install if I wanted to do one.
ianboag: OpenVPN. I've heard of it .... My son keeps telling me I should be using it. Does it use much cellular data in "idle" mode?
I got the ZTE180 and Huawei E3531 to work. But there were hiccups. A "local" E3531 worked - an "unlocked" one from AliExpress didn't. I was looking for a general sort of solution so I could get a few of these stations out there at airfields. The hotspot/wifi thing works faultlessly with no driver issues. The only drawback is that I can't do SMS's with it. Not a biggie.
I suspect the hotspot is a bit of a power hog - 250 odd mA at 5V or so. Not a problem while I am running it off mains. The whole thing draws 420mA at 12V which will be about 1000 mA at the stepped-down 5v. A bit on the hungry side for a solar install if I wanted to do one.
my setup is nzfi.avmet.nz ....
IB
I don't know how much cellular data openvpn itself uses but according to vnstat my entire setup tends to average ~70MB/month when I'm not interfering with it - easily fits into Sparks minimum data pack. I think when not in use openvpn should just be sending a keep-alive packet every 30 seconds (80,640 every 4 weeks) and restarting the connection every hour when keys expire (672 every 4 weeks) so its usage should be fairly minimal compared to the weather station which can send as many as 975,744 updates in a four week period to the server in California that runs the web interface (http://weather.zx.net.nz/s/sb/). OpenVPNs settings can be adjusted to send keepalive messages less frequently and I assume key expiry can be adjusted too, all of which would reduce its idle data use further.
I've used Huawei ones like the E3531 before and it always seems to be a bit of a pain getting them to appear as a modem instead of a flash drive full of windows drivers. As for power use - 3G modems seem to be power hungry in general, especially when reception is poor (I currently have -93dBm, RSSI of 10 - just barely "OK"/2 bars). I suspect this may have been the cause of a few Pi crashes last year so I moved it onto a powered USB hub after Christmas.
The REAL simple solution to talking to devices that are on cellular .... is dataplicity.com - the Team Viewer of the Pi world! It's even free. I wouldn't care if it wasn't ....
You go to the dataplicity website and create an account. Then you go to the pi and type in a line of gibberish which sends it in circles for about 10 minutes.
Put the device on the Net somehere - behind a firewall is OK, on a LAN is OK, cellular is OK, ethernet would be fine. The system does not care what the Pi IP address is. There is no port forwarding stuff. You can even move it around .....
Then you go the the website, sign in and there it is in a list "My Devices". Click on the device and bingo you have an SSH connection. Just like that.
Sort of like OpenVPN with all the geeky stuff removed I guess.
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