Mat's Hideout rants, raves, rhymes, reviews

After noip.com and dyndns.org shut their doors to all but non-paying customers, I spent many years without being able to reliably access my home network from outside. Of course, it was always possible to do without dynamic DNS by making a note of the current IP address and use this for as long as the address stayed the same, but sods law I would *really* need to access home the day that the router was upgraded remotely or the address expired or whatever.

Over these years I looked at various options, and almost settled on installing BIND9 and using nsupdate on a remote machine and writing a script on the local network to check-in periodically.

This seemed like a good option because I already pay monthly for a linux VPS so there was no extra outlay. Deep down, though, I knew it was overly complicated and would probably break someday because I don’t have the time to maintain my VPS in a “mission critical” way, or I’d rebuild the server and forget it took me 4 hours to setup the solution, thus ending up not having it for another 6 months because I couldn’t be bothered to go through the effort again.

Turns out there was much more of a tidy solution for me. I use Linode.com to host my VPS, and I also use its excellent DNS manager control panel for all of my domains. Sure, you can use the DNS manager of your domain registrar and create A records and the like to point to your Linode’s IP, but it’s so much nicer pointing your NS servers to Linode and managing all your DNS settings from Linode. The interface is designed beautifully, the account security is top-notch, not to mention there’s a very sweet iPhone app that makes creating records / cloning zones a breeze.

I digress. My solution involves creating a Linode API key, pulling-out the domain and resource IDs from Linode, then having a powershell script which runs on a local Windows box update these when it detects a change of address.

I won’t bother going in to the former as you can work that out, but the latter is certainly something worth sharing here.

After nicking the IPChangeNotify powershell script from somewhere on the web, I discovered a whole load of reliability weaknesses, which I’ve pretty much accounted for. Without further ado, here’s the spec of my updated script and solution as a whole

• relies on Windows task scheduler
• (ironically) uses dyndns IP address checker at http://checkip.dyndns.com/
• if for some reason the above doesn’t respond in a timely manner, it waits, tries again, waits, etc.
• updates are of course made securely, over https
• email notifications telling you a whole load of useful info such as:
  • how many attempts it took to discover the ip address
  • number of milliseconds it took to discover the address (for fun / to help diagnose problems)
  • old ip address
  • new ip address if changed
  • response from Linode API to confirm that the A record was updated
  • email subject based on change / success / failure to allow for sensible rules in Gmail
• write-out the IP address to Dropbox (added bonus – you get a little Windows notification when this text file is changed) – just in case something goes wrong and you can’t be bothered to sift through notification emails

All you need to make this work is:

• a Linode account
• Windows machine on your local network that stays on all the time
• the below script

(Apologies for the godawful formatting, but it should copy/paste okay!)

$scriptpath = $MyInvocation.MyCommand.Definition
[string]$dir = Split-Path $scriptpath
set-location $dir

$oldip = gc .\ip.txt
Write-Host “IP stored in Dropbox: $oldip”
Write-Host “Getting current IP…”

$firststartTime = get-date
$webpage = (New-Object net.webclient).downloadstring(“http://checkip.dyndns.com”)
$firstendTime = get-date
$timetogetpage = ($firstendTime – $firststartTime).TotalSeconds
$currentip = $webpage -replace “[^\d\.]”
Write-Host $currentip
Write-Host “That took” $timetogetpage “seconds”

if ($timetogetpage -le 2) {
$triestext = “(on first attempt)”
} else {
$triestext = “, not on the first attempt:`n`nTry 1 ($currentip) = $timetogetpage`n”
}
$tries = 1
while ($timetogetpage -gt 2) {
Write-Host “Let’s try again”
$subsequentstartTime = get-date
$webpage = (New-Object net.webclient).downloadstring(“http://checkip.dyndns.com”)
$subsequentendTime = get-date
$timetogetpage = ($subsequentendTime – $subsequentstartTime).TotalSeconds
$currentip = $webpage -replace “[^\d\.]”
$tries++
$triestext = $triestext + “Try $tries ($currentip) = $timetogetpage `n”
Write-Host “Try $tries ($currentip) = $timetogetpage”
}

$smtpServer = “smtp.gmail.com”
$sender = “sender-email@gmail.com”
$users = “recipient-email@gmail.com”, “anotheruser@gmail.com”
$subject = “”

# change the below to match the ID of the given record
$resourceid=’1234567′
# change api_key and domainid below to match your Linode.com API key and ID of the domain
$updateurl=”https://api.linode.com/?api_key=abcdefg&api_action=domain.resource.update&domainid=123456&resourceid=$resourceid&target=$currentip”

if ($timetogetpage -lt 3) {
if ($oldip -eq $currentip) {
# Discovery success – IP stayed the same (ideal case)
$subject = $subject + “IP address found: $currentip. No change! (discovery took $timetogetpage seconds)”
$body = “Old IP = $oldip`nNew IP = $currentip`n`nNo change!`n`nDiscovery took $timetogetpage seconds $triestext”
Write-Host “Not updating the file” -ForegroundColor Gray

} else {
# Discovery success – IP changed (important case)
$subject = $subject + “IP change detected: $currentip. Discovery took $timetogetpage seconds”
$body = “Old IP = $oldip`nNew IP = $currentip`n`nWe updated the DNS!`n`nDiscovery took $timetogetpage seconds $triestext”
$currentip | Out-File .\ip.txt -Force
Write-Host “New IP saved in file is: $currentip” -ForegroundColor Green
}

Write-Host “Updating DNS…”
$updatewebpage = (New-Object net.webclient).downloadstring($updateurl)
$body = $body + “`n`nOutput of the DNS Update service:`n`n$updatewebpage”
if ($updatewebpage -like “*Invalid*”) {
$body = $body + “`n`nLinode response: DID NOT UPDATE. Check Linode.com.”
} else {
$body = $body + “`n`nLinode response: UPDATED”
}
Write-Host “Output of the DNS update service: $updatewebpage”

} else {
# Discovery failed
$subject = $subject + “IP address kept as $currentip (discovery failed and took $timetogetpage seconds)”
$body = “Old IP = $oldip`nNew IP = $currentip`n`nI’m suspicious, discovery took $timetogetpage seconds $triestext”
Write-Host “IP address supposedly found, but it took $timetogetpage seconds” -ForegroundColor Red
Write-Host “Keeping the current IP: $currentip” -ForegroundColor Red
}

# Finally send the email
Write-Host “Sending an email now…” -ForegroundColor Green
foreach ($user in $users) {
Write-Host “Sending email notification to $user” -ForegroundColor Green
$smtp = New-Object Net.Mail.SmtpClient($smtpServer, 587)
$smtp.EnableSsl = $true
$smtp.Credentials = New-Object System.Net.NetworkCredential(“sender-email@gmail.com”, “email-password”);
$smtp.Send($sender, $user, $subject, $body)
}

Here’s a quick hookup guide and sketch to get the ER-OLEDM032-1W display to work with Arduino. We are going to use the u8g library to drive the OLED.

The ER-OLEDM032-1W is a 256×64 graphic OLED module costing $26.56. White on black. I bought mine from eBay although the Chinese brand BuyDisplay.com sells them directly.

There are two versions of the display, one including the integrated PCB (above) and one without. We want the above one, with integrated PCB. Make sure you purchase the one with the M in the part number.

Here’s a link to the data sheet.

About the part number:

• ER stands for “East Rising” the manufacturer
• OLED stands for OLED: “organic light emitting diode”
• The M stands for “module”. I think. They do two versions, the one with driver board (adapter board) which is this one, and one without the driver board which doesn’t have that M. Confusingly they call the one without a driver board module an OLED module as well. Either I’m wrong or their naming convention is confusing. Or both. Either way you probably want the one with the M, it has an integrated PCB.
• The 032 stands for 3.2 inch, corner to corner
• Not sure what the 1 stands for, they all seem to have it
• The W stands for white, they have other colours (yellow, green blue)

To use the display with u8g library and Arduino you must swap the tiny resistor on the back in position R18 to the position R19. Do this with a steady hand, some really good tweezers and a soldering iron.

ER-OLEDM032-1W Display hookup
swap 0 ohm resistor from R18 to R19 on rear of display
1> gnd
2> 3.3 OR 5 ok
4> level conv – arduino 4 (clock)
5> level conv – arduino 5 (data)
7-13> gnd
14> level conv – arduino 7 (command data select i.e. D/S)
15> reset – this needs to be connected to +5v
16> level conv – arduino 6 (chip select)

For the level converter I used this very cheap module, a clone of something by Adafruit: http://www.ebay.co.uk/itm/Pop-IIC-I2C-Logic-Level-Converter-Bi-Directional-Module-5V-to-3-3V-For-Arduino-/381311755120?hash=item58c7f3a370

And here’s a sketch. I ripped this from a larger sketch I have been working on and haven’t tested it, but it should all be about right.

#include "U8glib.h"

#define oledClock 4 // OLED
#define oledData 5 // OLED
#define chipSelect 6 // OLED
#define commandDataSelect 7 // OLED

U8GLIB_NHD31OLED_2X_GR u8g(oledClock, oledData, chipSelect, commandDataSelect);

void setup()
{
// Setup U8G
if ( u8g.getMode() == U8G_MODE_R3G3B2 ) u8g.setColorIndex(255); // white
else if ( u8g.getMode() == U8G_MODE_GRAY2BIT ) u8g.setColorIndex(3); // max intensity
else if ( u8g.getMode() == U8G_MODE_BW ) u8g.setColorIndex(1); // pixel on
else if ( u8g.getMode() == U8G_MODE_HICOLOR ) u8g.setHiColorByRGB(255,255,255);

....

}

/******************************************/
/* CONTROL DRAWING */
/* --------------- */
/******************************************/
void drawControl(void) {

** insert logic to draw different things here, e.g. as follows **

// Draw current room light level
if (showlightlevel == 1) {
u8g.setFont(u8g_font_6x10);
u8g.drawStr(178, 30, "Currently");
if (lux < 20) {
sprintf (buff, "%i%s", lux, " (dark)");
} else if (lux < 100) {
sprintf (buff, "%i%s", lux, " (med dark)");
} else if (lux < 400) {
sprintf (buff, "%i%s", lux, " (med bright)");
} else if (lux < 10000) {
sprintf (buff, "%i%s", lux, " (bright)");
}
u8g.drawStr(178, 40, buff);
}
}

void loop()
{
u8g.firstPage(); // START U8G
do { // START U8G
drawControl(); // START U8G

** insert the rest of your sketch that does stuff **

} // END U8G
while( u8g.nextPage() ); // END U8G
}