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There are lots of examples around how to connect with an NTP server, but I do not see how to find such an IP-address. From the examples I conclude I need to find it on for example pool.ntp.org, but I do not even see how to get IP-addresses out of there myself, let alone to let my Arduino do it. Of course I looked at the How do I use pool.ntp.org page, but it doesn't seem to say anything about finding IP-addresses.

Questions

  1. Is it possible to let my Arduino find a working NTP server (using the EtherCard library), and if so, how?
  2. All the examples I saw have an NTP server IP address hard coded, isn't that a bad practice and also a bad idea for a longer running project?

The code I currently find the easiest to understand is from the Arduino forum, and has an IP address hard coded.

I have an Arduino Nano ATmega328 with a ENC28j60 ethernet shield, and therefore use the EtherCard libray. I do know of existence of RTC devices but I would prefer NTP.

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  • You need to perform a DNS lookup in order to convert the host name (e.g. "pool.ntp.org") into an IP address. Doesn't the EtherCard library have a facility for that?
    – Edgar Bonet
    Commented Jul 5, 2016 at 13:57
  • @EdgarBonet That sounds logical, indeed EtherCard can do that, googling it it would be something like if (!ether.dnsLookup(website)) { Serial.println("DNS failed"); } ether.printIp("Server: ", ether.hisip); but I'm new to the ethernet connections so I need to find out how to get an ip address out of that to use later in the code...
    – PHPirate
    Commented Jul 5, 2016 at 14:06
  • I found an ip address with the code in the form of a string, but didn't manage to convert it to an array even with stackoverflow.com/questions/35227449/… so I'm leaving that for now. This question is solved I guess, although I am not sure of course if the ip is a correct one because I can't test it.
    – PHPirate
    Commented Jul 5, 2016 at 14:55
  • ether.hisip is not a string, it's an array of 4 bytes.
    – Edgar Bonet
    Commented Jul 5, 2016 at 15:05
  • @EdgarBonet Oh indeed you are right! That solves my whole problem, thanks a lot! I was tricked into thinking it was a string by what ether.hisip printed to, but now I see that's why ether.printIP was used.
    – PHPirate
    Commented Jul 5, 2016 at 15:26

1 Answer 1

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The EtherCard library offers a method called ether.dnsLookup(host) where you ask it to look up the IP address for you.

etherCard.dnsLookup("pool.ntp.org");

...only that might fail, so it returns a false:

if (!etherCard.dnsLookup("pool.ntp.org")) {
    // Error! Do something!
    return;
} // if

But if it works...

if (!etherCard.dnsLookup("pool.ntp.org")) {
    // Error! Do something!
    return;
} // if
// At this stage, dnsLookup() worked...

// Can now connect to IP adress in etherCard.hispip

Now: please note that ntp.org would prefer you to use a more precise locale than pool.ntp.org. If you're going to distribute your application worldwide, then that's fine. But I always use au.pool.ntp.org because I'm in the Australian region. There are others that you can/should use instead.

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  • Thanks for writing Edgar's suggestion into an answer, the locale is a nice addition!
    – PHPirate
    Commented Jul 5, 2016 at 14:56

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