[ntp:questions] almost decided which new PPS GPS to buy

David J Taylor david-taylor at blueyonder.co.uk.invalid
Mon Mar 5 09:29:56 UTC 2012

"unruh" <unruh at invalid.ca> wrote in message 
news:jaQ4r.26824$VR6.8194 at newsfe14.iad...
> Again, almost no serial ports need this. They work fine off TTL level.
> While it is true that the standards say -5 to 5 V almost all accept
> 0-5V. Now you can try it, and if it does not work, then go for the two
> wire solution. But if you are at all klutzy with a soldering iron, try
> the first first.

If you know you will have a short connection, 2 m or less, for example, 
likely you will be OK with TTL levels.

But if there is a chance you will have a longer connection (10m or more), 
or the cable will be going past some electrically noisy appliance, or of 
you need to move the GPS to the loft or a substantial distance away, why 
take the risk of TTL levels when for the effort of soldering one extra 
wire you can have RS-232 levels intended for line driving?

The owner's choice, of course.


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