Federrico: Yes, I have bought one from pvelectronics. It will arrive on Friday (hope)

Jarkman, this one?

http://www.dealextreme.com/details.dx/sku.39753

Is it a good buy?

Mine is coming from the same shop. I will tell my results.

My DS1307 RTC has an error of +4 seconds every day. That is 4*365=1460 s = 24.3 minutes every year. :'(

You can try this
[media]http://www.youtube.com/watch?v=X0IGvHP4nnk[/media]

Yes, but you are not sure you will get time sync the next time you turn off and on arduino.
If you use a RTC+battery you will always have a time source.

That's the reason why I will use a combination of a ds1307 and a dcf77 receiver.
DS1307 to keep time and dcf77 to make corrections.

The dcf77 module will sync the RTC every start of minute found.

Jarkman, are you using any pull-up resistor like:
 http://gonium.net/md/2006/11/05/arduino-dcf77-radio-clock-receiver/
?

Thanks

OK.  PON = ENABLE.

Is there any special reason to use analog instead of digital?

Thank you very much.

Hello.

I'm very interested in the DCF77 Time Module and I have order one from PVElectronics, but I have some questions about its technical data:

Supply voltage range: Max 5V, Min 1.8.
What voltage are you using? 3.3 or 5v?

PON Input Level High: Min 0.85.
Is this enough to arduino? is some interface transistor needed?

Thank you very much.

With XBee you can simulate a serial connection without cables.

I will try to convert rs485 to tx/rx and then send it trough XBee.

Thank you.

Thank you.

Which one is the most common in PLC and other industrial stuff?

Hello.

rs485 full or half duplex: Which one is the most usual in industrial environment?

With full-duplex I will use a second twisted pair but with half-duplex I need a extra pin to control sending/receiving.
Also full-duplex transceiver is more expensive.

I'm planning to use MODBUS as protocol and MANGO M2M as SCADA to control over 20 slave nodes separated 2 meters (40 m) with a Master node separated 50 m from first slave.

How much is a single pair and a double pair cable for rs485?

Is possible to use XBEE to link the nearest slave and the master? Is possible to do that with half-duplex rs485?

Thanks in advance.

MCP609 has +vcc and gnd only. Am I wrong?

Well you know enough to spot the gain of the inverting amplifier was wrong.

Am I right?  :

Note that Fig 5 is not a full schematic, you will need a split power supply as well as some decoupling and a decent layout. That is don't expect it to work well on solder less bread board.

split power supply:
I think you mean " a good Vref and GND". Can I use a 5v precision voltage reference for this circuit and for Arduino Aref?