RFM70

I have been designing a 24-hour digital clock system that retrieves an external wireless signal from places such as NPL who send a signal at 60kHz giving the time and date as an analogue RF signal. This signal is to be sent to the RFM70 transceiver, which operates at 2400MHz to and then demodulated into binary by means of frequency-shift keying.

A few things i need to know include:

  • Is the signal being sent from the external souce (e.g. NPL) compatable with the RFM70's operating frequency, if not then are there any other external sources that provide the date/time that run off the required frequency of RFM70.
  • How is the signal from these external sources sent? Are they sent as a sequence of RF signals that provide the correct time which can be demodulated into, say, an 8-bit binary sequence which can then be displayed on several 7-segment displays?
  • How can the output of the binary sequence be manipulated to display on 7-segment displays? As in, can i use an LM8560 digital counter in some way to display the correct time according to the external wireless transmission?

I'm very new to using Arduino's and am not very familiar how a lot of them function completely but have gathered as much info as i can with this and I'd appreciate any help at all with this project. Thanks in advance :slight_smile:

Perhaps I don't understand what you are proposing, because it seems to me you answered the first question yourself. 60KHz and 2.4GHz are a long way apart, I doubt any device designed for one will be compatible with the other...

There are receiver modules available on eBay for receiving those 60KHz time signals like this:

http://www.ebay.co.uk/itm/WWVB-Atomic-Clock-Receiver-Module-Fort-Collins-60KHz-Receiver-/231073521325?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item35cd0e1ead

Not sure what your RFM70 is doing in this project.

The other aspects of the design, 7 seg displays etc. are all do-able.

As for the lm8560, it seems to be a clock ic and I'm not sure how or if you really need to interface it with Arduino. Arduino can drive led displays directly or via a driver ic like saa1064 or max7219. How many digits do you want and what size?

Paul

Apologies, you're write i did answer my own question without realizing haha. But are there any other open source time/date transmitters like NPL that run in the 2.4GHz+ range? I'll have a look into the modules on eBay thanks.
The RFM70 is receiving the wireless signal from NPL (or a similar company) that gives us the time/date and is converting the radio frequency signals from NPL to a digital binary signal which is then to be sent to another circuit so that it can be displayed on the 7 segment display. It's a tranceiver and demodulator essentially.

I need to know if the digital signal from the RFM70 can be sent to the LM8560 via a certain pin to display on a 7-segment display or if there are any other alternative modules or circuits that may be used to perform this.

The reason the NPL signal is broadcast on 60kHz is because, unlike 2.4GHz, 60kHz carries far beyond line-of-sight.

Sorry, I have a bad habit of modifying my original replies several times. I won't update it again but please re-read it.

2.4GHz signals don't travel far, only a few tens of meters, maybe a kilometer with special antenna and clear line of sight. Not sure how you get a time signal via that. Can you post a link?

Those two posts are very helpful. Thanks. I've looked at alternative modules that support MSF 60kHz frequency and I've found the MCM-RS232 module which i'll be having a deeper look into.

Another part of the project is to be able to call a person via a cellular line (or if possible Skype - which may involve a hell of a lot more work) I'm guessing i'll be able to use a similar transceiver that operates in the 872-960MHz cellular band such as the SiFLEX02-HP transceiver module (although that may not fit in a 3x3inch wristwatch. Are there any important factors to cellular contact that i may need to consider such as having an active SIM card module, any limitations to sending signals to phone company antennae. Is the Skype contact idea plausible without extensive programming skills?

Really appreciate this help and once again, thanks :).

Yikes! This is advanced stuff for a first Arduino project. My advice would be to keep it simple for now. Just the 60KHz time signal receiver, the Arduino and a 4 digit led display. Once you have that working, then build on that.

I wish my lecturer felt the same way... She was the one that recommended I do this for my final year project. At least no one can blame me for struggling and asking for help haha.
For the receiving part, at least, i'm only really struggling with understanding how the signal is sent from NPL (their site isn't incredibly helpful i find) like is the time, for example 00:00am, sent as a string of radio frequencies which is received by the arduino and then converted to binary e.g. 00000000 which can then be manipulated to display 00:00am on a 7-segment display?

If i'm asking too many questions then i'll leave you guys alone, you've been a great help already.

Google "npl time signal protocol"

Azaxa:
The RFM70 is receiving the wireless signal from NPL (or a similar company) that gives us the time/date and is converting the radio frequency signals from NPL to a digital binary signal which is then to be sent to another circuit so that it can be displayed on the 7 segment display. It's a tranceiver and demodulator essentially.

What's the purpose of the 2.4GHz link? Why don't you have the unit with the 7 segment display receive he 60kHz signal directly?

The radio signal from NPL has patterns in it at about the right speed for a hobbyist watching an LED to see something every second and for an arduino project to decode the broadcast every minute of hh:mm:ss and a few other things and then synch an arduino digital out pin to the start of every second. It is way off what can go through a 2.4GHz transceiver, as those contain blocking capacitors which don't pass anything slower than a MHz.

Try looking up "Nixie Clock" as parts for those get sold from the same place as a little radio component which I think you'll want.
I'd avoid the 2.4GHz work altogether if this is your first project, as those don't like untidy hand cut transmission lines and even 5mm of unshielded cable looks like an unwanted antenna in the GHz.

Have rethink about what you want t accomplish with the transciever as that might be a lot of heartache compared to wiring a room with a 5V TTL level synched to the tick of the NPL atomic clock.