[TriEmbed] TriEmbed Digest, Vol 7, Issue 21

John Vaughters jvaughters04 at yahoo.com
Fri Jan 3 16:23:04 CST 2014


Chip,



Thanks for sharing and I can see you have put in alot of effort on this project. I love the pcb effort.

Nice Work!!!


> - More power optimization - can I tell the clock to sleep as well?  batch writing to the SD card?  John, I will be interested in your thoughts about the M41T62LC6F clock.

This clock looks like a great chip. It says it can work down to 1V that might save power, but to get the 1V might waste more power than you save. Probably just run it at 3.3v. It seems low power already. There is not really a way to sleep the clock function itself, it has to run. But you would want to disable the Sq, wave output. Also, if the I2C is not talking that will save power and since the processor will be sleeping, you will probably be in best power saving mode when the processor is sleeping. I do not think you can do much more than that.

>- Feedback from beta testers - perhaps a MAC/PC based way to set the clock

The best way to set a clock is just have a routine on the Arduino that accepts a command from the serial interface to your PC and create a script or program to communicate with the Arduino. I usually do this by using the PC system time that is sync'd with internet time clocks and converts it to a string that your Arduino can understand and set the clock via I2C. If you have enough code space it would be great to be built in with the Trail Counter, but you can also just have a small program to set the clock and then transfer over the Trail Counting program after it is set. 

>- Start designing a complete circuit board integrating the breakouts.  Need to either learn surface mount or find a cheap low-volume contract manufacturer.

I know a low volume manufacturer right here In Raleigh, but I am not sure they are what you need. They may still be more expensive than some other low volume houses you can find on the internet. Let me know if you are interested. I can get you a contact. 


Also on the I2C distance, that really depends on these factors. 

1. Pull up resistors
2. Chip voltage thresholds for communication
3. Chip communication speeds
4. Environmental aspects that may cause line noise

This is always a trial and error type situation. You may want to come up with some standard lengths as options. I think you should be able to get several feet without a problem, but you really need to test it. On the pull up resistors you will probably want to tune this to match the lengths of your wire. You should be able to change the pull up resistors to optimize your power usage and consider using the slow side of your transmission rates on your chips. This will allow you to increase you distance as well as decrease your power usage by choosing the correct pull up resistors. I think even the slow transmission rates should be fine for your application. Be sure to use twisted pair wire to fight against line noise. If noise becomes an issue some ferrite beads might help solve that issue. You should be able to find some info on the web on tuning your pull up resistors.

John Vaughters
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