Increase sample duration

[Jay Lash]

I started looking at increasing the sample duration so I can record my
entire 11-day trek next summer. Before I got too far into looking at
the number of time scales, samples, graphs etc I checked the data
sheet and did some calculations. Turns out I dont have a prayer for
getting what I really want:

* ATmega328P has 1K byte EEPROM.

* I need 15 days to be able to record my full trek and get back to a
computer for download before I start overwriting.

* I think 4 samples per hour are a bare minimum and would really
prefer 6-8.

This gives 4 * 24 * 15 = 1440 samples at 8 bits per sample is 1440
bytes for just the temperature data.

So...I got to wondering about adding a I2C EEPROM (like:
https://www.sparkfun.com/products/525). Looks like the firmware
would need a little change so the I2C slave address is passed for each
read/write rather than set once during init. Doesnt seem to be any
BMP085 access during the interrupts so all I2C access should be from
main() and therefore safe for accessing multiple devices. Any thing
off hand from a software standpoint that would prevent this working or
would cause problems?

Hardware wise I was thinking about simply "dead bug"ging it in for my
own use. If it works you could sure add it to the board if you
wanted.

Thoughts? Alternatives?

[Steve Chamberlin]

The first version of the Logger Mini actually had an external I2C 128KB EEPROM for exactly that purpose. I never wrote software to make use of it though, and it was deleted from later revisions of the board. The part I used was http://search.digikey.com/us/en/products/M24M01-RMN6TP/497-6351-6-ND/1827939?wt.z_cid=ref_octopart_dkc_buynow

You can see the EEPROM just below the ISP programming header in this photo: http://www.bigmessowires.com/lm_back.jpg

Another option might be to use an SPI EEPROM, then you could design a carrier board that plugs into the ISP header, which already carries all the signals you'd need.

Steve

[Jay Lash]

I like the SPI idea because it could be a simple daughter board. But
I dont know how you would extract the data via blsync. Maybe you'd
have a pass-through on the daughter board with a switch (pair of
buffers with enable lines) so the micro could read a big chunk of data
into sram, throw the switch and transfer it to the PC then repeat.

On Dec 19, 1:39 pm, Steve Chamberlin <steve.chamber...@gmail.com>
wrote:
> The first version of the Logger Mini actually had an external I2C 128KB EEPROM for exactly that purpose. I never wrote software to make use of it though, and it was deleted from later revisions of the board. The part I used washttp://search.digikey.com/us/en/products/M24M01-RMN6TP/497-6351-6-ND/...

[Steve Chamberlin]

Good point, I didn't think about the data download half of the question. I guess a pass-through would work. Or maybe you'd find it easier to tweak the logger PCB layout and make a new one with the extra EEPROM on-board?

[Jay Lash]

So I got a sample of the I2C EEPROM that you originally had in the
design. And, I found that my unit is one of the original circuit
boards with the EEPROM in the design (we both would have realized this
if we had stopped to think about it). Now to get the part installed
and make the time to work out the firmware udpates.






On Dec 19 2011, 7:53 pm, Steve Chamberlin <steve.chamber...@gmail.com>

[Steve Chamberlin]

Sounds good. It hopefully shouldn't be difficult to modify the code to use the external EEPROM instead of the built-in EEPROM memory. Let us know how it goes!