Hello!
Several MB is small, but it depends on what you are logging. I made a brain wave data logger
which was sent last year to the international space station and which is about 200 km over our
heads every 90 minutes. As there is not so much power over there (Li-ion batteries are forbidden
and therefore one must rely on "dry" batteries), consumption is a key point.
Well, taking back your argument of multiple EEPROMS.
If you want to equal a 4MB AT 45 with 24C512 (64 kBytes), then you need 64 memories. As the hardware
address is 3 bits (A0, A1, A2), then you need to multiplex you I2C bus. Multiplexing a 2-line bus for 8
I/O (both directions) is not trivial. Furthermore, having 64 chip on a board makes it expensive. I think
we can agree with that.
Now for SD card, you have to initialize it every time you power it (this takes power), and writing
is card-dependent, but my experience tells me it may be up to 50 mA. A lot too much for many applications.
I do a lot of bio signals and this does not require high sampling frequencies (about 100 Hz for brain,
max 1000 Hz for heart, less for other parameters). So todays multi mega flash chip are usually more than
enough in many cases.
Now if you really need an SD card, it means that you really need a lot of space. Therefore you will likely
be writing continuously and therefore need more than 1000 mAh per day to power your circuit.
That said, judging from the original post, usually you don't store 100 characters strings, but just the
strict minimum. If you record 12-bit data, then you should fit them in 2 data for 3 bytes and so on.
I know that recently, technology allows to log everything, but the bad thing about it is that people
don't think anymore about what is mandatory and what is not.
What is price of that flash chips ? And can you explain me why is there lots of devices with SD card logging technique.
Why? Precisely because SD card are cheap and developer don't think anymore
But SD card (even micro) are big in some cases. A flash chip (AT45 is 5 x 6 mm), so you can use a smaller
PCB. Smaller PCB is less expensive, etc...
Dora.