miniLOG - Standalone Data Logger

[dannyf]

It still uses 15mA

Not sure what "it" is. Posting a schematic / measurement point would be helpful.

What were you expecting?

[fenclu]

If it doesn't increase the size of the board, I'd pick an SD card slot. Those with MicroSD cards can use a dirt cheap adapter, and that way, both types of card work. Alternatively, just log to an eeprom and output the data over the serial interface?

If you're going to use EEPROM, you might as well use something cooler (but a bit more expensive) like FeRAM.

For example, you could use this: http://uk.farnell.com/ramtron/fm33256b-g/fram-mpu-support-256k-14soic/dp/2103831

Datasheet here: http://www.cypress.com/?docID=42548

It's a 256 kbit feram with real time clock, alarm , event counter, works with 2.7-3.6v, 100 trillion writes, the works. Save money on separate rtc chip, lower power consumption because it uses less power than eeproms and it's fast (almost instant) etc etc.

I actually settled for an SD card a long time ago. Thanks though, that's something to consider.

Not sure what "it" is. Posting a schematic / measurement point would be helpful.

What were you expecting?

I meant the entire circuit is drawing 15mA from the battery (it's about 23mW). I was expecting something below 10mW. I mean come on, there only an Atmega chip, barely powered MCP3201 (not even talking to the microcontroller) and a 74HC595 shift register for multiplexing LEDs (all LEDs are off). That's even without the SD card.

Here's the latest schematic http://1drv.ms/1mnuZAe

[dannyf]

The avr, depending on the frequencies it is running at, may consume 10ma all by itself. so 15ma isn't out of this world.

For low current consumption, think about putting the mcu to sleep in between sampling or to run at different speeds.

Power consumption is more of a software thing than a hardware thing.

[fenclu]

Do you think it might have something to do with the fact that I'm running it with an Arduino bootloader and 16MHz crystal?

[dannyf]

With 16Mhz crystal, you are likely in the 10ma+ range and 15ma is reasonable.

Slow it down: current consumption is almost proportional to speed.

[fenclu]

I'll try to underclock the MCU by modyfying the Arduino bootloder. 1MHz oughta do it for SPI controlled ADC and SD card?

[dannyf]

Depending on your current budget. 1Mhz will get you to about 1ma (on the avr).

If your avr idles a lot - typical for a logger, you really should think about putting it to sleep: the current consumption there is in terms of ua / na vs. ma in the run state.

[fenclu]

I found this Arduino library: https://code.google.com/p/narcoleptic/

I'll try and use it, should my 30kB flash memory allow it.

[dannyf]

I am partial to the arduino bootloader: I blow it out every time,

Arduino boards are great in terms of their availability and low prices (for the clones). I buy them and then program then via icsp.

[fenclu]

It's really more about the environment. Yes, I'm lame and can't program in real C...

[fenclu]

I published my project at Hackaday Projects as a beta tester: http://projects.hackaday.com/project/194-miniLOG---Standalone-Data-Logger

I probably need to mention why I'm actually doing this project. I'm a high school student and a beginner. This project is supposed to help me pay for a basic lab. I don't have a scope, a logic analyzer or even a decent multimeter, that's why it's a big challenge for me. I need some way to get the money, I was even thinking about a small Indiegogo campaign to get small funds for a basic lab, as some guy did before.

[linux-works]

I like the idea of data loggers.

being a networking person, I would like to have wireless data streaming.  sd cards can fail (and fail horribly!).  there goes your data.

otoh, if you use wireless (of some kind, lots of choices here) then you can upload data from many sensors to one host (a linux host would be my pref, of course) and that can save data to raid disks for reliability.  in fact, if you multicast (xbees can do that for free, btw; if they are all tuned to the same channel, one transmits and they all see the same data coming in to them) then you can have nearly free reliability via redundancy.  xbees also travel pretty far and they do offer encryption, if that matters.

there are cheap digital radio modules, too.

there is IR if you have line-of-sight and only need to send data one-way.  I would checksum the packets and sequence number them (like tcp) for reliability.

having a local cache of data is fine; but I'd want to get the data off the sensors and onto something reliable.  for times where the remote upload host is not reachable, you buffer the data locally and keep trying to connect to the upload host and when you do, you flush the buffers.

[fenclu]

That's partly the reason why I put the UART connector on the board. If only there is some memory left on the microcontroller it should be possible to hack it to use bluetooth or Xbee module. Not really my piece of cake so I'll left it to the user/community.

[fenclu]

Crap...I'm now running the board at 4MHz and the power consumption. I'm out of ideas. Obviously I need to put the MCU to sleep, maybe increase the values of LED resistors. I'm just curious, why slowing the processor down 4 times didn't make any difference?