Need Advice - DIY Sea Turtle Nest Temperature Logger

Thanks for all the support guys. I really appreciate the contribution y'all are making by at least with regards to brainstorming.

Great concept Tim, but it might be a little bit more advance to what I would like to accomplish.

With direct response to Michael, I do have some experience with breadboarding and soldering. So that in itself wouldn't be an issue. I've never really had a hand in coding, but I do have some potential resources around me that might be willing to help out.

I'm still working out the kinks to the whole project design, but my projected budget that the university is willing to provide is US$500. That severely limits my options, but I am willing to personally contribute to this research to ensure it gets completed. If I could get 50 data loggers at US$10 a pop, I would be ecstatic. Realistically, I'm thinking that 20-25 data loggers will suffice, and I will have to utilise each data logger twice to get a decent enough sample size.

The film canisters are a great idea, as I don't want to disrupt the sea turtle nest in itself while collecting these measurements.

vsluiter:

From what I understand, most of these devices use a coin cell battery, which should be able to power the device at least 6 months, using 1 minute intervals. I would be collecting these measurements at 1-4 hour intervals; it hasn't been decided yet. This is in turn would increase the length of the battery life.

The temperature collected would be around 28-30 degrees C, which is 82-86 degrees F.

Here are some component ideas:

Temperature sensor: TI TMP112AIDRLT (Farnell 1735574 @ £1.41) - 10uA active, 1uA shutdown, 0.0525C resolution, typical accuracy 0.1C worst case 0.5C.

Micro: LPC811M001 (Farnell 2320693 @ £0.56), ARM M0, 16 pin, low power modes, cheap

Real time clock: Microchip MCP7940N (Farnell 2361116 @ £0.49)

EEPROM: Microchip 24AA128 (Farnell 1331285 @ £0.43)

Battery: CR2450, about £1.50 (don't buy junk)

Battery holder, about £0.25.

Each time the recorder wakes up to measure it must be on for about 100mS to measure temperature and will use max 2mA, then write to EEPROM for 5mS using 5mA = 0.225mAS.

If it does once per minute the average current drain is 3.75uA.

Allow the RTC to use 2uA (way more than spec) gives an average current drain of 5.75uA

The battery is good for about 500mAH (depends on which you get) so the battery will do 86,000 hours.

You might be tempted to use a smaller battery but aim for 10x the calculated capacity - you really don't want to run flat for the sake of 25p.

You can get the data out of the uP by a uart interface using one of those FTDI logic level uart to USB cable thingies which work with almost any Windows PC.

By the time you get the pcb, crystal etc I reckon the total materials cost will be about £9, about $15.

Sounds such fun I quite fancy making one myself but I'd better get on with some real work

MK

Nice breakdown!

Since they've got such good documentation I'm advocating the use of the Zero Gecko with internal RTC (EFM32ZG108F160.9 μA @ 3 V Deep Sleep Mode, including RTC with 32.768 kHz) and replacing EEPROM by FRAM. But of course that's personal favourism and some overoptimization, Michaels setup seems very good too.

The Gecko has the RTC on chip so would save the external RTC and so the BOM would reduce a bit - which is good. I picked the NXP LPC800 part because it's in an easy to solder package (and I didn't know about the Geckos - never used them).

I think the Gecko is a better choice than the NXP part if the package is OK - I don't mind QFNs but I know that some hand solderers can't manage them.

I chose the EEPROM because I wanted everything to work down to 2V (you can't trust coin cells to give you any more over their life and a reasonable temperature range) - have you a part number for a FRAM ?

MK

Yes, you can look at this Ramtron part http://nl.farnell.com/ramtron/fm25640b-g/fram-64k-spi-8soic/dp/2077754 or at Cypress's parts : http://www.cypress.com/?mpn=FM25V01-G . I see now that they are waaay more expensive though , and thus mot particularly suited to your project.

There's some background info here too: http://www.ti.com/lsds/ti/microcontroller/16-bit_msp430/fram/overview.page?DCMP=FRAM&HQS=FRAM. The low power properties are especially useful if (re-)writing large chunks of data, which you are not going to do. TI makes the MSP430 (low power micro) also with internal FRAM, but I don't know if it would suffice for your purpose. This one has 16kByte storage (used for both data and program): http://nl.farnell.com/texas-instruments/msp430fr5728irget/ic-mcu-16bit-msp430-24vqfn/dp/2072183 . The interesting thing is that you have a low power microocontroller with nonvolatile storage and an RTC in one package. Still more expensive than Michaels options, but you'll have to place only one part....

Yes, you can look at this Ramtron part http://nl.farnell.com/ramtron/fm25640b-g/fram-64k-spi-8soic/dp/2077754 or at Cypress's parts : http://www.cypress.com/?mpn=FM25V01-G . I see now that they are waaay more expensive though , and thus mot particularly suited to your project.

There's some background info here too: http://www.ti.com/lsds/ti/microcontroller/16-bit_msp430/fram/overview.page?DCMP=FRAM&HQS=FRAM. The low power properties are especially useful if (re-)writing large chunks of data, which you are not going to do. TI makes the MSP430 (low power micro) also with internal FRAM, but I don't know if it would suffice for your purpose. This one has 16kByte storage (used for both data and program): http://nl.farnell.com/texas-instruments/msp430fr5728irget/ic-mcu-16bit-msp430-24vqfn/dp/2072183 . The interesting thing is that you have a low power microocontroller with nonvolatile storage and an RTC in one package. Still more expensive than Michaels options, but you'll have to place only one part....