cheap battery powered long life wireless data acquisition

I want to do some long term temperature logging with battery powered sensors sending data back to a PC. I'm looking for a very low data rate, for example one measurement per hour from each sensor, and up to a dozen sensors. I'd hope the sensor battery life would be at least several months, because the sensors won't all the easy to get at.

Is it possible with Arduino? Is it possible cheaply?

For temperature sensing, I'm envisaging something like the LM335A, which gives an analogue output signal. I assume I can use an analogue input on the Arduino to do A-to-D conversion.

For data transfer I'm planning to have a receiver permanently running at the PC, and have each each sensor wake up to send a wireless data burst every hour or so. I initially looked at using ZigBee for the data connection but by the time I've bought a shield and the XBee transmitter/receiver for each sensor the costs get prohibitive. Then I saw the laipac transmitter/receiver modules from Cool Components and even showed Arduino code for a simple sender/receiver, and that looked ideal for one-way intermittent data transfer.

Battery life is obviously going to be an issue. I've seen several posts here discussing the watchdog and sleep mode options and the importance of turning off all the peripherals, but one of the threads sent me to http://interface.khm.de/index.php/lab/experiments/sleep_watchdog_battery/ which mentioned that the voltage regulator and USB still consume a considerable current even in sleep mode. So then I looked at the PICO1TR from Wibloc. It looks as if it would do the job but needs DIY assembly and I think that soldering is too fine for me to tackle. Finally I saw the arduCHIP which looks like just what I need, and it sounds as if Mr FM is offering them completely assembled. Since these don't have USB (and nor do I want USB if it's going to ruin the battery life) it seems I'd need something like the TTL-232R USB to TTL Serial Converter Cable from wiblocks to program it.

To receive these data bursts I'd plan to use something like a Uno and power it off the USB.

Finally, a little application on the PC to receive and collect the temperature samples from the Uno. I haven't looked into this side of it at all, but I assume we can transfer data between an application on the PC, and the Arduino.

So, after a couple of hours of rushing round like a kid in a sweet shop, that's the sort of solution I'm thinking about. Does this seem like a sensible approach, or am I barking up the wrong tree?

I'd have a look at Jeenodes, they have built in wireless, are Arduino compatible and IIRC there's a very low power one designed for just this purpose (or maybe they are all low power, can't remember now).

http://jeelabs.net/projects/hardware/wiki/jn6


Rob

Thanks Rob,

They look like a more expensive solution than I'd been planning but a lot less expensive than the shield/XBee approach that I had considered. I do like the idea of a full bidirectional link rather than the simple one-way link I'd been envisaging. I'll need to talk to JeeLabs and find out how much current JeeNodes consume when they're asleep.

I would go with xrf modules, they are cheap at around £18 for a pair and have the same foot print as xbee, they also have very low power sleep settings and you wake and sleep them by setting a pin on the module from your arduino or similar.

I am using a seeduino stalker with a small 3.7v lipo and a small solar panel, the stalker has inputs for both the panel and battery and takes care of the charging you can even interface with the charge circuit to get the current state of the charger and voltages. The stalker also has an xbee socket on board for the xrf so all you have to do is add an extra lead to control the sleep/wake. If it is temperature you are interested in the seeduino stalker also has a tmp102 sensor on the board, there is a RTC as well so you could actually sleep the seeduino as well and wake it up on a timed interupt.

If you dont have any sunlight (indoor etc) I think you could run this board for several weeks on a 6000mah 3.7v lipo. Take a look at proto-pic.co.uk this is where I buy most of my stuff.

Here is the pachube feed for my logger https://pachube.com/feeds/36010

Regards,
Mark

Take a look at NFR2401+ modules, SMS format, realtively low power, Multipipe capability, other features that might be handy, and they are a lot cheaper than Xbees.

One problem you are gonna run into a wall with (depending upon range requirements), is transmit power usage for remote xmitters. That's what is going to chew up your battery life.

Would using a wired (twisted pair) remote sensor to report to a more accessable collector/transmitter be possible? Easier to get to the battery pack and save some expense (only need one sensor collector arduino, instead of one for ech xmitter/sensor).

Unfortunately proto-pic seem to be discontinuing the XRF. :frowning:

I suspect the NFR2401 modules will be overkill for what I need - I'm only going to be moving a few bytes per hour and I won't be too upset if any of it gets lost.

From what I can see so far, the easiest route will be a JeeNode USB and an LM335A. It's far from the cheapest or most powerful solution, but I figure for my first attempt with Arduino I'd best keep things simple.

PeterH:
Unfortunately proto-pic seem to be discontinuing the XRF. :frowning:

Sorry I should have said I get my XRF's from ebay, the uk supplier sells them there, normally quick delivery, you will want to pick up the breakouts as well.

http://www.ebay.co.uk/itm/XRF-wireless-RF-radio-UART-RS232-serial-data-module-XBee-shape-Arduino-PIC-etc-/220881973451?pt=LH_DefaultDomain_3&hash=item336d9770cb

Data sheet here... ciseco.co.uk

Thanks for the tip, markab.

While I was surfing Ebay I found lots of adverts for parts from China. Is everything made over there these days? They're offering NFR2401 radio modules for under two quid and quite a lot of other stuff looks very cheap too. How on earth do they manage to buy the components, assemble it, bulk ship it to the UK and they post it to me, and turn a profit? Post and packing alone would normally cost more than that just within the UK. :~

So the current 'plan', such as it is, is to find a cheap Arduino with low sleep current requirements, and add an NFR2401 for the radio and DS18B20 for the sensor.

I still need to get my head around the 1-wire protocol and make sure these bits aren't going to trip over each other, but it's looking quite promising.

The arduCHIP can also mount an 8MHz resonator and run it off at 3,3V. Just post me if you are interested in this config.
Thank for thinking on the arduCHIP.
If you are also looking for USB connectivity while developing, think on the arduStamp, is similar to the arduCHIP but with USB connectivity. When you are done, you can detach it from the main AVR and use it in another project.

Cheers,

fm