after some days with 0 replys in the software forum I wander if my questins are too stupid or I´m not on the right place so I try it here, regarding that I´m not loking for the made code but just for some directions. thanks to the "childrens software" from eduware (http://dimeb.informatik.uni-bremen.de/eduwear/?cat=4) and dispyte of being "from mechanics" I´ve made on first day I´ve seen an arduino some realy working programs, and now I´ve started digging on C, but the questions... -Can the arduino work with a car batery? -Can be stored counts of 2 whells at diferent rpm´s on the eeprom and just before it get full send them by sms and clear the eeprom (I have a diecimila with a gprs module from libelium). I intend to count 1 minute for every hour and compare rpm´s. Thanks in advance for any reply and sorry the english from portugal.
For the battery thing, my guess is that you have to really take care about the power regulation.If I recall right, there's a huge spike of current at startup, and that might fry your arduino. + you'll have to convert the 12v into something more suitable like 9V, but that isn't too hard. My bet is that you should use the lines going to the battery adapter inside the "cockpit" (don't have the english name). Not sure but I think those lines are already protected from spikes.
The arduino eeprom is quite small (512 byte) so you can only count a limited amount of time. I don't know at how much RPM a car wheel can go, but if you need to have a large storage capacity, I'll advise you to dump your content to an SD card. This way, you'll even be able to get the files on your computer and trace nice curves and stuff.
Don't know about the sms stuff, though
You can run an Arduino in a car situation - one thing to watchout for is that the voltage isn't 12V. When the engine is running, the alternator charges the battery with typically 13.6V and it may exceed 14V.
That said, a decent regulator on a decent heatsink bringing the voltage down to 7V or so before supplying the Arduino will work.
Have you decided how you will send the sms? I ask as I'd like to be able to do that myself, and wonder what you have come up with.
We’ve been through the car voltage thing before - the arduinos with a 7805 regulator (serial, NG, and I’m pretty sure the Diecimilla) can handle automotive voltages. The 78xx family are typically rated up to 36V input (depending on manufacturer, YMMV).
You may need to watch for heat problems around the regulator, especially since automotive applications tend to be quite hot.
Sorry to every one for the lack of details, but what I pretend to do is an anemometer for a wind turbine whitch I´m building a working prototype, now I need to realize the relation for the rpm on the anemometer and the rpm on the rotor to build the generator with more or less working bobines so I can vary the charge on start, aceleration or deaceleration. The car batery is stand alone and only for a matter of working time. For the SMS I´ve a GPRS module for arduino from libelium ( http://www.libelium.com/tienda/catalog/product_info.php?cPath=21&products_id=59 ) With this beter explanation can anyone give directions? I think I´ll folow the advive of SD card, because I expect at least a working week ( counting five minutes every hour ) and I dont want to send one SMS´s for hour whit two nunbers on it, but only when it´s full, whitch I believe is 160 characters. Can I make two variables for related countings in a lake of time?