Yo usé siempre estas memorias escribiendo y leyendo de a un solo Byte, usando solamente I2C_eeprom_write_byte, I2C_eeprom_read_byte.

El tema principal es que tienes que descomponer (y luego rearmar) tu valor long en 4 bytes, y esos enviárlos (y luego recuperarlos) de la EEPROM.

Acá hay algunas soluciones: http://arduino.cc/forum/index.php?topic=50658.0

Con esto resuelto debería ser simple el almacenaje y la lectura, que tendrías que hecerlo cuatro veces (una por cada Byte).

Espero esto te ayude.

Reading this article http://www.embeddedsys.com/subpages/resources/images/documents/microsys_art_RS485.pdf it states that:

Without a common ground, the circuit may work, but the energy from the imbalance has to go somewhere and may dissipate as electromagnetic radiation.

I've made 485 circuits without a common ground, and they worked anyway. I've grounded just one end and it worked transmitting shiftout data at 60meters without problems. Maybe I was just lucky

Todo depende del tipo de golpe que quieras medir.

Resistors looks like these:
One is brown, yellow, black, black, brown (140 ohm)
Other is orange, black, black, black, brown (300 ohm)


They are not big.

Thanks fungus. In most of the cases a pair of leds dies, and the other 3 survive.
Zapro: I wasn't even aware piranha was a brand 
You are right, I was a victim of "EL CHEAPO" Leds Made in China.
Problem is....everything I can buy arround here are from the same origin.

[brick]

Pardon my awful description that led to misunderstandings.

The led modules look like a brick of plastic, where the leds and resistors are placed, and all is covered with more melted plastic. You can see inside the plastic some conventional THT resistors. All this info was in the effort to describe the product. Here is a better picture of some similar modules that have only 3 leds:

The modules look ok from the outside, though the leds are no longer bright enough and some of them do no longer work.

12V come directly from a commercial switching power source with 2.5 amps capacity (Can this be blamed?). Each led module consumes 40mA, and I have 42 modules.

Thanks for your help guys. looks like I shoudn't have trusted the dealer who said that these where 12V modules, and lower it a little bit. I'll try dimming with PWM on the high side.

This modules include the resistors inside (you can see them inside the melted plastic brick).

The circuit is easy:
- led module anode to +12V
- led module cathode to one of the ULN2003 darlingtons, that switches the path to ground.

Thats it, no added resistors.

First experiment will add PWM to the +12V, because adding resistors would be a pain.

I've used some generic blue led modules to build a big clock with 7 segment displays.
This modules have 5 piranha leds and resistors in a weatherproof enclosure (a brick of molten plastic).
Modules look like this:

They are rated for 12V, and a real datasheet is not available.

After a year and a half of constant use, I've noticed that some of the leds are burnt, and most are not as bright as the new ones.

Modules are wired to 12V, switched with darlingtons in a ULN2003.

The display uses a sheet of white hight impact polyestyrene as a diffuser, and I've noticed that it turned light yellow where the led light it.

So my first suspicion is that the modules are dissipating heat, and this is shorting their life. Or is it the UV light that yellowed the plastic?

Modules are not warm to the touch. And there is no sign of heat on the MDF piece they are glued with hot glue. The sign is place inside, and summer temperatures can go up to 32 degrees celcius.

Does anyone have experience with this kind of modules an their expected life? Would SMD LED strips last longer?

If you want reading distance, you'll have to forget about regular 125kHz cards or 13.56MHz RFID Tags. You'll need UHF or special long range tags.
UHF readers are also capable of reading multiple tags at one time, but you just want to read once in every location.
You can use just one reader, an antenna multiplexer (like this http://www.impinj.com/Speedway_Reader_Antenna_Hub.aspx) and as many antennas as spots. But we are talking about +2000 dollars. I don't think an Arduino will be able to handle the communication with the reader either, you might need a PC.

Since Battery discharge is not proportional, you don't need the whole spectrum of the 9V mapped into the 5V of the analog input.
You can use zener diodes (one or more) to lower the voltage like shown in this circuit:


In the example, the two 5V zeners in series lower the input in 10V, so you have a better resolution of the remaining voltage, that is significative for measuring the charge. I did use this circuit, because a 12V battery is dead when it reaches 10V, no need to measure under this voltage.

So lets say you'll consider a 9V battery dead when it reaches 7.5V, you just need to measure with big precision this 1.5v. So If you use a zener of 4.3V, you have
an arduino ready signal and wont be misusing so many steps of the ADC.
This way you'll get more precision when reading the battery charge.
Hope this helps.

If you are using just ON/OFF switches/sensors, you don''t need analogue inputs, use the digital ones. Just make sure you are using the right pull up or down configuration.

I've used some cheap float switches from ebay, and they worked fine.

Con PWM y un transistor? Yo empezaría probando por ahí.

Soy un hobbysta empedernido, y me compré este equipo.
La verdad es que me resultó fácil de usar y suficiente para el uso que le doy.

[Any ideas?]

I built the circuit from my last post (Or you can find here http://320volt.com/12v-ve-5v-600ma-irf9530-mosfetli-akim-sinirlama-devresi/). Worked like a Charm. Added a couple of LEDs to monitor if it was in normal mode or in overcurrent protection (One at the Gate and one at the Drain of T2, plus 1K resistors in series).

I understad the basic working principle of this circuit: when the voltage drop in R1 is bigger tha 0.7V, T1 starts sto conduct and shuts T2 off. Thats the easy part.

What I do not get is the role of the two capacitors. Any ideas?

C1 is quite big, and and of the drawbacks of this solutions is that it has quite a big charge after plugging it off from the power source.

I've used ULN2003 to work with 12V led strips. It's a darlington array that will sink current from the strips, activated with an Arduino's signal.