Electrical – NFC Reader based project with microcontroller

When using high-side N-channel MOSFETs, a MOSFET driver chip is generally used (e.g., an IR2130). These chips require a boost capacitor which allows the gates of the high-side MOSFETs to be driven with the required voltage. The downside of this is that the MOSFET driver has a restricted operating range (typically 10V-20V). The second down-side is that you can't drive the MOSFETS to 100% pulse-width; this is usually not a problem. Alternatively you could use P-channel high-side MOSFETs and N-channel for the low-side. With this configuration, you can PWM the low-side switches only and save some power. (You can do this with all N-channels as well, it's just trickier since you have to keep the boost capacitors charged). Go to Digikey and search for "mosfet driver", you'll want the 3-phase bridge drivers specified for external switches.

As for the MOSFETs themselves, I don't recommend you use them in parallel. This would increase your footprint as well as your gate charge. Instead, look for high-current mosfets on Digikey. My favorite packages for these are D-Pak, 8-PowerVDFN, and PowerPAK 1212-8.

Atmel has an app note for sensor-based and sensor-less motor control. Unfortunately AVRs don't have much processing power and your control algorithm will likely be restricted to fixed-point math because of this. Because of the processing power limitations, you may want to consider not using the Arduino environment and instead use straight C or assembly.

You may have some trouble isolating the I2C bus optically since it's a bi-directional bus. If you were to use a communication system with single direction lines, you may want to look at TI's line of isolator chips (e.g., the ISO7221).

RFID certainly is cheaper and simpler.

The main difference between the two is that with RFID the person carries a card/tag/etc. that can be thought as "passive". It is only powered when near (and by) the receiving antenna. NFC is to be embedded in cellphones and uses its source of power (the battery).

RFID is pretty secure for most applications. It is widely used around the world for bus fares. Only when you have applications that require more security (credit/debit card transactions, for instance, in which the average transaction amount is significantly higher) it wouldn't be recommended. Thus enters NFC.

For a test/demo environment, I'd recommend you to visit SparkFun or Adafruit. Their products are aimed at the hobby market, so they are pretty easy to start using. In general they'll open a virtual serial port via USB, so what you'll need in PHP is just any standard library for sending/receiving data through a serial port.