i'm trying to implement an application using a Bluetooth 4.0 module, and I wonder if using this application with an Iphone 3GS containing a simple Bluetooth 2.1 EDR module is going to enable me take advantage of the the low energy in my 4.0 module. Thank you for your answers
Bluetooth 4.0 is the standard, which includes both classical Bluetooth Basic Rate/Enhanced Data Rate (BR/EDR) and Bluetooth Low Energy (BLE, or Bluetooth Smart, which is a marketing name).
Compatibility depends on the the device and Bluetooth chip e.g. is it a BR/EDR only chip (Bluetooth 3.0), a BLE only chip or a dual-mode chip capable of both BR/EDR and BLE. A dual-mode chip can (until 4.1, at least) only operates in either BR/EDR or BLE mode for any given connection.
A dual mode chip, certified as Bluetooth 4.0, can and should be able to connect to a Bluetooth 2.1 chip, in BR/EDR mode.
A Bluetooth BLE (Bluetooth Smart) chip will not be able to.
First, you must clearly determine if your Bluetooth 4.0 module is only capable of BLE.