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I have a Funduino joystick shield and it features a 4 pin bluetooth socket in the top right hand corner (just above the D, T, - and + legends).

Joystick Shield

For some reason, on eBay, 6 pin bluetooth modules are cheaper and more common than 4 pin bluetooth modules.

Bluetooth Module

The joystick shield's 4 pin socket is labelled R T - +. Obviously these correspond with RXD, TXD, GND and VCC on the bluetooth module.

I was wondering:

  1. What is the difference between the 4 pin and 6 pin modules?
  2. Can I use a 6 pin module in the four pin socket on the joystick shield?
  3. What is the function of additional STATE and EN pins on the bluetooth module?
  4. Are these two additional pins necessary as other modules do not have them?
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  1. What is the difference between the 4 pin and 6 pin modules?

The 6-pin modules have more pins, used for other features.

  1. Can I use a 6 pin module in the four pin socket on the joystick shield?

I don't see why not, as long as you tie/float the other pins appropriately.

  1. What is the function of additional STATE and EN pins on the bluetooth module?

Whatever the documentation says they do.

  1. Are these two additional pins necessary as other modules do not have them?

Probably not. But they provide additional functionality.

  • Thanks for the confirmation. Butchering a 6 pin module down to 4 pins certainly seems to be the cheaper option. – Greenonline Jul 31 '15 at 0:11
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    Just poked around, and EN is connected to the voltage regulator; pulling it low will shut down the whole module. No idea what STATE does though, since it connects to a GPIO. – Ignacio Vazquez-Abrams Jul 31 '15 at 0:13
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After some more concerted searching I have found the answer on Success Using the JY-MCU (linvor) Bluetooth Module:

The module has 6 pins labeled on the back, but most modules only have 4 of those populated with pogo pins. KEY & STATE seem to be not required, as KEY is used for flashing the device and STATE simply indicates if the device is awake or not. So that leaves only GND, VCC, TXD, RXD. Not shown is Pin 11 which is the RESET pin, resetting the module when pulled LOW.

So, the answer is apparently yes, and you can buy a cheaper 6 pin module and remove (snip/desolder) the two additional pins. The EN pin is also apparently labelled as KEY on some modules.

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