I understand that the Bluegigga WT12 requires RS232 when using UART which is what I'm planning to do and thus it requires high voltages? Would that make it unsuitable for a battery powered application? If not what alternative Bluetooth module could I use that supports SPP and has a robust API like iWrap?

  • 1
    \$\begingroup\$ What's a "WT12"? \$\endgroup\$
    – brhans
    Jul 18 '17 at 19:35
  • \$\begingroup\$ You should provide links to datasheets for any devices you mention in your question. \$\endgroup\$
    – Transistor
    Jul 18 '17 at 20:56
  • \$\begingroup\$ My bad. Edited that in. \$\endgroup\$
    – E Skal
    Jul 18 '17 at 21:58
  • \$\begingroup\$ The UART interface is CMOS levels, you can connect it directly to your micro-controller on board. No rs232 hw needed. \$\endgroup\$
    – sstobbe
    Jul 19 '17 at 1:25
  • \$\begingroup\$ I see. I tried hooking it up to an Arduino before, nothing thus I was curious. \$\endgroup\$
    – E Skal
    Jul 19 '17 at 15:57

One would first have to ask "how big is your battery? (Capacity)". However, use of RS232, which does use higher voltage than logic circuits, does not preclude battery operation.

These devices use chips such as the MAX232, which generates RS232 voltages levels from 5V using charge pumps.

Edit: I think I see why you're confused. The datasheet includes the following:

WT12 Universal Asynchronous Receiver Transmitter (UART) interface provides a simple mechanism for communicating with other serial devices using the RS232 standard. The UART interface of WT12 uses voltage levels of 0 to Vdd and thus external transceiver IC is required to meet the voltage level specifications of UART.

This really badly worded, in my opinion. The WT12 does not use RS232 levels. It instead uses logic levels. What it is trying to say is that to connect to an external PC using RS232, it requires an external transceiver, such as the MAX232. Its UART pins can be connected directly to the UART pins of almost any microcontroller which uses the same I/O voltages: if you're powering the WT12 Vcc on 3.3 volts, use a microcontroller also with 3.3 volt Vcc (or Vio if that can be set separately).

  • \$\begingroup\$ Is there a need to use the MAX232 if the Micro controller is operating at the output of the Bluegigga WT12? It seems redundant. \$\endgroup\$
    – E Skal
    Jul 18 '17 at 22:00
  • \$\begingroup\$ Thank you, that makes sense. Any micro controller that has internal pull ups right? \$\endgroup\$
    – E Skal
    Jul 20 '17 at 15:58
  • \$\begingroup\$ Internal pull-ups has nothing to do with it. Look at table 4 of your datasheet. It shows that I/O pins can tolerate voltage as high as Vcc+0.4V. So if you power the module from 3.3V, it cannot accept voltage higher than 3.7V. If you have a microprocessor who's I/Os output 5V because it's powered by 5V, you cannot directly connect them. Also, it that case, a logic high output from the WT12 might not me high enough to be reliably recognized by the micro. These problems also occur in the opposite direction with a lower-voltage micro. Just match the voltage levels to be safe. \$\endgroup\$
    – DoxyLover
    Jul 20 '17 at 16:39
  • \$\begingroup\$ My bad I read that : If UART is not disabled, a pull-up resistor has to be connected to UART_RX. as needing a pull up to functions but that's only in the case for not using UART at all. Again thanks for the help. \$\endgroup\$
    – E Skal
    Jul 20 '17 at 20:11

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