You can definitely transmit data using just TX & GND.
Firstly, you want to hook up the ATtiny85 TX line to the FTDI RX line (yellow on the TTL-232R). Make sure that the USB adapter can handle 5V - I'm fairly sure even the 3.3V TTL-232R is 5V tolerant.
According to the example page for SoftwareSerial, you need to set the direction of the TX & RX lines in your setup function:
// include the SoftwareSerial library so you can use its functions:
#include <SoftwareSerial.h>
#define rxPin 2
#define txPin 3
#define ledPin 13
// set up a new serial port
SoftwareSerial mySerial = SoftwareSerial(rxPin, txPin);
byte pinState = 0;
void setup() {
// define pin modes for tx, rx, led pins:
pinMode(rxPin, INPUT);
pinMode(txPin, OUTPUT);
pinMode(ledPin, OUTPUT);
// set the data rate for the SoftwareSerial port
mySerial.begin(9600);
}
The baudrate will be 4800 in your case. The SoftwareSerial library doesn't seem to support CTS & RTS, so just make sure you aren't using them on the host software.
Check out the reference page for more details, where they talk about some potential timing issues which may be exacerbated if you're running at 1MHz using the internal oscillator on the tiny.
The default baud rate is 9600, 8 bit, no parity no flow control (9600,8,N,1).
The HC-06 works with 3,3V ... You can connect the HC-06-TX (output) direct to PC-RX (TTL) but the PC-TX (TTL) CAN NOT BE DIRECTLY CONNECTED to HC-06-RX (input), due to 5V, then you have to put a level converter. In this case is enought to use a resistive voltage divider.
PC HC-06
RX <-------------- TX
TX --> divider --> RX
Best Answer
The JY-MCU Blue Tooth module contains a trace antenna on the flip side of the board, the zig-zag trace at the bottom left in this photo:
(Image source)
While it is conceivable that a skilled person could scrape out the PCB trace leading to the antenna, and solder in an external antenna of just the right wavelength and impedance to work with the radio frequency input/output stage of the device, the odds of any improvement in performance are little to none.
It is also worth noting that integrated Bluetooth devices such as this one are typically not designed with sufficient power headroom in the RF stage to be able to drive a significantly bigger load than the antenna designed into such a board: After all, if the intent of an external antenna is to increase range, that would necessarily translate into either a highly directional signal, or higher radio frequency power.
It might be a better option to simply choose some other Bluetooth module, one that supports an external antenna out of the box.