The Engineer Tutor
Learn from our Experience
In my travels through the internet I have stumbled upon these bluetooth serial ports. I have never used them and wondered what they would be good for. I filed that away in my brain for later use. I am now in a situation where I’m unable to take my computer to a customer site. They allow me to have my phone but no computer. I have purchased a bluetooth keyboard for my phone and thought I could hook up a PIC to my phone also if I had a serial bluetooth adapter hooked up to the PIC
I ordered one of the bluetooth serial adapters thinking I could do that. I received it a couple of days ago. I eagerly tore open the anti-static bag that it came in and ripped off the wires of an old project on a bread board and proceeded to wire up the module.
The first thing I noticed was the silk screened letters on the back of the board denoting the function of the 6 pins that it had. I promptly hooked up the RX pin to the transmit pin on the PIC. I cranked up the software hooked the device to the PC which was fairly easy and tried to send a character from the PIC to the PC. It wasn’t working. I hooked up a scope to the PIC and I could see the character going out but nothing on the computer. I decided to try the other way. I would have the PC send a character to the PIC. I hooked up the scope and found that the module was transmitting on its RX pin. The silk screening means to hook up the RX pin to the silk screened RX pin. I usually don’t label my pins like this. I label their function rather than what to hook up to them.
With the pins straightened out I hooked up transmit and receive and had an echo program working in short order. I did notice a bit of lag after the module had fallen asleep. It took a bit of time for the module to wake up and start responding. But after that the module worked well, I am impressed by it.
To get the module to work you just have to put power to the module and have your computer seek for devices. It should show up on your computer. The access code to the module is 1234. The default baud rate on the module (HC-05) is 9600 Baud 8 data bits 1 stop bit and no parity
I would highly recommend these modules for a wireless application.
I hooked one of these modules up to a KA102 to see how they worked and what the current draw might be. I have a wireless sensor that I designed around the KA102 which draws 5uA in sleep. I was wondering if I could get close to that using the Bluetooth serial adapter. I have the ability to turn off the transmitter on the wireless sensor. I’m not sure how to turn off the Bluetooth adapter. Here is the schematic I used to run the Bluetooth serial adapter with the KA102.
It has been too long since I looked at this. I did another schematic not remembering that I had done the one above. I did wire up the circuit and tested it. It worked great. I just had some issues with the firmware. I was trying to use the firmware I used in the temperature sensors and that firmware sleeps thus, everything is turned off and nothing works. I changed the firmware a bit so that it didn’t sleep and it seems to work now.