Sunday, October 17, 2010

Bluetooth Thermometer - Update!

'Morning Everyone,

I finally invested the hour-and-a-half and threw together a version of the Bluetooth thermometer on a small (45mm x 45mm) proto-board. Believe it or not it worked first time, which is quite amazing when you consider how much wire-wrap is hidden on the bottom side of the board.

On top you can see the Sure Bluetooth module on it's adapter board. It is attached to the base board by way of a 2.54mm female header receptacle, so I can easily pop it out and use it for something else should the need arise. The TO-92 device sticking out the side is the DS1820 1-Wire thermometer. It is attached to angled header pins so it too can be removed and extended if needed.

Hiding under the Bluetooth module is the PIC, 8.000Mhz crystal, some loading caps for the crystal (22pF), and 4.7k pull-up resistors for the /MCLR and 1-Wire bus pins on the PIC12F675. I didn't include an ICSP port was included for a reason - The PIC needs +5V to be programmed, and since the Bluetooth module runs off +3.3V it would probably end up getting fried if accidentally left plugged in while the PIC was being programmed. On the bottom of the board is an LM1086-3.3V LDO regulator, rated at 1.5A it is comically over sized for this application, but it's all I had lying around in my big box of miscellaneous parts, so that's what I used.

The Future
- Adding configuration features to the firmware (boot menu / options)
- Reducing power consumption (lower clock speed / better power regulation)
- Solar power supply and super capacitor (maybe not with this Bluetooth module though)

I do have a National Semiconductor LMX9838 Bluetooth Serial Port Module kicking around that I am hoping to use in lieu of the Sure module for the next iteration of this project. This would not only save PCB space, but also allow better software control and power management.

That's all for now folks - If you're interested in the firmware or hardware send post a comment and I'll make a conscious effort to draft up some schematics and cut-and-paste the firmware into the blag.

Right now I'm off to Future Shop to pick up a clock radio...

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