Bluetooth temperature module

posted Dec 10th 2010 12:43pm by Mike Szczys
filed under: home hacks, Microcontrollers

Wanting to know the outside temperature, [Jamie Maloway] built his own temperature sensor that can be read with a Bluetooth device. Let’s take a tour of the hardware above from right to left. There’s a linear voltage regulator with two filtering caps and a terminal block to attach a 9V battery or other power source. Next there’s an 8 MHz crystal and it’s capacitors, followed by a programming header on top and a 1-wire temperature IC, the DS18B20 we’re all familiar with hanging off the bottom. These both connect to the 8-pin PIC 12F675 that drives the system, and transmits using a Bluetooth module from Sure Electronics. Since this is using a serial protocol and transmitting ASCII data, it can be read using an automated script, or simply by using a terminal program.

Now, who’s going to be the first to get rid of the battery and leech off of the mains through inductance?

Comments [10]

tagged: 12f675, bluetooth, DS18B20, pic, sure electronics, temperature

10 Responses to Bluetooth temperature module

bogdan says:

December 10, 2010 at 1:15 pm

The idea is great, because it allows for reading on various types of devices. But given the limited range of the bluetooth i see no real advantage to getting the data on a computer/phone to that of having a dedicated receiver showing the temp.
I am also very very curious what the expected battery life is. My guess is that it is not that much…
@Mike Szczys as the sensor is designed to measure outside temp, i suspect there is very limited power available through inductance coupling…

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bogdan says:

December 10, 2010 at 1:17 pm

LE: it appears that the sensors you mentioned use the network line to communicate via very low power RF but are still powered by batteries.

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George Johnson says:

December 10, 2010 at 1:21 pm

Good timing, I wanted to do some stuff with BlueTooth.

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Peter says:

December 10, 2010 at 1:42 pm

I would have reversed the BT module end-for-end, so the antenna was away from the circuitry on the main PCB. I wonder why he chose to position it like he did?

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bemis says:

December 10, 2010 at 2:14 pm

@bogdan

I think the idea is that you may want to log the temperature data–or have some custom alarm action perhaps? But may not want to have to specifically run a communication/power wire to the site being sensed.

I can imagine this being useful to measure the interior temperature of a garage, basement, chest freezer, etc … anywhere within 20′ of so of the receiver.

In fact, I was going to do something quite similar to monitor a vacant house, but ultimately found that since I was using a webcam to watch for motion at the front door I simply mounted a large-digit LCD thermometer next to the door–there’s no alarm action possible based on temp, but it’s good enough.

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pff says:

December 10, 2010 at 3:46 pm

biggest waste of copper clad board award goes to this guy

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jukus says:

December 11, 2010 at 4:21 am

@pff troll elsewhere

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st2000 says:

December 11, 2010 at 9:49 am

@Jamie
Where do you guys find the specs for these boards? I have a broadcom (BCM 2024) based bluetooth HID keyboard module I want to move to a real (not thumb sized) keyboard. But hesitate because of unknown pins coupled with unknown devices on the keyboard’s PC card.

@pff
There are specifications for these bluetooth modules requiring minimal spacing of conductive material around the antenna. But in the end, most say no metal is better than some. I might have rotated the bluetooth module 180 to place the antenna nearer to the edge of a plastic case however.

@bogdan
Love the idea of simply placing a thermometer in view of the camera! Nothing beats the simplest solution. If the temperature is constant (i.e. you want to be alerted to any change) you might check out zoneminder. Its motion analysing software might pick up the changes in a 7 segment display as motion. I imagine you can even mask off the unit digit and only be sensitive to the 10′s digit if you want less resolution (i.e. by only being sensitive to motion in certain parts of the image). FYI zoneminder is not a commercial product but rather a use it and cough up some money if you find it useful.

@Jamie
“Since I don’t have access to a hot-air rework station…” Consider the ubiquitous alternative, a hot air gun. I say ubiquitous because types that can melt solder can be found in craft and archiving stores – which just seam to be ubiquitous in their own right.

@Jamie
You picked Bluetooth SSP. This probably makes this incompatible with Apple iPod devices which (I think) only works with Bluetooth HID for similar purposes (yes, I know, Apple does audio, but that’s yet other types of Bluetooth). It would be interesting to have a portable thermometer and portable logger combination to carry around.

@Jamie
Funny, I don’t see SSP or HID mentioned in the SURE data sheet. How did you know which type of Bluetooth the SURE module would use?

@Jamie
(Last Question)
I am lead to believe the MCU in these Bluetooth chips are programmable. The BMC2042 chip on the module I have boasts an Intel 8051 core. Did you look into programming your temperature code directly into the bluetooth chip and skip over using the PIC?

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Dante says:

December 12, 2010 at 1:30 pm

Great idea, i want to make one like this.

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pall.e says:

December 13, 2010 at 8:22 am

I’ve been thinking about making a kitchen computer out of an old laptop that doesn’t have serial. Been trying to think how I could mount it and still get info from across the room. Was looking into wireless usb but this would be cheaper.

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