Wireless temperature sensor

Consisting of 2 circuits
One reads the temperature using a DS18B20 and then transmitts it over the radio waves.
The other receives the data and displays it.

I've not fully tested the range yet, but I've had it working over 12 feet going through 2 walls.

Transmitter Parts List:

• Picaxe 08m
• DS18B20 temp sensor
• AM RT4-433.9 transmitter module
• LED
• 4k7 resistor
• 1k resistor
• 3.5v Battery

Receiver Parts List

• Picaxe 18X
• AM HRR3 433.9 Receiver module
• 7 segment I2c module
• 5mm 2 pin Bi-Colour LED -- red and green

Step 1: Build the circuit

The diagram below shows the circuit to build. I apologies for the poor quality, I did attempt drawing it in Eagle at first, but didn't get too far and decided it would be quicker to just draw it in Ms Paint !

The transmitter circuit is shown at the top, I actually didn't use 5v, instead I ran it off a 3.5v button battery. The button battery was hooked up to a solar cell; a module I pulled from a cheap solar torch. I've had the transmitter circuit lying on my window sill, happily transmitting for a week with no power problems.
The AM transmitter/Receiver I had bought years ago from Maplin.

The receiver circuit is shown below, it is very simple. Pins 11 and 12 on the chip is actually a bi-colour LED, I wasn't sure how best to draw it.
The counter looking object in the top right makes displaying a number easy work. I needed a chip that could use the I2C, which is why I'm using a Picaxe18X. The 7 segment module was bought off ebay for about �15, but they do sell it on their website

I've not shown the programming header, partly to keep it simple and clean and partly because I was using a seperate circuit to program the chip.

Comments

[Costas.I]

Could you please modify the code to read temps from o to 100 oC?

Thanks,

Costas.

[manuka]

THOUGHT: Consider a simplified setup using just a single LED for the readout?! Coding to show tens as a long flash & units as short ( hence 23 Celsius would be long, long, short, short,short ) allows reading clear across a room, or even further at night ! Power saving will be quite significant ( as only a single LED needs to be lit) & just a PICAXE-08M can then be used at each end. Refer http://www.picaxe.orcon.net.nz/ntcswancode.bas for a standalone NTC thermistor based approach that's good to ~a degree Celcius.

Ok -the bare code is probably not enough ! I've hence now further packaged up that 'winking LED" approach as a downloadable .doc => http://www.picaxe.orcon.net.nz/NTC_thermo-Swan-code.doc Feel free to grab ( although credit appreciated)-it was recently used to good effect as a hands on activity with a High School electronics class here in NZ

EXTRA: New "M2" Picaxes have just been released - refer http://www.picaxe.com for details

[manuka]

(removed by author or community request)

[AndyGadget]

Hi Richard,  I'm looking to use those modules in a simple home security system.  What did you use for the antenna? The datasheet doesn't suggest anything but I think the logical choice would be a 13.6" (1/2 wavelength) wire.

^{(I suggest you re-enter your tags to appear as separate words.to make it easier for the search engine to find.)}

[scottinnh]

Very nice! I would love to copy this for myself (unfortunately I do not have a Picaxe cable and development environment). This is one of the few wireless solutions I have seen for the DS18B20. Thank you for sharing.

Typo? "4k7 resistor" means 4.7K resistor, or 47K resistor? I assume the former.

I see you have some ideas lined up for future revisions. If you are looking for suggestions, would it be possible to eliminate the Pic chip? (Timing could be replaced with an analog chip, but not sure about the data encoding...). If you have a Picaxe dev environment, these chips make perfect sense... but if you do not have it already, it might be cheaper to go with XBee (which is still not cheap). I'm looking for low cost. :-)

FYI - This other tutorial (one year newer than yours) is similar: http://www.dehnes.com/60/2010/02/09/wireless-temperature-and-humidity-sensor/

[scottinnh]

OK I was looking to replicate this, and all the usual Arduino parts seemed like overkill in both power in expense. But I didn't want to dabble in PIC so soon.

So I found this - the JeeNode wireless mini-Arduino ($22 complete!):
http://shop.moderndevice.com/products/jeenode-kit
It looks like all I would need is the temp sensor, and a power supply, and a home base receiver, and I am good! This will be for wireless temp monitoring of beer mash, and another for my kegerator. For portable power, there's lots of options but I'll just use a spare MintyBoost (and some power management on the 'duino).

This next part does not interest me at the moment, but FYI while searching on the "cheapest" wireless temp sensors that can be read (received) by a PC or Arduino, it looks like you can wire temp sensors directly into the serial inputs on an XBee or some Bluetooth modules (negating the need for a host processor). Not 100% sure how that works, but someone reading this might benefit. Cheers!

[zoltzerino]

Nice work, you really put some effort in to this. I admire the usage of wireless technology and readily available components. But, there is always a but, it is just so very cluttered, like spaghetti with a microcontroller garnish, I would love to see this entire project produced as PCBs and with proper enclousures. For the reciever were to boards really necessary, or ws this just to make it easier to work with. one last thing, try cutting your breadboard wirning down a little, just to neatent things up, especially when you accidentally start riping them out, tangled onto your watch (That REALLY annoyed me). I'd love to see this taken further.

[zoltzerino]

Excuse the typos, im tired, dont hassle me about the spell check.