While the process should be similar for almost all RF thermometers, the specific model I'm hacking is a "Maverick RediChek Remote Wireless Smoker Thermometer Model ET-73". It can be purchased from my Amazon store here: http://astore.amazon.com/johspro-20/detail/B0000DIU49
This is functionally a fantastic remote thermometer. It has two temperature probes (one for food, one for smoker) with completely independent alarm settings. It's consistent downfall (as you may find from numerous user reviews) is range. Maverick claims 100' which I have verified to be true providing both the transmitter and receiver are outside and in line-of-sight of each other. As soon as you step in the house (or even behind a tree when far away) the signal is either blocked or range is drastically reduced. Other than that, most people seem to like it. This hack solves that problem.
Hopefully this will help some of you out. From start to finish this took me about 30 minutes. I would expect it to take 1 - 2 hrs if you're not familiar with the parts or basic electronics hacking.
Note: For those of you already familiar with "rev 1" of this Instructable, "rev 2" adds the following:
- Found and implemented ideal antenna length - 6.7" (based on whitepaper found here)
- Added antenna tube cover to protect exposed wire (and add to overall durability)
- General clean-up of the overall Instructable
Step 1: Gather Materials and Tools
a.) 6.7" of 22 gauge copper or steel wire
The antenna will require 6.7" of 22 gauge copper or steel wire which is commonly found at craft stores and used for flower arrangements. 22 gauge is perfect because it will bend and stay in place. You can coil it up for storage and point it out straight when in use.
Why such an exact length? Because antenna length is directly tied to the operating frequency (433.92Mhz) in which the device was designed for. There is a specific formula used to calculate the length which is what I used to derive 6.7". You still may get improved performance with a longer or even shorter antenna, but it won't be maximum efficiency.
Ideally the wire should be non-coated. If it is coated (as mine was) you will just have to sand the paint off one end for soldering.
If you need to buy something I would look for 22 gauge non-coated copper wire, something like this should work great:
b.) One Antenna Tube
In addition to making the project look very professional, the antenna tube protects your wire from breaking off, reduces strain on the PCB, and helps keeps water out (of the antenna hole). While any standard hobby antenna tube can be used, this Instructable is based on one from Dubro Racing, Model 2338 (Red, with cap). It can be seen and ordered here: http://astore.amazon.com/johspro-20/detail/B000BP4JC4
Finally, it is assumed that you already have a thermometer that you are willing to hack (which has obvious risks such as breaking the device if you're not careful). If you want to purchase a thermometer I highly recommend the same one I used (Maverick RediChk Model ET-73) here: http://astore.amazon.com/johspro-20/detail/B0000DIU49
2.) Tools Needed
a.) Soldering Iron (along with flux and solder)
b.) Sandpaper or some type of file (an emery board would even work)
c.) Wire cutters
d.) Drill (or Dremel Moto type tool) and small drill bit (1/8")
e.) Very small (jewelers sized) Philips screwdriver