Increasing the Range of a Wireless BBQ Thermometer (rev 2)

This Instructable will describe a very simple process for increasing the range of a wireless BBQ thermometer.

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

So on with the instructions...

Step 1 Gather Materials and Tools

1.) Materials
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:
http://astore.amazon.com/johspro-20/detail/B000SN7J7Q

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
f.) Superglue

Comments

[fritzlmon]

This worked slick! Very informative and practical.
Question- can you give a resource or formula for figuring out appropriate antenna length in relation to the mhz value in a given device? This would be useful info for other projects where I might want to extend the range.
Thanks!!

[waterstreet]

Great Instructable! I would not have attempted this without your instruction. Alas it did not work for me so I am trying to figure where I went wrong. In my first attempt, my belief was that the antenna on the board was the metal layer under the green and I soldered to that, even though the metal was silver colored and not copper. Since that didn't work, I thought there may be a copper wire running under the silver. Not finding anything, I re-soldered my antenna and ran enough solder between the gap. In my two attempts, the distance readings still remain the same as if I had done nothing and an obstruction like the window of the sliding glass door hinders it greatly, and passing thru a wall is impossible. Is there some test I can do with a multi-tester to see if my antenna that I added is functioning ? Do you have any other comments where I might have messed up? Thanks for any help!

[PAPADOC]

What I would like to have is a large display. Have you considered tapping into the leds to get large leds? I would like a display of about 2" numbers. I would like them to be mounted at right angles to each other such that they would be visible for 180degrees. Would this be feasible? I realize adittional power would be required. However, it would be nice to look from 60' away to see the oven temperature and the meat temperature.

[siliconghost]

That could definitely be done as an add-on or replacement to the existing LCD, but it would be a much more involved project. It would probably require the use of a microcontroller (like an Arduino) to hijack and re-interpret the LCD output to drive LEDs.

[DarkNovaNick]

Thanks a lot for this instructable! It was very detailed and things went exactly as they should have. It really didn't take very long at all. Before the mod, mine had a range of about 15 feet (through one sliding glass door), after the mod I tested at least 100 feet through 3 or 4 walls.

[Paul03]

FANTASTIC!!!! I do a lot of smoked pulled pork, sometime 12 hours of keeping at 225-250 temp. I live in a 'recycled' log cabin from the late 1700's. The logs are 12" thick and the farthest from the smoker I could get inside was about 10' from the wall. After adding the antenna I EASILY can set the receiver 30' down to my living room. You my think this weird, but I used a length of electronic solder for the antenna! I was so excited to try this and I had no small wire, but it works GREAT! Thanks again! But will say, it's a job that requires patience and some experience with working on fragile wires, etc. Also, without the instructions I would have forgot the o-rings!

[nmm01]

This works very well! One note, after sanding the antenna for soldering, I put my ohm meter on the antenna and probed around. Screw 1 as shown in step 3 connects to the antenna via the pcb. You could potentially attach the wire to screw 1 without having to sand/solder. I have not tried this, but maybe the next person to do this could try it first to see if it works. Thanks for a great instructable! btw, for those that tried attaching an antenna to the receiver side as discussed in the VirtualWeber forums, this worked better for me. YMMV. Neil

[siliconghost]

nmm01: That would bypass the two inductors (L5 & L6) for the antenna. While I considered doing exactly that, I didn't want to bypass anything when adding this antenna.  It may work but I'm not sure.

- John

[Scubabubba]

Such a simple solution to such a common problem. The best thing about this is your advice on the FCC search -- I have all sorts of small wireless devices that the circuit diagram would be helpful for. Thanks! Is there room to add a retractable antenna? Radio Shack sell replacement antennas for radios and remote control toy controllers.

[siliconghost]

As an FYI, I later put together the following Instructable focused only on the FCC search.

See HERE and thanks again for your feedback!

- John

[siliconghost]

Your the third person today to say they loved that piece about the FCC search! Glad I could help! I thought about a retractable antenna but none of the ones I had in "stock" were small enough. It is pretty tight inside the case. You could probably find an antenna that could run along the outside or back of the case. I'm not sure if that would help or hinder the range though. Some antennas are designed to work at specific frequencies. This operates at 433MHz (again, info I extracted from the FCC search). That plain ole' piece of wire seems to work pretty good for this frequency but maybe I'll try something else in the future and compare the results. I've also been told that you can "tune" to the ideal frequency by slowly cutting the wire down and testing after each cut. If I had better equipment (such as an oscilloscope) I could probably figure out the exact length that would be ideal for this device. Oh well, it works great for me now as-is! Thanks for the feedback! - John

[darita]

silicanghost...
Did the mod and it works, but I'd really like to find a retractable antenna. Have you had any luck with that? It can even be one that sits on the outside of the unit.
Thanks for the mod. Derek

[siliconghost]

Darita,

A retractable antenna would be nice. That was actually in my original plans for the mod (I still have the antennas which I bought from Radio Shack). After I researched it a bit, I learned that the antenna length should be matched with the frequency of the crystal for best performance (and in some cases, for it to work at all). Most people said to just try a wire which is what I did. It worked so well that I didn't bother looking into the retractable antenna again.

The overall length of the antenna from the top of the case out should as close to 6.7" as possible (as per my calculations anyway). Try finding a retractable antenna that meets those specs and see how it works. Note that your jumper between the circuit board and the antenna needs to be very straight, and cleanly soldered. Bends and spikes in a cold solder joint can affect the overall impedance and as a result, the overall performance.

I say give it a try and report back on how it works!

[darita]

thanks for the reply. FYI, there may be a new ET73 in the works, with a 300ft range, among other improvements. I'll let you know when I know more. Thanks again,
Derek