# True wireless thermometer



## jet_deck (Feb 6, 2008)

I have almost finished a Stumps clone, with a 3 shelf rotisserie.  (Not a spit)  I need a wireless thermometer, the current "wireless" design has wires which will get tangled in the rotation of the shelves.  Any ideas?


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## fatback joe (Feb 6, 2008)

Will this work?  It isn't 100% wireless, but is made for rotisserie action.

http://allyoucanupload.webshots.com/...54754113566108


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## packplantpath (Feb 6, 2008)

If I'm understanding you correctly, I suspect you may be out of luck unless you spend some real money.  You want a thermo that has the transmitter and everything as heat-proof so it can be put inside the pit with the probe in the meat?  Remember, batteries don't like heat, and I doubt the transmitter signal makes it through the metal of the grill.  

Best bet is if you are real mechanically inclined to make a setup where the probe wires can rotate on a pivot of some sort.  Kind of like the new system on big rig tires that keeps an air hose attached to the tire and keeps it pumped up based on the engine air compressor.  Good luck.  Maybe somebody else will have a better idea.

EDIT:  Here is one guys solution.

http://www.bbqsource-forums.com/invb...?showtopic=892

But I'm guessing it won't work if there is a shelf like yours and not the spit.


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## jet_deck (Feb 6, 2008)

That one is for a "spit" type rotisserie.  Mine have shelves that rotate.  Think of sitting on a farris wheel, and you being the meat.  Your chair rotates as is goes around, as does the support arm that holds your chair.  Wires sticking in the meat can get tangled in the chair and the arm.  Thanks for the quick reply.


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## richtee (Feb 6, 2008)

A slip-ring setup. Engineering, but it'll work. Mount a disc that rotates with thedrive sprocket made of 2 metal discs attached to an insulator. Connect probe wires to discs, and brushes to pick up the signal and send to the stationary tx.


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## kratzx4 (Feb 6, 2008)

Way to go Richtee. I was thinking the same. should be easy for one (1) probe but I think if you need more than (1) one it will take some design effort.


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## richtee (Feb 6, 2008)

Concentric rings I guess... well, at that point I'd make a circuit board outta a heavy copper and thick 'glass substrate. Could possibly get maybe 4 probes going in a 6 inch disc, allowing for slop in the drive, etc.


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## jet_deck (Feb 6, 2008)

sounds complicated, but i guess we agree, that there is nothing commercially available that we know of.


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## richtee (Feb 6, 2008)

You'd need some good quality brushes, bronze or something, and you'd have to keep the contacts clean... but here's a crappy drawing.


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## bwsmith_2000 (Feb 6, 2008)

Richtee,
     I don't know if it will work (resistance in the brushes etc.) but a good idea! I'm not even involved but points to you anyway just for your effort.


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## richtee (Feb 6, 2008)

That was my worry, BW, and thank ya kindly, Sir!

Being a fairly tight resistance delta T- it might not fly... but it might too. This is where MY fun begins  hahaha!! I'm an engineer who's a tech at heart!


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## jet_deck (Feb 6, 2008)

I appreciate your help, your 110% above anyone, anywhere else that i have posed the same question to.


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## geek with fire (Feb 6, 2008)

Not sure if it would transmit once you got this done, but what about enclosing a standard wireless oven transmitter base in an insulated box, with the probe hanging out of it.  Wrap the transmitter in insulation and seal the box.  Put the whole setup on the shelf with the meat you are measuring.  If your pit is around 250 or less, I would think you would be ok.

Now using it while cooking chix might be out of the question when you are in the 350 range.


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## richtee (Feb 6, 2008)

It's just the probe Geek. Assuming we can get a reasonable resistance reading thru the slip rings.. nothing has been done to the Tx.


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## geek with fire (Feb 6, 2008)

No, that's not what I'm saying.  I'm saying take a standard wireless probe (like the cheap $19 single probe maverick: http://dealspl.us/Maverick-Remote-BB...nd-Timer_46875), and build a heat protective box around the base.  Run the probe through a hole in the box and set the box on the rack with the meat on it.  The actual monitor is outside the the pit communicating to the transmitter inside the pit.  As I said, the only problem I think you will have is the drastically reduced range since you will be behind 2 enclosures (your protective enclosure and the pit itself); both most likely insullated.  However, I have this thermo and it really has good range, so it will at least go through the boxes and let you set it on a shelf near the pit.


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## richtee (Feb 6, 2008)

Ahhh...O-tay. Hmmm   just don't get  a plateau on a brisket..  ;{)


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## setitandforgetitsmoker (Feb 6, 2008)

i agree with yo ritchee on the split ring concept i have also worked with these. this is how a rotating beacon operates for a airport light. i dont think that this idea will work with these temp probes. i am more familiar with the type j etc. thermocouples.(basicly the same temp probes used in these remote thermometers) that are very sensitive to any types of splice let alone rotating brushes. for those of you that dont know these thermocouples are simply two wires made from two different metals. the differential from the heat is measured in omhs the converted in your thermometer to deg f. by trying to install brushes if you could figure out a way to calibrate and convert the omhs after the brushes (to deg in faren). you may be able to do this but as brushes wear and other variable come into play i dont think that it would last long. as to the idea of installing a remote thermometer on the rack with a heat shield i think this might work for a little while but i dont believe that you would get any type of time out of these units at these temps. one thing at this time to suggest to you is to mount your rotating motor on the outside of the pit leave enough room between the pit and motor for some little shelves to set your units on.make the outside wall of the pit rotate with the racks just my two cents.


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## richtee (Feb 6, 2008)

What would you attach the shaft to?


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## setitandforgetitsmoker (Feb 6, 2008)

from the center shaft in pic i would extend it out far enough to make connection to electric motor. use coupling to connect direct. then i would cut a round piece of plate and connect to racks fill in the rest of out side wall with steel and a flange around circle. i would mount the motor with steel brackets from fixed part of side wall on the base that the motor is attached to i would put a similar pillar block bearing to carry the weight of the racks. then when racks turn so does outside of pit and your wires and probes.also the horizontal support holding the bearing would have to be cut back to the outside of the rotating circle


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## richtee (Feb 6, 2008)

I'm missing something here. Seems ya stil got one end of the shaft floating. Got a pic?


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## setitandforgetitsmoker (Feb 7, 2008)

one end is in the pillar block on the opposite end of the motor the other end of the shaft is mounted on a plate with the motor which is is two brackets angled from the fixed part of pit the brackets are carrying the weight of the racks on one end other end can be left as is.


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## kookie (Feb 7, 2008)

I get what setitandforgetitsmoker is saying. I think this is basicly what he is getting at. Going off of Jet deck's pic of his pit. On the side facing you, extend the shaft and move the bearing out and mount on a bracket that is mounted to the up rights and not the top tube. Now you can mount a plate or bracket on to the shaft itself to mount the transmiter on it and run the probe wire down the shaft and tie it to it and then you can use the probe on the shelves. Make sure to leave some slack on the wire. This way the transmitter is outside the pit housing and it rotates with the shaft. I think this should work.

Kookie


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## richtee (Feb 7, 2008)

Ahhh. Small hole in the side. 'K.


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## setitandforgetitsmoker (Feb 7, 2008)

ritchee tried to upload a small drawing and it would not let me but kookie was close to what i was trying to get at. i would also look into a temp controller of some sorts with multiple thermocouple inputs it would not be used for temp control but would be a alot easier than messing with multiple units and i have found thermocouples on pid units to be more accurate that remote temp probes. hope this helps thank you


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## richtee (Feb 7, 2008)

I guess you could also break the rings and attach probes to each section, "Multiplexing" your readings from multipe probes to a single Tx. Dunno the stabilization time for the Tx to get a reliable reading, but it's not like the carosel is spinning 30 RPM or anything..Hmm  @ 1 rpm 3 probes, just shy of 1/3 min connected each, maybe 18 seconds.

As far as contact resistance, with a phospor-bronze brush, it would be minimal, but I do agree this would be the sticking point of this arrangement.


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## minichef (Feb 7, 2008)

Let me chime in about the sensor theory. You can have 3 standard types of sensor, thermocouple, RTD and thermistor. The thermocouple as mentioned is dissimiliar metals that produce a voltage (talking milivolts here) not resistance depending upon the temperature they are placed. With thermocouples you need to worry about the junctions you create after the probe junction, this causes error in your temp reading. The error will depend upon the temperature difference between the two points. If the only other junction is at the temp control no need to worry as the controls should have compensation built in to eliminate this error.
RTD and thermistor are resistive sensors, as the temp changes the resistance goes up or down. I would opt for RTD or thermistor sensor for the slip ring idea, less sensitive and easier to cancel error.

Just my thought,


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## richtee (Feb 7, 2008)

And most digi's use the RTD/thermistors I believe. I honestly think this will work. Keeping the contacts outside the smoker proper will increase it's reliability as well... Per Setit-.


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## jet_deck (Feb 7, 2008)

This is a block of Calsil. I cut a piece of it about the size of a kids shoebox, then cut it in half long ways, and hollowed out an area in each half, so that the Tx portion of the unit would rest in it, protected from the heat, and just let the wire and probe run out of the heat protected "box"
To test, last night, put the oven on 450*, and put the probe in the hollowed out block and left it for 30 min, it was not an accurate test, because the "L" shaped probe was larger than the hollow area, and i had about 1/8" gap between the two halves with the probe in between. After 30 min, the probe read only 130. I figure on a hot sunny day, beside the pit the Tx would be almost this hot anyway. Will try to test again tonight.


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## richtee (Feb 7, 2008)

Like I mentioned... a brisket or stubborn butt'll go durn near 20 hours... maybe with multiple units you can swap out during a mop...


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## jet_deck (Feb 8, 2008)

I hollowed out the Calcil properly for the probe to fit in.  Oven at 400*, probe showed 130* and climbing after only 20 min.  I guess i could back the oven down to 250 and see what happens


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