Irony problem

Perhaps, you should buy a nice soldering iron and put a card up at your local music shop offering to help electric guitarists change out their pickups and pots.  Then you might recoup your investment quickly and not have to worry about being out-of-pocket.

This one-https://www.sparkfun.com/products/12724 is analog/no feedback of real temprature and markings cannot give exact number thus not nowing the actual tip temp.

That's why I wrote-

plus I wanted a way to read the temp on screen and building something to that is impossible!!!!!!!!!!!!!!!!!!!(partly possible)

real temprature and markings cannot give exact number thus not nowing the actual tip temp

And your point is.?

You were given information earlier regarding temperatures and things that affect it, so what is a few degrees.

Some of your other questions lead some of us to wonder if you could undertake this safely.

Personally I will not give information that could be misread/not followed and thereby endanger someone .... call me names or whatever, but I won't be party to it.

Rather than ask us to do your project, you could always do your own project that detected the temperature, displayed it and controlled a light, which is the first part of this quest.

Who knows maybe it might be useful for some other project later.

You may also wish to start doing research (ie search the internet and read data files) on what you need to measure the temperature involved.

If I'm not mistaken a thermistor doesn't have a very good curve in those temperatures and over that range.

Hopefully you will understand that the physical building is a very small part of any project, and if you want to 'own' the project you need to do the work ... otherwise just buy one.

Mark

Questions of the quest

-Can a thermistor whitstand that temprature?

-For a soldering iron, how many watts do I require it to make it come near 500C

   royston dsouza

First, I am not sure why you would want to reinvent the wheel. But, that's not my business.

Newark Part No. 30F1725 ) might be an option for you.

Irons vary greatly by manufacture's, but it would be easy to say that 50 watt minimum would be required, probably more towards 100 watts.

Ben Heck's Home-Brew Solder Reflow Oven 2.0 - YouTubeTo get an idea of some ideas of where to go with this idea.

This thermistor is a particularly high temp version yet it has a maximum temperature of 300 C under his required range.

You will need a thermocouple or similar to operate near the desired 300-500C

The highest temp theoretically possible for a thermocouple is just below the melting point of rhenium.  One could fab an RTD out of tungsten, I suppose.  Beyond there spectro-optical techniques have to be used.  Pyrometry.

It seems to me that everyone is focusing on the wrong part of Royston's request.

Making a variable heat iron is rather simple. The problem lies with making a readout of the temperature.

royston dsouza wrote:

Is there a way to find the temprature (without a microcontrollers) and how many watts equals to 800F(to use with lead-free components like RPi)

According to Ben Heck's explanation of thermistors and thermocouples in the Home-Brew Solder Reflow Oven 2.0 (6:25 in) suggested by Lupe Lopez. Whether you are measuring the resistance of the thermistor or the voltage of the thermocouple, in order for the readings to be converted into temperature data, the only practical solution is to process it through a microcontroller chip.

Unless someone knows how to modify a $10 car thermometer with 3 digit 7 segment display, to display higher temperatures than 125c. The highest thermometer circuit I can find is 150c. Those use a LM35 or similar. The only other way I've found is to use a LM3914 chip in this video https://www.youtube.com/watch?v=JQzWSN9K3_c or similar type circuit. (circuit diagram link is in videos description) He mentions modifying indicated temperatures with a potentiometer.

Maybe replace each LED with a complicated circuit that activates a sequence of the 7 segment LED display for each number. This will limit the number of preset temperatures you will be able to display though.

One possibility would be to use a heat resistor. Just as we use electrical resistors to bring high voltages down to useable levels you can use a heat conductor like a strip of copper connected between your heat source and a heat sink. The heat flowing from the heat source to the sink will produce a gradient along its length. Pick a spot along the heat conductor that is within the temperature range of the sensor and attach the sensor there. Then it is a matter of calibrating our sensor reading to actual tip temperature and having the micro processor print out the adjusted temperature. Now before I say Voila' I have to say that this is more a thought experiment that a prctical solution. For one thing the heat resistor could adversely heat sink the tip unless it was very low mass. This would require more current to maintain tip temperature. The added sensor and heat resistor on the solder iron would perhaps make it clumsy and difficult to use. I would expect the data from the sensor would only be accurate in a very narrow band of temperatures unless there was a lot of processing being done on it to compensate for heat losses at different temperatures due to conduction and radiation. Temperature of the sink would have to be brought into the calculation also since, on a small poratble item like a soldering iron, it would surely not be stable. And the list goes on.

John

Yeaaaaaah.... That's not helpful at all. The temperature sensor would read the lower temperature. You would have to keep viewing a conversion chart or keep thinking about the difference on the other side of the heat resistor.