3 digit 7 segment LED temperature display?

My initial question (I've scoured the internet and have found nothing) is, Has anyone made an analog temperature controller with a 3 digit 7 segment LED display that is ABOVE 125c? More specifically about 200c?

I join multiple printed parts together and fill cracks partly by using a soldering pen, but the soldering pen will get too hot and starts burning the plastic. There are variable temp. solder irons and "how to" tutorials on how to make my own using a dimmer switch, but nothing that displays a temperature.
I'd also like to install it on my hot ends. There have been some complaints about people's printers burning down from overheating. This would work independently from the printer's controller but hopefully on it's 12v PSU.

If nothing else. Can someone hack one of those $10 car thermometers to read higher temps? Something like this.

Lets answer some questions:
YES. I can program a microcontroller to do this. I can follow online tutorials, but I have to figure out how to modify it to reach the temperatures I want to reach. But why would I do that myself if it's already been done. Hence my question. Has anyone done it?
No. I'm not going to connect it to my printer's board and monitor it with my computer. I print a LOT. This wouldn't be practical. (I like to be able to take my parts from my shop to the front room and watch TV while I work)
Yes. I can buy the variable temp solder iron or use a dimmer switch and set it to when it starts to melt the plastic. I've already thought about doing that. That helps my burning problem but doesn't answer my question to view the temp.
Yes. I can use a food or IR thermometer. That would become awkward, expensive, and impractical to use. The display doesn't stay on long enough to monitor the temperature.
No. I'm not going to just set the iron to plastic melting temp and leave it at that. Why? That isn't helpful to make or find a temperature sensor of reaching at least 200c. Each plastic has varying melting temperatures and is not consistent across the board. (I hear enough complaints about some of the smells, doesn't bother me though)

... I'm controlling my hotend with an industrial temperature controller from Watlow which can handle and display temperatures below zero (with coolers insted aof heaters) to above 1000 degC with 1/10 degC resolution.

Some years ago I've developed some temp-sensors+drivers with PT100-thermistors for temps from 50 to 600 degC for a special application.

Should be no problem to control a 7-segment-LED-display or LCD's from the controller ... this is done regularly with the Arduino+Display-kits ...

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Viktor
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Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]

Hmmm. Yeah. Maybe I didn't write a long enough description about what I'm after.

I'm not trying to control the temperature. I'm just interested in a thermometer with display to reach the temperatures I want. Hooking up an Arduino just for that purpose is a little over kill.

Quote
KingRahl
Hooking up an Arduino just for that purpose is a little over kill.

... why?

If you have a spare 7-segment- or LCD-display, then a small Arduino (e.g. a Boarduino) is something below 10€ here in Germany ...

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Viktor
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Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]

Oh, smaller, that's more like what I would have thought. When you said Arduino, you meant the "family" of Arduino and not like an Arduino Mega (overkill). Thanks for the suggestions.
That information will be very helpful.

I know this may seem like overkill and the form factor may not be what you're after, but why not a PID temperature controller with a K-type thermocouple? They're cheap and readily available. It is a controller, yes, but you don't _have_ to use it to control the temperature, just read it.

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[3DKarma.com] - suppliers of quality, affordable 3D printer kits and filament for the UK market.

i think this is kind of cool, the led display would be able to be seen from farther away especially if it is jumbo sized. you could use the same arduino library to update the display, and small capacitors to hold a charge until next refresh, saving a bunch of money doing it that way! i would suspect that capacitors that hold a charge for 100ms would work fine, or you could use latching 8bit shift registers for each segment, reducing overall pin count.

At first I was wanting something like this.
But I wanted to know the actual temperature.

So I found one with a digital display circuit here.
Which led me to here and here and finally here. In the Automated wood stove video, he mentions he used an exhaust gas temperature gauge. I couldn't find one less than $30.

So now I'm going to go with 3dkarma's suggestion with something like this one. That's a price and useful operation that I won't need to make my own now.

Now those heater alarms got me thinking about those people whose RepRaps burned up. This sounds like something useful. An independent system to help from overheating. Maybe connect it to activate a shut off on the PSU. At least with an alarm so you can stop it manually and put out any fires that may have started if you don't get to it in time. This way you don't have to wait for your smoke detector to go off only after the fire has already started and burned your machine half down.

Thank you everyone. It helps discussing things with others, I was trapped in a cycle that kept me from looking for other methods than what people have already made.
I was hoping to be able to keep it small and be able to use a thermistor though.

Edited 2 time(s). Last edit at 07/23/2014 08:53PM by KingRahl.

I believe with Marlin firmware you can connect two thermistors to your hot end and it will shut the hot end down if they disagree by a wide enough margin, meaning if one comes loose (which seems to be a common failing), the firmware will shut the hotend down instead of letting its temp skyrocket and eventually cause a fire.

An alternative that's been discussed here, I think, is to use a thermal fuse / thermal cutoff.

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[3DKarma.com] - suppliers of quality, affordable 3D printer kits and filament for the UK market.