Tech Zone Extruder Board

We purchased the techzone generation 3 boards, and the seem to be working with one exception. The extruder controller seems to be ignoring the thermistor. The extruder gets more than hot enough to melt the ABS plastic, but it does not shut the heater down when it reaches the proper temperature. In addition, when we power up the extruder board, the temperature reading goes from T: 0 to T: 231-232, before we even turn the heater on. We don't know if this is a problem with the board, or if we need a special firmware or what.

Thanks in advance for any help.


EDIT: Another test confirms that the temperature reading goes up to 231 even if there is no thermistor attached. It looks like there is some sort of problem with the board.

Edited 1 time(s). Last edit at 07/27/2010 01:52PM by HSRepProject.

Or it is a problem with your firmware or thermistor. If 231 is the last entry in your lookup table in the firmware than the board is not getting a reading from the thermistor. Either that or your firmware needs to be updated to match the thermistor that you are using.

Have you confirmed that the thermistor is working by just measuring the resistance across it as the temp increases?

Davmj

It sounds to me like there must be some sort of short across the thermistor contacts. With mine (I have the techzone too) if I disconnect the therimistor I believe I get a really low reading either 0 or 2°C (this would make sense has high resistance = low temp). If it is not this then it could be that the thermistor look up table is wrong, did you change it from the default? I will check when I get home what the resistance across the contacts are without the thermistor plugged in.

JSR

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[jsrreprap.blogspot.com]

I have the Tech Zone boards too. What firmware are you using? The folks at Tech Zone told me that they use the RepRap host software and firmware from January and it is pretty stable. I have used that too and have had luck. I tried the firmware from July 19 but haven't gotten it to work right. that may be something I did though. I do know that sometimes I have to stop and restart the host software a few time before it reads.

Something I noticed in the last day or so is the a few times the host software (from January) did not initially pick up the temp but after I moved one of the axis it started working. I haven't tried it enough to know if actually works or if it was just a coincidence.

I have a similar thing. At the moment I have to restart the host software at least once (and usually reset both boards) before the extruder board comms work correctly, I thought I just hadn't worked out the correct starting procedure yet, but maybe it is something more fundamental.

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[jsrreprap.blogspot.com]

That trick with moving an axis seems to work for me most of the time.

I have also been told that using a thermocouple is more reliable than a thermistor. However, that requires another board so there is a little more cost with that. I haven't converted mine over yet so I can't speak from experience. The folks at Tech Zone are extremely helpful. I would suggest contacting them.

I also have an issue with the temperature not registering. I'll post again if I figure it out. I put my issue on a little page with a pic of the extruder here:
[anthong.com]

if anyone has a suggestion it would be much appreciated. It's painful to be this close to done.

thanks.

Why is your thermistor hanging off the side of your nozzle in free air? It has to be in good thermal contact with the metal barrel to pick up the right temperature. It works by conduction, not radiation.

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[www.hydraraptor.blogspot.com]

nophead, thanks for your reply... I follow a lot of your stuff. It's not exactly in free air, the makerbot thermistor has a clear coating around the end, it's a tear drop shape. it's actually in contact with the nozzle as best as I could get it with such a tiny nozzle, now I'm understanding why people do the bighead thing. maybe I should try and angle it so the tip points inward more?

I'm going to try and test the thermistor with a multimeter tonight, someone at the local hackerspace told me how.

thanks.

... nophead's right, the thermistor is more cooled from the surrounding air than heated from the nozzle!

You should use a smaller one and/or carve a grove in the side of the nozzle, fix the thermistor in the grove and isolate with capton ...

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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]

I tested my thermistor, it seems good, when I turn on the heat I see the resistence lowering gradually on the multimeter. I'm convinced I just need to try out some different firmware.

Just as a follow up, once I used the normal mendel extruder firmware instead of the one found on the wiki that said it was for the techzone board, it all worked.