How to upgrade TechZone board from thermocouple to thermistor?

Hi there,

Has someone already upgrade the TechZone Remix Electronic so has to use a thermistor instead of the thermocouple?
What are your thought about this upgrade? Is it worhtwhile?

Regards,
Loïc

[1] TechZone_A-D_With_OneWire
[2] Generation_3_Electronics/Tech_Zone_Remix

To do this, all you need to do is to load another firmware to the extruder controller that uses a thermistor and connect a thermistor. The thermocouple AD is a good idea since thermocouples are more accurate and they can go to higher temperature than thermistors, but because it uses serial communication between the chip and the EC, it's too slow. So, it's better to just use a thermistor. The problem is finding a recent firmware that works. I upgraded to RAMPS months ago but at that time, I was using a 5-D firmware that I modified from a July 2010 release.

Thanks for your fast answer!

But to what should I connect the thermistor? It seems the DS2760 is useless in this configuration...
Indeed the thermistor change its electrical resistance, whereas the thermocouple change its electrical potential difference, aren't they?

Moreover, is it precise enough to wrap the thermocouple around the Heaterblock compare to the thermistor being immerged?

Thanks again.

Regards,
Loïc

The terminals for the thermistor is labeled "Temp" in the extruder controller board. It can go either way since it's just measuring resistance.

You should insert the tip of the thermocouple in the same hole in the heater block where you would insert a thermistor.

The information on that wiki page may help you too : [reprap.org]

I see no reason to change to a thermistor personally, thermocouple works fine for my needs. It's just a little more tricky to attach to the hot end, but on the other hand it's more robust than a thermistor.

The reason that I switched from TC to thermistor was because it was randomly losing temperature during a print. I think TZ addressed this by having their modified version of SF resend the M104 command periodically. But even with the thermistor, my prints were stopping at random points. This might have been a 5-D firmware issue or a HW issue with the remix. This all went away when I switched to RAMPS.

Edited 1 time(s). Last edit at 11/22/2011 11:21AM by brnrd.

I have had some random stops during prints with monotronics, but not so often. I noticed they often happen when another electrical device is triggered on (hair drier...).

I'm now pluging my board power on the same UPS my computer is using, it got rid of the random hanged prints.

Note this may not be related to your issues brnrd

I was asking just because our first extruder "burn". Something went wrong and the thermocouple was getting red hot! Indeed the wires went too hot and because of a slight defect, there was a connection between the thermocouple and heater wires.

So we bought the new extruder head (the one for Geared Adrien bowyer extruder), but it comes with a thermistor. Obviously connecting the thermistor instead of the thermocouple does not work!

Unfortunately time to get a thermocouple is longer and more expensive than buying a thermistor (in France) hence the question.

Thanks all.

DeuxVis: TechZone's tip manager ended up being one of those fantastic ideas that turned out to be seriously flawed. The problem isn't the hardware, it's that the serial communications between the extruder controller (or monolithic board) and the "tip manager" are very poorly written.

It takes 40ms to read the temperature from the tip manager, and for most of that time, the "OneWire" library that handles its communications keeps interrupts disabled. The routine that times the serial communications does so by disabling interrupts, and "spin-waiting" the processor. This approach to communications can only be described as stupid, or possibly evil, as it can have very negative affects on anything in the firmware that uses interrupts.

Quote
loic.fejoz
So we bought the new extruder head (the one for Geared Adrien bowyer extruder), but it comes with a thermistor. Obviously connecting the thermistor instead of the thermocouple does not work!

You can try installing one of the 5D firmware that came with a 2010 version of the reprap host in the repository. You might need to load the same version of the MB and EC firmware since the communication between them changed with the addition of support for a heated bed. But I don't know when it started.

If you find that the temperature of the extruder varies too much (oscillates), then you might need to play around with the PID parameters or just switch the firmware to bang-bang control. I uploaded a version that does this in another thread, but it had the extruder motor control commented out. If you need this, post again and I can upload one with the extruder motor enabled.

Quote

This approach to communications can only be described as stupid, or possibly evil, as it can have very negative affects on anything in the firmware that uses interrupts.

The problem is OneWire has some strict timing requirements that can only be met with interrupts disabled, so it is an unsuitable hardware architecture for this application.

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[www.hydraraptor.blogspot.com]

Ah, I had the exact same problem with my first techzone hotend assembly - luckyly the thermocouple did not die, I disconnected it fast enough.

I got some replacement thermocouple by the meter on ebay from england - quite fast and cheap, and I'm in France too. [cgi.ebay.fr]

Works fine with my techzone huxley.

loic.fejoz Wrote:
-------------------------------------------------------
> I was asking just because our first extruder
> "burn". Something went wrong and the thermocouple
> was getting red hot! Indeed the wires went too hot
> and because of a slight defect, there was a
> connection between the thermocouple and heater
> wires.
>
> So we bought the new extruder head (the one for
> Geared Adrien bowyer extruder), but it comes with
> a thermistor. Obviously connecting the thermistor
> instead of the thermocouple does not work!
>
> Unfortunately time to get a thermocouple is longer
> and more expensive than buying a thermistor (in
> France) hence the question.
>
> Thanks all.

brnrd, nophead, thanks for the explanation. Trying to switch to another firmware is on my todo list. Question, can I still use thermocouple if I get rid of that daughter heat management board ?

Yes but then you will need something like this [reprap.org] to convert the thermocouple voltage into something an analogue pin can read.

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[www.hydraraptor.blogspot.com]

Thanks for the information. Given the price of the AD595 IC used, It's probably better to buy some thermistors then