Firmware Mods for Hot-Wired Thermocouple

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goofyboson
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Firmware Mods for Hot-Wired Thermocouple

Post by goofyboson » Thu Nov 15, 2018 5:28 am

I'm trying to push my hotend temp to 450 C, so I've got a k-type thermocouple and amplifier with analog output. Is there any reason I can't hot-wire a GT2560 to take my thermocouple readings on one of the open ADC pins (say ADC12)? This will require some firmware changes (updated temp_0_pin in pins.h, and new temperature table, anything else?), and if anyone has any details on this process I'd greatly appreciate not having to learn it all from scratch.

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_kaktus_
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Re: Firmware Mods for Hot-Wired Thermocouple

Post by _kaktus_ » Thu Nov 15, 2018 2:09 pm

Hello.
:mrgreen:

This high temperature may require reconstruction of the control system. Higher current may be required for the heater. She may not survive this.

These are only theoretical considerations.
This is a very interesting experiment. :D

I can draw your attention to the MAX6675 chip. It greatly simplifies high temperature measurements.
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goofyboson
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Re: Firmware Mods for Hot-Wired Thermocouple

Post by goofyboson » Fri Nov 16, 2018 11:08 pm

Thanks Kaktus!

What do you mean by control system? I think this is what I'm trying to do. If I can get the board reading the thermocouple and appropriately converting into a temperature, the PID should take care of the rest, no? Of course I'll need to beat down any noise and tune the PID settings, but this should be fine.

Heater power seems adequate. I just bench-tested a spare 30 W heater cartridge and got to ~520 C before it ran out of juice. Nothing even caught on fire!

As far as amplifiers go, the MAX6675 uses serial communication, which I think would be much more difficult to hack onto the GT2560 control board I'm working with. I've got the AD8495, which provides an analog signal that can just be read in on one of the open ADC pins, if I can solder a lead directly to the MCU. Obviously the analog signal together with the 10-bit ADC is going to limit my resolution, but I'll cross this bridge when I come to it, maybe tweak the amplifier output to prioritize the temperature range of interest or something.

Next I'll try to solder a lead directly to the MCU, and try to get the firmware to read the thermocouple. It looks like if I just change the temp_0_pin designation in pins.h and assign a new temperature table I should be good to go; am I missing something? Also it looks like most of the temperature table are just {ADC,temp(C)}, but what's this OVERSAMPLENR thing?

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Re: Firmware Mods for Hot-Wired Thermocouple

Post by _kaktus_ » Sat Nov 17, 2018 4:10 am

goofyboson wrote:
Fri Nov 16, 2018 11:08 pm
Thanks Kaktus!

What do you mean by control system?
....
It is necessary to program the operation of a new type of sensor.
When I read the rest of your conversation, I see that you are aware of it. :D

No matter which solution you choose will be good when it works reliably. :roll:
I will also add that the temperature reading from the MAX system is simple. You get a ready result.

That's why I wanted to draw your attention to it. But I did not look at which µC outputs are free. :roll:
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PaulAndrews87
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Re: Firmware Mods for Hot-Wired Thermocouple

Post by PaulAndrews87 » Fri May 17, 2019 1:48 pm

It is hard to give an answer to this as we do not know how the amplifier is set up... it may only be set up to take a temperature range of 0 – 200 degC... Without this information, it is hard to tell.
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