heated bed thermistor with G3 electronics?

Hello all

I wonder if anyone could tell me whether or not there is a connection for the heated bed thermistor using Makerbot G3 electronics?

Specifically, I am looking for another position where I can connect a second thermistor or thermocouple to measure the actual temperature of the nozzle at the business end when heating it since the extruder thermistor will be on my heater block.

I see some have mentioned using D6 somewhere, but I was wondering whether there is a ready connection somewhere... looking at the extruder controller schematic it seems D6 is not currently used - marked as extra??

I am using Reprap host and it does have a return for the heated bed thermistor so I wonder if I need to do anything besides attach the thermistor and ensure the correct table is attached...

can anyone please advise?

thanks.

ps. Merry Christmas all

Yes, use A6 on the extruder board:

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Bob Morrison
Wörth am Rhein, Germany
"Luke, use the source!"
BLOG - PHOTOS - Thingiverse

Hi Bob

I saw this diagram but am confused as the relevant section on the extruder controller v2.2 says the signal pin is next to the letters whereas the above diagram indicates the signal pin as on the opposite side.

Anyway, would the heated bed thermistor be connected between GND and Signal or VCC and Signal? - I expect GND.

Also, the theory section of the thermistor page implies a resistor should be added as a splitter so the voltage difference can be measured which then gives the resistance of the thermistor - allowing you to determine the temperature.

Do I need to add resistors etc. or do I simply attach directly to the Pin 6?

Finally, my heater ran for the first time last night and as the temperature climbed I saw the heated bed teperature rise as well?? nothing was attached...?? anyone comment on this?

You need all three connections: GND, Signal and VCC.

You need a Temperature Sensor v2.0 Kit (or similar).
The thermistor is connected to two pins on the Temperature Sensor board, the board to GND, Signal and VCC of the extruder controller.

The pins are marked wrong on the board, the image in my previous post shows the correct labels.
Apply power to the board and you can verify which pin is GND and which is VCC. The remaining pin is Signal.

Edited 1 time(s). Last edit at 12/28/2010 12:21PM by rhmorrison.

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Bob Morrison
Wörth am Rhein, Germany
"Luke, use the source!"
BLOG - PHOTOS - Thingiverse

Thanks Bob

Just to clarify my reading of the schematic JP1 is GND, JP3 is VCC and J2 is Signal?

Using the link you (Bob) gave me I searched the reprap wiki for the board and found the page here. Reading this it seems that the board can be substantially simplified.

IMO R3 and the LED are optional - just there to indicate power is applied to the board.

It also indicates R1 (1k) is optional. Can anyone clarify the use of this resistor?

That leaves the capacitor (which I assume is to keep the signal clean?) and R2 which on this board is 4.7k. Does anyone
know how to determine the resistance value to use for a particular thermistor?

Nice and easy to make - and thanks to my scatter-gun approach of buying a range of resistors and capacitors last shopping spree I have the required components

R1 is only needed if the thermistor cannot handle 5V without heating itself too much. 100K thermistors are OK on 5V but 10K are not.

The value of R2, assuming no R1, should be about the resistance of the thermistor in the middle of the range of temperatures you want to read. See [hydraraptor.blogspot.com]

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[www.hydraraptor.blogspot.com]

I wish I knew about this board before. I followed Adrian's instructions on connecting a Mendel heated bed and it used a similar circuit for connecting a thermistor in addition to a power mosfet for the heater. I could have saved some time with this kit instead of a breadboard.