melzi malfunction

hi all,
I built a Mendel90 ordering not the full kit by nophead which was a mistake (nophead told me so). I got many components by some friends as a gift for the reprap beginning and I installed them in the printer. I am glad that everything works exept the measuring of the heatbed temperature which drives me crazy because I cant find a solution on that problem.
thermistors and wiring are ok, checked that by connecting the bed thermistor at the etemp. both thermistors together dont work. the temperature pronterface reads out of the bedtemp is correlating to etemp, heating the bed has no effect on the thermistor although the bed heats. I fear that the problem is on the Melzi which isnt v2 version.
is there a possibility to solve that problem without buying a new board?
please help me!
Sandmann

I think it will be a firmware problem. Are you using the Marlin from my github and the Melzi board support package that it contains?

I think I had a similar problem when I first used Marlin which I fixed by changing the pin definitions. There was a clash between the SD card and the bed thermistor I think due to two different ways of numbering the digital pins associated with the analogue pins.

---

[www.hydraraptor.blogspot.com]

yes thats what i use. but how do i change pin numbering and which pin should i use?
thanx for answering.
oh wait, support package? i am checking that.
sandmann
ps: in pins.h btemp is set to 10 sdss is 53.
and with support package.

Edited 2 time(s). Last edit at 01/10/2014 04:19PM by Sandmann.

That doesn't match with the pin numbers in my version of Marlin. TEMP_BED_PIN is 6 and SDSS is 31.

---

[www.hydraraptor.blogspot.com]

sorry pin numbering is correct. looked up the wrong board... its pin six

Edited 1 time(s). Last edit at 01/10/2014 06:46PM by Sandmann.

If you are using my firmware and selecting Melzi in the arduino IDE then it should work. AFAIK there are no firmware differences between different version of Melzi apart from some have the wrong resistor values. The ones I use are the original version with the correct resistors. The V2 uses a different stepper driver chip as RRP had supply problems.

The fault you describe sounds identical to what I got when I first tried Marlin on a Melzi with the SD card enabled. If it works with the SDcard support disabled then it is definitely the pin numbering issue that I fixed.

---

[www.hydraraptor.blogspot.com]

thats strange, I use your fork.how can I disable sd support for testing?
found it. but it doesnt solve my problem.
can I use the external pins header to give it a try with an external circuit? maybe the pin 6 is burned (not by me, I double checked bed wiring before I used it and checked a hundred times while trouble shooting...

Edited 2 time(s). Last edit at 01/10/2014 10:04PM by Sandmann.

There are analogue pins available on the expansion port, so yes you could add a 4K7 pullup and a capacitor, or you could cut a track and reroute the onboard signal.

However, when a pin is damaged it normally reads a fixed value. The fact it is affected by the other thermistor input implies some connection between them.

---

[www.hydraraptor.blogspot.com]

"or you could cut a track and reroute the onboard signal"
- I think I have no ability to do that
I go to the electronic shop for 4.7uF capacitor and resistor and give it a try.
oh it works.... I put a wire (which cannot stay there forever) between bed thermistor socked + and extension pin (no. 1) changed firmware and it works.

Edited 2 time(s). Last edit at 01/11/2014 08:39AM by Sandmann.