The transcript about compiling Teacup apparently requires a working Teacup in another directory already. Maybe this is more helpful for beginners (edited transcript):
$ git clone https://github.com/triffid/Teacup_Firmware.git Cloning into 'Teacup_Firmware'... remote: Counting objects: 3911, done. remote: Compressing objects: 100% (1249/1249), done. remote: Total 3911 (delta 2827), reused 3689 (delta 2643) Receiving objects: 100% (3911/3911), 2.00 MiB | 624 KiB/s, done. Resolving deltas: 100% (2827/2827), done. $ cd Teacup_Firmware/ Teacup_Firmware $ git checkout Gen7 Teacup_Firmware $ cp config.teensy.h config.h Teacup_Firmware $ cp ThermistorTable.single.h ThermistorTable.h Teacup_Firmware $ vi Makefile # uncomment atmega32u4, comment out atmega644p Teacup_Firmware $ make CC mendel.o ...
Possibly. --Traumflug 11:55, 15 November 2012 (UTC)
Done. Tested on 2012-11-25 per http://reprap.org/wiki/Teensy_Breadboard#Compiling_Teacup_for_Teensy_using_the_Makefile -- DaveX 18:33, 26 November 2012 (UTC)
Wiring directly to a cheap ATX may inject 50mVpp of noise into the supply lines which end up feeding the ADC circuitry. With a 5V AREF, 50mVpp noise on a 10 bit ADC is about 10 counts. Adding filtering on the ADC sensor input/thermistor output does not solve the problem if AREF is left unfiltered. Using a lower noise powersupply may improve things. Filtering a noisy power supply through a LDO regulator or an RC filter may improve things as well, but I've not tested this. DaveX 21:09, 26 November 2012 (UTC)
The ATmega32u4 recommends a 10uH+0.1uF LC lowpass filter between VCC and AVCC to filter out >310KHz noise from the CPU switching. However the Teensy 2.0 does not have this inductor, instead connecting AVCC directly to VCC, and then through a 0.1uf to ground (http://www.pjrc.com/teensy/schematic.html)
You may do well by generating a well regulated external 3.3V, 2.56V or 1.1V source and using it to drive the thermistors and AREF, while setting "#define REFERENCE REFERENCE_AREF" in config.h. That should eliminate powersupply noise from the ADC inputs, leaving only digital noise from AVCC and noise picked up from the wiring.
Gen7 filters the +5 with a LC lowpass filter (fc=1/(pi*sqrt(100e-6*.1e-6))=100658Hz) for AREF, followed by a RC lowpass filter (fc=1/(2*pi *4700*10e-6)=3.38Hz) into the ADC inputs.