Archive for January, 2010

Reprap extruder heater

Wednesday, January 20th, 2010

My cheap polymide tape arrived from Hong-Kong yesterday so I was able to get the heater built on the extruder for the reprap. No problems with the construction of the heater itself, although after running some tests I discovered the thermistor I had chosen is only rated to 155 degreees Celcius. I obviously wasn’t looking very hard when I ordered it or perhaps it was just the fact that it was one tenth the cost of a more suitable device that convinced me to buy it. I should have a new thermistor in this week and replace this one.

Before going too far with my heater I wanted to test the system and check that the temperature measured was accurate. I ran three sets of tests. Using the Butterfly Logger with some DS18B20’s and a SHT71 I logged the temperature of the barrel at the edge of the extruder (see close up above). The SHT-71 was used to monitor the extruder temperature with the DS18B20’s monitoring ambient. The first test was logged at 10 second intervals with the later two logged each second.

TEST 1
The first test was a 0.2 deg C/s ramp from near ambient up to 75 deg C and then a step change to 100 deg C and then passive cooling. This is shown in the plot below. The period of 10 seconds seemed too slow to give me a good idea of the stability so n the following tests it was decreased to 1 second. This did show rough correlation between the set temperatures and the measured temperatures although not really as accurate as I had hoped.

TEST 2
This test was a controlled ramp of 0.2 deg C/s from near ambient up to 100 deg C. After holding at 100 deg C the system is passively cooled to 50 deg C. The system holds at 50 deg C momentarily before being given a step change to 100 deg C, after which the system is allowed to cool to ambient.
The better time resolution allows the system stability to be better assessed. The system looks reasonably stable at the 100 deg hold mark. Here it is cycling around 5 deg around the set point. The ‘stable’ temperature is slowly rising which I attribute to the thermal mass of the barrel and thermal barrier warming up. It is not 100 deg C as it is not measuring at the same point where the control thermistor is measuring. Looking at this initially lead me to check the characteristics of the thermistor I was using and is what lead me to discover that it was only rated at 155 deg C. In checking the data sheet I also noticed a diference in the Beta value fromt he look up table used in the extruder firmware. I recalculated the look up table accordingly and repeated the tests in test 3.

TEST 3
This was a repeat of the previous tests with the new lookup table ( Beta = 4400). This seemed to give a ramp rate twice of what was programmed (0.45 deg C/s compared to 0.2 deg C/s). The temperatures seemed hotter which is expected given the change in thermistor table for the control firmware.

The next test will of course be to see how the system performs when loaded i.e. extruding some plastic.

Reprap Electronics build

Sunday, January 17th, 2010

I ran out of time this weekend to get anything done on the MP3 shield or the MLMC projects. I did however manage to find time to solder up the electronics for my reprap I’m building. After a couple of hitches I also got the firmware on and up and running.I had to download the latest from SVN else I got a clash between the stepper-motor drivers and the servo motor drivers in the firmware for the extruder.

I built the mother board to use a standard PC power connector even though I’m building a reprap. It just seemed silly to power this PCB via USB and then rig the power-supply to power all the other boards. I temporarily used the USB 5V to power the PCB via a pin on the JTAG connector during programming the firmware. Before the firmware on the mother board was programmed the PC PSU wouldn’t fire up so I needed a temporary power supply.

I managed to test the extruder board with some test software I found at http://objects.reprap.org/wiki/Microcontroller_Firmware_Hints#Driving_Steppers_with_the_Extruder_Controller_V2.2_.28Arduino_inside….29. But I haven’t managed to get it working through the mendel firmware via the host software yet. The thermistor was working so I know the RS485 link is functioning properly. Probably just a configuration.h option I’ve over looked.

It took a couple of hours to get the three boards all soldered up and tested. I’ll post more when I have more done. I’ll probably be focusing on the mechanical side of building the Cartesian robot for now so not much electronics left to do, although I still have the firmware to sort through…

[EDIT] It turns out that I had overlooked the I2C connection between the motherboard and the extruder board. I should really have read the instruction.

New PCBs in from BatchPCB

Tuesday, January 5th, 2010


My order of PCBs from BatchPCB arrived the week before Christmas so plenty of soldering and things to keep me busy over the holiday. I’ve also been distracted of late with building a reprap, although I’ve not got much further than amassing a number of PCBs, components and motors, watch this space for details as the build progresses.

My Batch PCB contained a new version of the Arduino MP3 board with provision for running from the 5V Duemilanove Arduino and a number of MLMC boards so I can string them together for testing. Unfortunately the ArduinoMP3 PCB had a couple of design errors, which is typical when your working on a design off and on over a course of months. The design will probably be released soon, but the libraries and demo code are also proving slightly more difficult.

Some changes to Hardware.
The basic design of the board is the same, VS1011 and SD card shared on the SPI bus with a 5 way Joystick on some digital lines.

I forgot about the TX/RX lines being shared with digital 0 and 1 on the arduino so I’ve had to re-route signals using those pins to the previously unused analog/general IO pins.

A couple of changes related to running the circuits on a 5V / 3V3 system. My Butterfly MP3 system that I based this on was powered from a single supply rail of 2.8V. The FTDI USB chip on the arduino was originally used to provide a 3V3 supply to the shield. I thought the 50 mA stated in the data sheet would be enough as my butterfly mp3 system only used about 50mA including processor and display. Unfortunately the is a large current draw when an SD Card is inserted causing the FTDI chip to reset and breaking connection with the PC. Although not a big problem I decided to add an LP2981 LDO regulator to supply a 100mA for the card and MP3 player circuits. If you don’t want to use this then you can not fit the parts and easily bypass with a jumper wire.

C++ing the libraries
I was hoping to use the existing libraries for the Arduino and SD cards to access the MMC/SD Cards and provide demo code to show using the shield. For an as yet unknown reason the existing libraries from Adafruit wave shield do not work. In order to test my hardware I have converted my MMC and FAT libraries from the ButterflyMP3 project to C++ for use with the Arduino system. I few teething problems and issues as I remember how C++ works and I now have a working SD Card system. Output from my current software is shown below

I’d like to use the already available libraries as they offer FAT32 and extended features over my bare bones implementation – so not quite ready to publish any finished code just yet.

Next step is adding the support for the VS1011. Again not quite as smooth as I’d hopped but moving along with the help of the old intronix logic port. Currently the VS1011 is not setting up correctly. Occasionally it plays OK but mostly nothing or a very slow version of a song, indicating to me the clock registers are not being set correctly.

I think another weekend or so of work and I’ll be there but if you’d like a copy of the current PCBs or Arduino files then just drop me an email or leave a comment.

Current Demo Software Terminal Output

TEST
0
MMC_RESET returned 0
MMC_SEND_STATUS returned 0
MMC_SEND_CID returned 0
0: FE 02 54 4D 53 44 30 31 47 28 9A CF 7B 33 00 7A ..TMSD01G(...3.z
1: 83 08 8E FF FF FF FF FF FF FF FF FF FF FF FF FF ................
MMC_SEND_CSD returned 0
0: FE 00 2D 00 32 5B 59 83 D6 7E FB FF 80 16 40 00 ..-.2[Y.......@.
1: FB 5E C9 FF FF FF FF FF FF FF FF FF FF FF FF FF .^..............
MMC_Capacity returned 1037952
MMC_Name returned 0 SD01G(
MMC_Read returned 0
MMC First Sector:
0: FA 33 C0 8E D0 BC 00 7C 8B F4 50 07 50 1F FB FC .3........P.P...
1: BF 00 06 B9 00 01 F2 A5 EA 1D 06 00 00 BE BE 07 ................
2: B3 04 80 3C 80 74 0E 80 3C 00 75 1C 83 C6 10 FE ...<.t..<.u.....
3: CB 75 EF CD 18 8B 14 8B 4C 02 8B EE 83 C6 10 FE .u......L.......
4: CB 74 1A 80 3C 00 74 F4 BE 8B 06 AC 3C 00 74 0B .t..<.t.....<.t.
5: 56 BB 07 00 B4 0E CD 10 5E EB F0 EB FE BF 05 00 V.......^.......
6: BB 00 7C B8 01 02 57 CD 13 5F 73 0C 33 C0 CD 13 ......W.._s.3...
7: 4F 75 ED BE A3 06 EB D3 BE C2 06 BF FE 7D 81 3D Ou.............=
8: 55 AA 75 C7 8B F5 EA 00 7C 00 00 49 6E 76 61 6C U.u........Inval
9: 69 64 20 70 61 72 74 69 74 69 6F 6E 20 74 61 62 id partition tab
A: 6C 65 00 45 72 72 6F 72 20 6C 6F 61 64 69 6E 67 le.Error loading
B: 20 6F 70 65 72 61 74 69 6E 67 20 73 79 73 74 65  operating syste
C: 6D 00 4D 69 73 73 69 6E 67 20 6F 70 65 72 61 74 m.Missing operat
D: 69 6E 67 20 73 79 73 74 65 6D 00 00 00 00 00 00 ing system......
E: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
F: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
10: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
11: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
12: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
13: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
14: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
15: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
16: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
17: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
18: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
19: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
1A: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
1B: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 03 ................
1C: 37 00 06 03 C3 E6 F3 00 00 00 0D B3 1E 00 00 00 7...............
1D: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
1E: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
1F: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 55 AA ..............U.
0
SECTORS PER CLUSTOR 20
BYTES PERSECTOR 0200
FAT Init returned:0
SECTORS PER CLUSTOR 20
BYTES PERSECTOR 0200
FAT boot Sector info
FAT begins at sector 244
Clusters begin at sector 768
Sectors per cluster = 32
Root dir starts at sector 736
THESTR~1.MP3 00045 037A00 2E0F
THESTR~2.MP3 00124 03400 2E1A
THESTR~3.MP3 001F5 025C00 2E24
THESTR~4.MP3 0028C 030400 2E2E
TWINSE~1.MP3 0034D 051B249 2E39
THEWHI~1.MP3 00494 03867AF 2E45
THESTR~5.MP3 0057B 02FE00 2E51
THESTR~6.MP3 0063B 032B00 2E5C
THESTR~7.MP3 0079 034D00 2E68
BEASTI~1.MP3 007DD 02EC9A4 2E74
BEASTI~2.MP3 00899 02E93C3 2E80
BEASTI~3.MP3 00954 01F172F 2E8B
THESTR~8.MP3 009D1 03A300 2E95
THESTR~9.MP3 00ABA 02DC00 2E9F
THEST~10.MP3 00B71 02F00 2EA9
THEST~11.MP3 00C2D 026900 2EB4
05-ILE~1.MP3 00CC8 02E8C16 2EBD
BEASTI~4.MP3 00D83 03EF2C9 2EC8
Files: 18
1A
DONE