Exercise 4 - Electronic Production 19/2/2020 to 25/2/2020

There are 2 tasks for this week:

• Group Assignment: Characterize the design rules for our PCB production process
• Individual Assignment: Make and test an in-circuit programmer by milling and stuffing the PCB

Task 1: Characterize the design rules for our PCB production Process

This is a group assignment done with Noel Kristian and Yeo Gau Siong.
Our collective work is documented on the SP Fablab Website and hence only my learning and reflections are documented here

Task 2: Making and Testing an In-circuit programmer by Milling and Stuffing the PCB

Even though the assignment this week is simply to use one of the designs from the Fab Academy class site to make a working in-circuit progrmammer, being completely new to electronics, I have to spend numerous hours just to understand some very basic electronic concepts and to learn how to solder very tiny components.

I chose to use ISP design from Brian's site as the documentation was excellent and the tutorial is easier to understand and follow. The fabrication process can be broken down into several steps.

(A)    Creating the Milling Machine readable  (NC) file & cutting the PCB
Since the board layouts were already available from Brian's site, I only need to use MODS to convert the raster file into numerical control programming language format for the milling machine.

The method for doing this is the same as that for the milling machine characterization and hence not included here. The preview of the NC file is as follows:
After obtaining this file, the trace is cut using the StepCraft 420 Milling machine. The settings are captured from the mods screen below:

A 0.1mm 10 degree V-shaped drill bit was used.

(B)    Stuffing the PCB

Before soldering can be done, the "unwanted" or "dead" copper must be painfully removed using a penknife.

My local coach, Steven demonstrated a much easier way - By increasing the number of passes (each offset by 0.5 diameter, much of the "dead" copper can be cleared by the milling machine.
As I am a newbie to soldering SMD, my local coach Rodney, provided me a soldering training kit to hone my skills before stuffing the PCB.

After practicing for a while, I started stuffing the board using 0.6mm solder.

Components for the FabTinyISP are as follows:

1x ATtiny45
2x 1kΩ resistors
2x 499Ω resistors
2x 49Ω resistors
2x 3.3v zener diodes
1x red LED
1x green LED
1x 100nF capacitor
1x 2x3 pin header

Despite the practice, soldering such small parts for the first time was still very difficult and I made quite a few mistakes. Thankfully, mistakes are not irrecoverable. My coach, Steven demonstrated the use of the hot air gun to melt the solder on the PCB board so that the positions of the components can be adjusted or completely removed for re-soldering.

Serious Mistake!!

While soldering the 1K resistor, the solder went to the dead copper. In an attempt to remove the solder and the dead copper, I accidentally ripped the entire copper pad off the PCB board!

I have to redo the entire PCB from the beginning!

After 5 hours, the new PCB is finally stuffed. After my coach helped to check for short and rectified some bad soldering, I proceed with the third step: Software installation.

(C)    Software Installation

To program the completed PCB to function as a programmer, several softwares must first be installed. Following the guide from Brian's site closely, the following softwares were installed:

• GNU Toolchain - (from Microchip.com instead)
  
• GNU Make
  
• Avrdude - For Avrdude, the Avrdude.exe downloaded according to Brian's guide does not seems to work for my laptop, I have to install WinAVR from Sourceforge.net first and locate the avrdude.exe file from the Bin folder in WinAVR
  
• Firmware Source Code
  

After installing the softwares, I have to edit the windows search Path so that all the required software can be located when their names were type on the command line. To do this, I followed the guide from Brian's site again. (Control Panel -->System -->Advanced System Settings-->Environment Variables). The following 3 items were added to the search path:

• C:\Program Files\avr8-gnu-toolchain\bin
• C:\Program Files (x86)\GnuWin32\bin
• C:\Program Files\avrdude

Following that, I go to gitbash and carried out the following steps in the order as according to Brian's guide

• Connect the programmer to a USB port and type: avrdude -c usbtiny -p t45.

An error "Could not find USBtiny device (0x1781/0xc9f)" was found. This error was described by Brian in his guide. Following his instruction, I downloaded Zadig to check and update the USB driver installation.

• Run "make" under GIT. This created the fts_firmware.hex file and the fts_firmware.elf file.

After this step, I inserted the programmer into the USB port of the laptop

I run Zadig again and tried to install libusb-win32 driver and winusb driver, but both installations failed.

After troubleshooting, it was found that the header was not properly soldered and contact was intermittent. After touching up the solder, the PCB can now be recognized and I can continue with the software installation. In gitbash, I entered "make flash" to upload the firmware into the PCB (target).

This command upload the fts_firmware.hex file into the chip. The "make flash" command basically execute the avrdude program as per the command line "avrdude -c usbtiny -p t45 flash:fts_firmware.hex:i"

After running "Make Flash" the next step is to configure the chip using the "Make fuses" command. This command like "make flash" run the following avrdude command: "avrdude -c usbtiny -p t45 lfuse:w:0xE1:m -u hfuse:w:0xDD:m -U efuse:w:0xFF:m"

After this step, I inserted the PCB into the laptop usb port and to my delight, the device is detected and recognised!

The final step is to disable the reset fuse (or blow the fuse, as described by Brian). To do this, I have to run the command "make rstdisbl"

Resetting the fuse changes the ATtiny45's reset pin into a I/O pin. This action will disable the ability to reprogram the ATtiny45 chip in the future. To do this, the existing programmer is again used and my PCB is connected as the target.

The software installation is finally completed and my PCB can now be used as a programmer! I tested it on a target board and it worked!