Week 6 Assignment: Redraw the echo hello-world board

       

1. After watching both of Jeremy Blum's Eagle Tutorials I experimented with the EAGLE interface (after downloading it from the Cadsoft USA website, selecting the "Freeware" option), and began to get familiar with it's various features.


2. Even though both of Jeremy Blum's tutorials were very thorough, learning a new methodology, that too in a new subject like Electronics Design proved quite daunting! I revisted some Basic Electronics concepts from our Remote Guru's Week 6 webpage to get a better understanding of what I was doing to begin with.


3. I attempted to define the basic electronics components we'd be using for the design of the board in question:
   
   • Battery = A form of Power Source; usually represented in the form factor of a "Cylindrical" e.g. standard DC 9V battery, 1.5V nominal voltage AA batteries, etc. or "Button Cell" (also known as coin cell). Battery types are usually distinguished by their "battery chemistry" which could range from Li-On; Lead Acid and many more varieties
   • Capacitor = A form of temporary "Electric Charge" storage, not really a battery, but similar to the function of a battery, where the capacitor's energy is generated/stored by electric fields. The role of a Capacitor in an electronic circuit is primarily to provide as "another voltage source" where common use cases include "using to pass higher frequences" or combined usage with other circuit elements to provide functions such as oscillation, fluctuation-bypass, etc.
   • Resistor = One of the most basic electronic components, usually used to limit the flow of current or reduce the level of voltage in a circuit. Resistors are primarily used to "balance load" in a given circuit -- as the purpose of creating the circuit in the first place (electrical or electronic, etc.) in itself is "to power some kind of load".
   • Pushbutton = A form of "Switch". A pushbutton's role in an electronic circuit is to provide a switching mechanism, which either results in interrupting the flow of current through the circuit, either by allowing it to pass (ON state) or not allowing any current to flow (OFF state)
   • Diode/LED = From its definition a Diode is a circuit element which allows electricity to flow only in one direction. An "ordinary diode" can play several roles in a given electronic circuit -- ranging from acting as a one-way switch to acting as a "rectifier-of-sorts". A Light Emitting Diode (LED) is a special type of diode whose function is to "make light" of a certain wavelength. LEDs are used in electronic circuits primarily to serve as Indicators.
   • IC = According to Wikipedia, an IC or Integrated Circuit is "a piece of specially prepared silicon into which a very complex electronic circuit is etched using photographic techniques". 'Nuff said ;)


4. Outlining the roles of the circuit elements above put me on the right course to conceptually understanding what I was trying to do! I think after one reflects on "why" they need to "do what they are being asked to do" --> a light suddenly emerges from the (proverbial) tunnel. I proceeded to take another stab at the EAGLE software interface.
• We were instructed to download the files: fab.lbr and fab.dru and place those files in the directories: /
• Having installed Eagle in Step 1 of this sequence, I proceeded to create a new "Project" from the default /eagle folder and edit its description:



• After creating a new project on my installation of Eagle; I went about initiating a SCHEMATIC where right from the start I clicked the "Library --> Use" option to import the relevant library files (I selected every single .lbr file in the /lbr repository)
• I did have a few problems accessing the fab.lbr library within Eagle, even though I had correctly moved the original file into the /lbr directory of the Eagle installation -- I had to close and re-open my project a few times; even re-start my machine; until I was finally able to "see" the fab.lbr listing within the file tree. After this issue was resolved I was successfully able to "Add" the requisite circuit elements to my Schematic:



• The (new) Billing of Materials mapped to the following EAGLE library part names:



Element/Part Description	Corresponding Part Name	Library	Quantity Used
10k Resistor	RES-US1206FAB	fab.lbr	2
500 ohm Resistor	RES-US1206FAB	fab.lbr	1
ATtiny44 IC Package	ATTINY44_SSU	fab.lbr	1
1uF Capacitor	CAP_US/CAP_US1206FAB	fab.lbr	1
20 MHz (3-pin) Resonator	RESONATOR	fab.lbr	1
FTDI header pins	FTDI_SMD_HEADER	fab.lbr	1
ISP pins	AVRISPSMD	fab.lbr	1
LED	led/LEDFAB1206	fab.lbr	1
Pushbutton	6MM_SWITCH6MM_SWITCH (OMRON SWITCH)	fab.lbr	1
Power Supply (+5V)	Supply1/+5V	Supply1.lbr	1
Power Supply (GND)	Supply1/GND	Supply1.lbr	1



• In order to understand the existing connections in the original echo hello world circuit, I looked at the "board" level layout (picture above) and tried to trace the connections between the various circuit elements. I came up with "paths" which indicated how the various elements were connected to each other:
• Vcc [ATtiny44] --> R1 [1] --> C1 (+ve) --> Vcc [FTDI] --> > [AVRISP]
• R1 [2] --> PB3 [ATtiny44] --> RST [AVRISP]
• C1 (-ve) --> GND [ATtiny44] --> GND [AVRISP] --> Resonator (ground)
• C1 (-ve) --> G (blk) [FTDI]
• PB0 [ATtiny44] --> Resonator (input)
• PB1 [ATtiny44] --> Resonator (output)
• PA6 [ATtiny44] --> M0SI [AVRISP]
• PA5 [ATtiny44] --> MIS0 [AVRISP]
• PA4 [ATtiny44] --> SCK [AVRISP]
• PA1 [ATtiny44] --> Rx [FTDI]
• PA0 [ATtiny44] --> Tx [FTDI]

I added two more paths to the above list which incorporated the addition of the new button and new LED:

• PA3 [ATtiny44] --> Button --> R3 (10Kohm) --> Vcc
• PA7 [ATtiny44] --> R2 (10K) --> LEDFAB1206 --> GND


• After pressing the icon which allowed me to switch between the Schematic View and Layout View, I tried to re-arrange the components according to the original echo hello world layout view:
  
  
  
• I realized then I couldn't "net" each of the components to each other in Layout view; so had to switch back to Schematic view and manually net them to create the right connections. Having played around with the component libraries of the Schematic View, I managed to "layout" the schematic in such a way that I could distinguish between the different connections:




5. As I again switched to the Board view, I proceeded to re-align each component in iterations to see how best to route them eventually:

                       

                       

6. Rather than manually routing each path from scratch, I decided to try the Autorouter function in Eagle first, so that its algorithm could optimize the paths between each of the components. I input the following parameters when performing the Autorouting function:
   - Top: *
   - Bottom: N/A
   - Effort: High
   

                                   

7. As soon as the autorouting had finished I still ended up with 2 unrouted traces/paths (both emerging from the FTDI Header):




8. In the confusion of trying to autoroute all the components, I noticed I had used the incorrect AVR ISP header in my schematic --> which subsequently caused the incorrect placement of a through-hole AVR ISP header (instead of the SMD variety). I corrected this as shown below -- however, my routing problem had still not been solved!