Electronic Design

 

The goal of this weeks project is mainly to learn how to use an electronic design software. We were tasked to recreat the hello-world board and add some peripherals to be programmed. I used Eagle, which has a pretty non-intuitive UI but once you get the hang of it, itÕs not so bad (at least at the level of use I had this week).

 

Modeling Hello-World board

 

I began by coppying the hello world board.

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I made this schematic in a rush while trying to follow along with Jo who was giving a tutorial in our section. It was hard to do both at the same time and so this schematic is a bit hectic.

 

I tried the autoroute function in the board file but it just made a mess.

 

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I then routed the traces by myself (thanks Jo for the pointer to go inside the IC)

 

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It was now time to add the peripherals. The schematic was was really messy so I started over. Remade the board (I screen shoted my first one and then used it as a guide in the second.

 

I added the components to my schematic file (yes I forgot a resistor for the LED). I decided to add a microphone and an LED. My plan is to program it so that the louder the you speak / yell the brighter the light will get. I put a resistor in line with the mic both because I will need it to make a jump over a trace and because I thought I might need it to take out some noise in the signal. (I assumed that the elctret microphone would work like a potentiometer as I was about to finish my project Rob explained to me that that is not how it works. He said I might still be able to get some functionality out of it so I kept it for this week, I should have done more research first).

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But I couldnÕt get these new components to show up in my board file. After a while of googling I gave up and started the whole process over again!

 

Final schematic:

 

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Holding down the alt/option button allows you to move objects and connections on a finer grid allowed me to make my lines more clear. I then move to the board.

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Having already made the board without my new components I copied that design then found places to put the new components. In the picture above you can see what Eagle is calling an unrouted trace on a clearly routed trace. I had done this trace in the standard width of .016, I was worried that it would be too thick to fit through the FTDI port so I deleted it and redrew it at .01. When I did this that line reapeared, I couldnÕt get rid of it but it didnÕt matter for milling. This is a window into some of the wierdness (which iÕm sure there is some underlying reason for) of Eagle.

 

To export for milling I turned of all layers  except top. Then file->export->image. Set the DPI high, >1000 and select window (make sure all your traces are in the window).

 

To prepare for milling I opened the file in photoshop and cropped down the image to contain less background. Next I filled all the red lines to be white.

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After that I saved the image as outline so that I would have the identical formating to make my outline around and know that I would not cut into any traces. I drew the outline in white and then erased the inner traces.

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After the processes followed the same processe as week2 (http://fab.cba.mit.edu/classes/4.140/section.Harvard/people/Vizner/Week2/Programmer.htm).

 

Here is a picture of the board after milling

 

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The assembled list of parts

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I am a big fan of the write it out and use double sided tape system!

 

This time when stuffing the board I ran into a new challenge of how to attach some of the components to the board and almost did not have enough room! The microphone had a (relatively) large presence on the board and almost overlapped with the FTDI and JSP pins. I had to solder those down first then the mic.

 

 

 

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Also I used th resonator for the first time this week and it seemed to be much thicker that the components I had previously worked for. This presented almost a wall that needed to be soldered down. I think I did it rightÉ.

 

 

 

Here is the board all said and É stuffed!

 

 

I am excited to program it, and perhaps redo the microphone part, in two weeks!

 

Things I learned / You should look out for

á      Autoroute is not perfect and might make a mess and leave strange artifacts, make sure it is turned off if you choose not to use it.

á      Make sure you understand how all the components you are putting on your board are supposed to work, read the data sheets.

á      Holding down the alt/option button allows you to move objects and connections on a finer grid

á      When you add components you must take into account their physical size, this may become a constraint.