Sally Williams @ Fab Academy 2015

Note: Assignment for Week 4 is to make a programmable micro-controller - also known as a FAB ISP.

Tuned in to regional reviews to learn from others process and development. This was followed in the afternoon with Neil Greshenfeld's introduction to Electronic Production.


Assignment: Making a programmer 

For Fab Lab tutorial, click here.
 
Preparation of board and sacrificial layer

In order to get the best result (a board milled through the copper to a consistent degree), it is critical that the board is placed upon a very clean surface with NO undulations that could change the depth of milling as the bit traces it's path. The board to be milled is placed on a 'sacrificial layer'. (At Fab Lab Manchester, this was a larger copper plated board used for its engineered precision). There was some residue of adhesive tape on this layer, and therefore this had to be thoroughly cleaned and brushed off with white spirit and cloth.

The board is adhered to the sacrificial layer with strips of double sided tape (pressed firmly down). It was important that no bubbles get trapped under the tape, and also that the tape strips were close together so that the firmest adhesion was made to the sacrificial layer.

   
Pressing sticky backed copper plate firmly onto bed at 0-0 position of sacrficial layer


   Roland Modela Milling Machine


Milling

The image below shows the trace file (hello.ISP.44.cad.) loaded into the control panel of computer terminal (Click here for link to files). I was using the mill trace defaults setttings for the Modela. This used the 1/64" end mill bit.

    



The end mill had to be zeroed on the x,y and z axis of the copper plate, then the x and y axis was given a 5 mm clearance of corner edge as a start position. It is important that the end mill bit, mills clearly through the copper plate layer of the board to remove any possibility of connectivity being made where it shouldn't.

Once the trace path was milled successfully, the 'cut out trace' path was loaded in the control panel.  This would cut out the boundary of the board from the rest of the copper plate stock to it's working size. The end mill bit used for cutting out on the Modela was 1/32" 

  Cut out trace path

Milled and cut out board

The board was deburred (from any splices of copper around the edging, and from any unclean milling). The board was then washed with a sponge to clean and degrease (from natural oils on fingers)


Soldering

Following the schematic drawing to solder all the components onto the board. I enjoyed this process, although a magniying glass was critical!

  

At the soldering station with my crown jewels, with soldering iron (300 - 350 degrees), solder reel, tweezers, copper cleaning braid tray, magnifier and extracting fan at hand. The copper cleaning braid and solder sucker were there in case it was necessary to remove solder when errors were made.




Just a little but proud at this point! (that's why the image is a little on the large size).

  Fab ISP

I tested some of the connections with a multi meter. The multimeter will show whether there is a voltage being picked up between two points. The multimeter proved the board to be clear of any shorting faults and ready for the smoke test and then programming.

For this sequence I successfully followed the 'smoke test'  on the tutorial here - plugging the FabISP into my laptop via the mini USB cable. I did NOT get an error message on my computer 'drawing too much power' so this further supported that the board was clear of any 'short circuiting'. Quite a relief.

I downloaded Crosspack and Xcode to enable the programming of the microcontroller.  I then followed the tutorial here to program the board.

The board was programmed succesfully!

Once programmed, the 0 ohm resistor and solder bridge were removed with the use of the solder removing tool.

The board is now ready for use over the following weeks at Fab Lab.