Week 4 : Electronics Production

This week begins off with the Electronics part starting with Electronics production. Here we need to technically produce a circuit. There are several techniques to build a circuit right from breadboarding to etching to milling the circuit. In lab, we mill the circuit and then stuff it with the components.

Assignment :

This weeks assignment was to make a Fab (tiny)ISP Programmer.

FabISP?

FabISP is not a new word for me, but that was mainly due to me attending the Pre-Fab Academy workshop conducted in the Fab Lab. At that time, FabISP was totally new to me inspite of me coming from an electronics background. All that saved me was, DOCUMENTATION works of others!!! Yeah, documentation is important. The FabISP is an in-system programmer for AVR microcontrollers, designed for production within a FabLab. So, technically it's a way less costlier programmer (believe me, hardly cost's 5 dollars!) made in the FabLab, by the Fabber's, for programming the boards. During the prefabs, I made the Fab ISP Programmer version which requires an extra FTDI cable to plug into the computer.

What I did this week:

This week's assignment was already done by me during the Pre-Fab Academy workshop conducted in the Fab Lab. The Fab ISP Programmer version which I made during the prefab's requires an extra FTDI cable to plug into the computer. To avoid that extra cable, I've decided to take any of the USB versions of the Fab ISP and make it. I selected Valentin's board to mill, I liked the way the solid jumpers were just stripped off from the board once the make fuse was done.

The circuit and cutout files were downloaded for milling. For milling the circuit onto the copper clad circuit board, the machine used is Roland Modela MDX-20.

Insights regarding preparing the maching for circuit milling:

1. Preparing the machine.

Change the bed to metal bed. Milling board is very sensitive to height, so place a sacrificial layer underneath. Metal board is used instead of acrylic sheet as the acrylic sheet has irregular shape. Copper plate is used as sacrificial layer upside down.

• Do Not drop the Metal bed, this can cause bend in the metal bed. This can result in irregular milling.
• Use Double sided tape to fix the copper clad on top of the sacrificial layer. Take atmost care that air bubbles don't get trapped in between the layer. The air bubbles can result in the circuit board being unevenly placed due to which the circuit won't get milled properly.
• The copper gets rusted with touch. So, after milling take it for a wash to remove the rusting. Try not to use rusted plate for milling sensitive boards.
• The Drill bit 1/64 inch is used to mill the traces and 1/32 inch is used to cut the board out. Do not drop the 1/64 inch bit as it can break easily. Take extra care while removing the bit, use a sheet of thermocole underneath to prevent the breaking happening even if the bit is dropped to the workspace.

2. Fabmodules for Roland.

We use fabmodules to run the machine. As before, select the input format and output machine.

Input format: .png

Output format: Roland MDX-20 mill (.rml)

Select mill traces: 1/64

Load .png

If any rotation or image edition is done, then make sure that resizing of the image is done using resize .png. Invert .png is done to invert the color of the board before milling (in case needed).

Make path

Change the x(min) and y(min) position according to the space where you need to mill the circuit in the board.

And then click on Move to xmin, ymin button.

Make .rml

Sent it

A window appears showing the estimated time for completion of milling and button to start the process. Click on begin milling.

This will send the milling machine into action!

3. Traces, Cutouts

I used Valentin's board as Fab ISP Programmer.

I downloaded the traces and cut outs from here

Initially I cut the traces and then the cut outs.

4. Removing the cutout from the copper clad circuit board.

Take care that the cutout doesn't break while removing from copper clad circuit board. For this initially just slightly just jerk all the sides of the cutout to be taken and then gently pull out the board. Leave the excess tape that gets stuck below the cutout as it is, as I found it to be useful to hold the board in place while soldering the components. A small hack! :)

5. Stuffing

We are using smd components (yes, those tiny ones you solder on top of the board!). While gathering the smd's I found out that 18pf and 0.1uf capacitors were missing in the electronics inventory. So, I replaced them with 10pf and 1uf capacitors after refering to other Fab ISP boards and design spec's. While gathering the smd's I wrote the components in a paper and created a box in which I placed my components. This helped me in not loosing the components.

6. Soldering

By soldering, we place the components on to the pads in the cutout. Things to note down while soldering the components:

• Don't hold the components too hard with the tweezer. Then it would be the last time you see the smd.
• Start soldering the components from the centre and then along the sides.
• Keep the tip of the soldering rods clean.
• Never forget to turn ON the Fume Fan. Safety comes first.

7. Programming the ATtiny 44A

Before using the FabISP, you need to program the ATtiny44 on it. To do this, I used another (programmed) FabISP. It's also possible to used Atmel ICE or Arduino to program the Attiny44.

We need Avrdude (for programming) and GCC (to compile C code). To get GCC and avrdude on Ubuntu, I used tutorials from fabacademy, How To Assemble and Program the FabISP.

Don't forget to power the FabISP Board by using the 6-pin programming header

Download and UnZip the firmware.zip file from the Fab Academy Electronics Production page and move into the newly created firmware directory. Open the firmware directory in terminal.

Make Clean

Make Hex

Now go to the make file generate in folder and open it with text editor. Edit the line in the make file for your programmer. I am using usbtiny to program my board, so I uncommented the below line:

At first on make Program I had an error shown as below:

8. Removing the solder jumper.

For this just break the board at the cut out made. A disadvantage which I see in the board is that once the board is broke down, in case you need to configure the board again then it's not possible!

Final Board Shots:

Continuation of Flexible Circuit Cutting...

With the FabISP done, I decided to trouble shoot the problem I was facing while trying to cut a flexible circuit. After discussing with the pals out here, I understood that the problem was not with the force settings but with the adhesiveness of the bottom sheet. So, I removed the bottom layer and stuck the copper sheet onto a masking tape layer. This time the Flexible Circuit Cutting worked perfectly.

I was able to cut the circuit and remove the unwanted copper sheet parts easily. But I made a mistake by transfering the circuit to the wrong side of epoxy! (Oops, I had to restart the whole process again. Never mind, it was a big learning curve for me. Look before you Do!)

After transfering the copper trace on to the epoxy sheet, stuff the pads with the components as usual. Remember to start stuffing the components from the middle of the board.

The board with stuffing being done.

Final stuffed board