Milling FAB ISP

Milling Mechine

The machine at my lab is the modela mdx 20 by roland. This machine is operated from linux subsystem Ububtu through fab mod made by prof. Neil.

This time I milled the fab isp using attiny 45, this will serve as my programmer for other circuits that i will make.

The Process

1. First step is putting the PCB board in to the mill. Since its a single sided PCB , a single copper plated board is used. The material of this board is called FR1 . Now to make it stay in the board, a double sided tape is used. Always remember not to over lap the tape while pasting it as it can cause bumps that can affect your board.

Carefully place the board to be milled into the machine bed.

Setting the axis

Now, its time to set the axis. Now open the mod programs. X and Y axis is set by estimating the value and entering it into the mod options for X and Y axis such that the spindle over to the edge of the board. After setting the x and y, its time for z axis.

Setting the Z-axis

Now its time to set the z-axis. To do this we need to bring the spindle with 1/64 end mill bit near the board using the down button. Be careful not to hit the bit into the board while pressing the spindle down button. After placing the spindle just over the board we need to loosen the screw and slowly place the end mill onto the top of the copper PCB board. Now carefully tighten the screw and remember not to over tighten it.The machine automatically remembers the Z axis along with the one you entered in the mod.

Well, now the machine is ready to print some PCB for you.

2. Now its time to start milling the board. Though this board can be designed on eagle or any electronic circuit designing software, I have used the already available designed in the fab academy web site.For milling PNG image is used and the reason is because its possible to get good resolution in PNG than other softwares. Now after setting the machine's axis , all thats required is to load the png into the mod and after checking the setting as per your requirements , just press the send it button and press start milling in the next window request.

The time varies with different circuit boards. For mine it took around 15 mins with 6 offset and the remaining of the setting were kept in default.

Cutting out

Now the next step is to cut out the milled PCB. To do this , we need to load the outline png and set the mod for cutting. We also need to change the bits to 1/32. After changing the bits set Z axis following the same process. The default setting worked well for cutting my circuit board. Also remember the to keep the X and Y positions. After all these checks, press the sent it button and press the start miling in the next tab. It took me 1 mins to cut the circuit out.

Change the 1/64 end mill bit to 1/32 end mill bit.


Now my circuit is milled and the next step is to solder

Now its time to solder but refer to the circuit diagram for right orientation of the components like LED and zenner diode. Before soldering the main board i have practiced on faulty and damaged board. I started by collecting all the components that I need for the ISP.
Check once if all the components are working or not by using the multimeter.

Now its done

On to Programming

I programed my board using the windows system. There were several software required to make it possible to program to board which i followed the tutorial in the tutorial resources on the fab academy website.

The code in Git Bash is sensitive even to spaces so if the right code is not working remember to check for unnecessary spaces between the code

After the code is loaded there is a lighting up of both the led for a while indicating that the firmware is uploaded, and i check once in linux to confirm my board was working before i blew my fuses.

I had issues with communicating my board with the programmer, the reason for this issue was that my board were not soldered properly in some parts of the circuit board and also one of the traces were broken off the edge so I had to mill again and it worked the second time.

One of the main issue was our milling machine was quite old so the quality of the board was affected too. And the bits were also breaking quite easily than it would in the new machines.

I made a new board in SRM 20

This board is milled in a brand new SRM 20. We, can clearly see the difference and also it was much easier to solder and I learned the quality of the board also affects the programming, better connections between the pads and the components leads to better and faster programing, also requires less de-bugging.