Thursday, 28 November 2013

Birth of a Bitfrore

Building a Bitfrore

I recently built another Bitfrore prototype so I thought I'd take the opportunity to capture the whole process from start to finish.

The prototypes are completely hand built so its a process that anyone could use to develop their own electronics at home.

I use the toner transfer method for etching my homemade PCBs. This process allows a very fast turn around between design and testing.

The first step is to print the PCB layout onto thin glossy paper. I used a page from a winter sports catalog.

Next I position a blank PCB onto the print out and secure it in place with tape.

Using a Hot Iron with the steam switched off the printout can be transferred onto the PCB.
The PCB and transfer is upside down in the image above. To perform the transfer you should iron the paper directly. You need to apply enough pressure to perform the transfer but not too much that it will smear the fine traces on the PCB.

After 45 seconds of ironing the hot PCB is placed in the water bath. The thin paper will absorb the water and become easy to peel off. 

Most of the paper can be peeled away by hand revelaing the transferred PCB layout.

Using an old toothbrush the rest of the paper can be cleaned off.

Due to the inaccurate nature of the transfer process its necessary to check every trace with a magnifying lens and ensure that each trace is separated.

In my design the traces are 0.4064mm on most of the board 0.254mm when leading into the microcontroller.

Its much easier to scratch away toner now than it is to scratch away copper after etching. If any traces are incomplete a Sharpie can be used to fill in any minor gaps.

It may be necessary to completely clean off the toner with Acetone and start again if there are any major issues with the transfer.

The next stage is to etch away the copper not covered by toner.
The chemicals used in etching are highly toxic and must be handled carfully. Be sure to wear protective gloves and glasses and work in a well ventilated area.

After etching the etchant solution must be disposed of correctly. You cannot simply pour it down the drain.

Slowly the etchant will eat away at the copper as you can see here on the left side of the board.

After 10 minutes the board is fully etched and can be rinsed clean and dried.

Now the transferred toner needs to be removed to reveal the copper beneath,
I use nail varnish remover that contains Acetone and paper towels.

 After cleaning the copper traces and solder pads are revealed

Its now important to check for any shorts on the board caused by imcomplete etchig. Its much easier to break any bridges now as a short could easily be hidden under another component after soldering.

The next stage is drilling. I use a Dremel mounted in a small bench press.

Due to the surface mount design I only need to drill holes for the printer connecter,control panel,DC jack and mounting screws.
Now we can begin soldering. I always start with the microncontroller and programming port. This enables me to check the basic functionality of the board.

I carefully check each pin on the microcontroller for shorts using a multimeter and clean up any shorts with solder wick.

I then add the header pins for the programming port and attach a programmer to verify the board is functional. At this point the chip is powered by the programmer.

After loading the chip with the bitfrore software I can start adding the rest of the components starting with the power supply.
Then the randon mumber generator.
And finally the transistors to control the printer. The PCB is now completed.

The next stage is to build the control panel. I just used a piece of protoboard to mount the button and led.

Next I mount the printer and connect the control panel.

Finally we're ready for a complete test.
This printer includes a special bonus feature that also needs to be tested.


And just like that a Bitfrore is born.

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