Design & Construction

20160305

As prototyping tests of the general purpose core model B are now complete, now would be a good time to take what has been learnt and to try move into the final stage of transferring the design onto PCB.

From this process a modified version of the GPC(b) has been drawn up, here referred to to revision 2. The only real difference is now 47K pull down resistors have been added to all digital I/O lines as to prevent erroneous readings while not in use and a few things have been rearranged. Apart from this it is essentially the same circuit which means that the software created so far should continue to run on a revision 2 board.

 20160306

For the next step a suitable PCB design package needed to be selected and as my budget was very limited a free package was opted for. Many are available on the web but after trying a few I settled on FreePCB, its reasonably striate forward and after experimenting with the features I felt confident enough to try to draw up the new board.

Firstly the size of the board needed to be decided and by quickly looking on Ebay it was found if the cost was going to be reasonable the design needed to be kept to lower then 10cm x 10 cm.

I found a Chines manufacture that would supply PCB's of 10cm x10cm for about £15 plus an additional charge for postage, all that was required was the for me to first create the board layout and to send them the payment plus PCB Gerber files. (standard PCB layout files) 

20160313

The first draft of the GBC(b) Revision 2 PCB #1 has just been completed and a screen shot of the layout is shown below. The package files and payment have just been sent to the manufactures so its now just a matter of waiting to see what turns up.

20160321

The PCB's have just arrived the overall finish is excellent, as the part turn up over the next few days I will be assembling the board performing some basic DC checks to check I haven't made some significant errors.

20160325

The test board has now been populated so testing can begin.

20160401

The uMosbus(s) software has now been rewritten and tested for the new core. The keypad and pulsed output connections have also been replaced with 90 degree connectors to facilitate connection when the LCD is used with the board.

Basic Tests concluded successfully on the new PCB.

Intended modifications for #2 of this PCB.

1 - Very close fit on strip pins, increase hole size to 0.8mm

2 - BT module over hangs A-IO, adjust.

3 - B_Light switch does not indicate which position does what.

4 - The polarisation of the programming port is not clear.

5 - Include a link to bypass potential divider on BT port for TTL connection.

6 - Possibly move keypad port in order to center it on the 16x2 or 16x4 LCD.

7 - Modify transistor placement footprint in order to facilitate assembly.

Links:

Click here to download the associated project files:

- #1 CAM PCB FILES - GPC(b)/RevB - PCB #1 - Tested