Friday, January 9, 2015

Current Limiting Power Supplies Are Your Friend

Tonight I made an ICSP cable to program the two PIC chips on the PCB for the first time. Powering the board caused the power supply to go to constant current mode (yay me for setting it really low). I found that the 7805 regulator and PIC16F88 got super hot, so the PIC16F88 is probably shorted. I cut the ground pin (red arrow) and saw the current drop to normal levels.


I actually don't have any spare so I can't get it running just yet, but i was able to program the main mcu without any problems :)

Monday, August 18, 2014

Good News!

I get another opportunity to do more PCB design!
Good news everyone!
I picked up my PCBs today and I am super excited! But I did find an error that might just make them unusable. Getting it right the first time obviously would have been a lot better, but hey, shit happens.
There's actually two problems. The first being that I completely missed the USART pin header. As in I never put down the pads or traces! No idea how that one happened. Maybe I should have some sort of documentation or checklist to ensure I meet my own specification. I could probably get around this omission by soldering the required connections directly to the microcontroller pins.

The second problem is where i'm stuck. Seems I got the pads wrong for the multilock connector at the top of the board. The holes are just too small. I could drill out the holes to be bigger, but I don't think it's going to turn out well with a 1mm drill bit on a hand drill.

I'd like to hear if anyone has any ideas on how to fix this. Otherwise it's not too bad to do another run of PCBs. For now it's back to uni work :)


Tuesday, August 5, 2014

PCBs and feature creep

Hello to my readers, all 6 of you. Seems like this update took even longer than usual!

Circuit Boards
I've finished the circuit board design and sent it for manufacturing at . They do small runs, 10 boards instead of hundreds, which is perfect for what I need.
This is my first ever PCB, so if you know something about PCB design and have suggestions for improvements I'd really like to hear them! It's a 4 layer board with the 2 middle layers as power planes. I did learn quite a bit while doing this, so i'm pretty happy with that. The design process is basically this:
1. Draw up your schematic diagram
2. Associate each component with a footprint. A footprint is the collection of metal pads that match up with all the pins of the component.
3. Arrange the components on the board and make the appropriate connections.