Jan 222012

So, I got my boards back, got the components ordered in, and I’ve assembled a couple of them.

They don’t work.

Kinda. The micro runs whatever code I put on there, the LED’s blink if I tell them to, but it doesn’t like the USB part. I plug it in, and my computer chucks a dummy spit saying that the “USB device is not recognised, bro”.

I got it working on the breadboard, the exact same code. And apart from a few extra LED’s (that aren’t currently turned on), there’s not much more to the circuit. I have verified all traces, all paths, checked for any bridges, etc. I just don’t know what’s going on.

I’m posting this up to see if anyone can help me debug the sucker and maybe tell me what’s going on. I’m including the schematic, the board layout, the eagle files and a high-rez photo of the current state of the board.

Note, since this board is Rev1, I know I screwed up a couple of things. Most importantly, the 1.5k resistor, R5, should have been connected to the D- instead of D+, that’s been fixed by soldering R5 directly to the “correct” place. Also, the ISCP header, I’ve mislabelled GND/VCC (I know, I know!), so on the board it’s crossed out (but the pins are in the correct spot). I’ve put 22pF capacitors for the crystal instead of 18pF as a different test (this is the second board I assembled to rule out “burnt component” issues).

Here’s the deal. If you are able to point out what I’ve done wrong, I’ll send you one of my blank PCB’s.


Board layout:

Populated board (no switches):

Eagle Files:


Jan 132012

My boards are here!!

This is going to be a “utility keyboard” – uKB.
4 buttons and one rotatory encoder, plus 6 PWM’d LED’s. All inside a nice bamboo box. It implements standard USB HID, so it should be plug&play on all computers. You have ISP header for the atmega328p, for changing firmware, and I’ve brought out all spare pins to a spare space on the lower right.

The thing is, the boards arrived on a friday afternoon, and i wasn’t expecting them until monday, so I don’t actually have the components to populate the board! I guess that will have to wait until next week!

Jan 082012

I’ve been thinking about creating my own LiPo charger for a while now. Something that will allow me to charge a large array of LiPos in the field without it been fiddly or annoying.

Since I now know a bit about electronics, I set out to see what it would take to make a simple and modular single-cell LiPo charger. Something based around the MAX1555 or the MCP73831. I chose the Microchip one because I liked the fact that the datasheet had a recommended layout for the PCB tracks to improve the thermal properties.

For the daisy-chaining, I’m using these cool hermaphroditic connectors from TE. They handle up to 6A, so it should be good for a few chargers in one chain. And they’re only 79c!

For regulation, I’m using a Murata switching regulator to get from Xvolts (where X can be a car battery) to the 5V the lipo charger chip likes (thanks Kean for the suggestion!). They’re not terribly cheap, but they’re efficient and kinda small.

I’ve also put on one end a USB socket to allow charging of a single battery off USB. There a lot to be improved in that corner, and I don’t think it’ll be the primary usage, but in a pinch it could be very handy. Since USB only allows 100mA draw without negotiation, I’ve laid out an ATTINY there to act as a USB device that wants more power. There’s a lots of suggestions flying around, like, put a fuse there (Madox, Jaye), and they’re all good ideas, but I haven’t gotten around to implementing that yet.

All of this experimental, of course, but this is the fun part!


Board Layout:

Download the EagleCAD files here: MCP7383_v1