I’ve done some circuit work before, but always on a breadboard or sometimes a perf board. This time, I’ve got enough components that I need a (2 layer) PCB to keep everything sane. I’ve used Eagle and followed all of the suggestions I could find online.
Project: I’ve got an 8-input A/V switch with 8 buttons, but no remote. I’ve traced out its internals, and I know that the buttons all connect to an epoxy-blob IC inside, and will short pin 23 to 25 through 28 (buttons 1 to 4) and pin 24 to 25 through 28 (buttons 5 to 8) when pressed. So I’ve got an Arduino with an IR sensor. Eight of its digital output pins feed the base of a transistor through a (1Mohm) resistor, causing the base/emitter to connect the appropriate pins. This much I have breadboard-ed out, with the Arduino board, and confirmed as working.
Everything’s through-hole. I plan to put a socket on the board, and the atmega into that. The IR data/vcc/gnd pins feed that sensor, and the P23 to P28 connect to the chip in the A/V switch. I plan on doing an input mode/write high in the Arduino to set the unused pins’ pullup transistors.
Here’s all the relevant files; you should be able to download (in the file menu) the whole zip, or (with the drop-down arrow on the right) any specific file.
When you say “100n” you mean 100 nano-farad capacitor, right? I suppose I’ll leave AREF floating if that’s OK.
And I forgot to mention: my vcc and gnd will be tapped from a voltage regulator already inside the device I’m modding, but the decoupling caps should be an easy addition. But if I’m supposed to put 2 caps, where exactly do they go?
How do I know what “too large” is for the base resistors? I’ve tested this value and it appears to work. Any current I put into the base will flow out the emitter, right? I don’t know much about the existing circuit so I don’t want to add more than is necessary.
Programming header: I don’t expect to be changing this much, so I’ll socket the atmega back into my arduino board if that’s really necessary.
I specifically chose a barrel crystal ( http://goo.gl/bNEx3 ) to squeeze it in, but I should be able to give it some more breathing room.
Mounting is just going to be hot glue (with something to act as an insulator where necessary); again, this is going inside an existing device, I don’t have anything to screw to.
The “5v” has been moved, I rearranged those pads to shrink the board a little and missed that, thanks!
I’ll try to work this all into the design and reply back with the updated version.
I think this takes all your input into account. Didn’t move the crystal (yet?) – there’s not as much room as I thought, I’ll take a harder look at the physical components and judge if I need more room there or not.
