Does anyone have a bare bones schematic for this? When I say bare bones, I literally mean that, connections for the USB, VCC, GND, and whatever switching circuitry is needed to be able to use external power (when not connected to USB).
While I can certainly grab the schematic for the Leonardo, that schematic also has a lot of other components on it. I just want to start from the bare minimum and build from there.
You're looking for the datasheet?
That's a good start. What about the barrel connection and switching circuitry?
~~Barrell connector is the top left.~~Why switching circuitry if you wanted minimal design?
Edit: Sorry, this one did not have a barrel connector, just two 0.1" pitch holes for a connector to bring in 5V.
Can you bootload these chips just like an ATmega328? With an Arduino as ISP or USBasp?
Yes you can download a bootloade via ICSP.
The chips also come with a bootloader from Atmel:
"– Optional Boot Code Section with Independent Lock Bits
In-System Programming by On-chip Boot Program
True Read-While-Write Operation
All supplied parts are preprogramed with a default USB bootloader"
What happens if the thing is connected to a computer's USB and you also apply an external 5V to it? There has to be some protection for the USB, no? I want to be able to program it without needing to disconnect its external supply.
Note to Self: Look at current break-out boards like Sparkfun's or Adafruit's.
Neither of those breakouts have a connection for external power, other than the 5V pins which are also tied to VBUS. So, what happens if the thing is connected to a computer AND an external 5V supply? Am I going to have problems with voltage/current feeding back into the USB port? Like I said, I'd like to be able to run the final device from external power with the ability to plug in a USB cable to reprogram without having to disconnect the external supply.
Can I simply put a diode on the VBUS line to prevent the 5V rail to backfeed back into it?
Sorry about the slow response, spent the evening getting rid of a master boot record virus. I was responding to this when it crashed (again) after I thought I had it cleared.
My schematic has a 500mA PTC resettable fuse for USB current source protection.
You can further add a 350mV schottky diode in series to prevent current backflow if desired.
My schematic also shows some headers for jumpers, leave the jumpers off so that Vbus does not connect to +5 or Avcc. Instead connect +5 to Avcc either at the same jumper, or at the external headers.
Do you have a populated product, or do you sell just the board? I'll take one (a pair) off of your hands so I'm not re-inventing the wheel.
Just boards right now. $3 each, send paypal to cardinalflyer @ comcast dot net. Can have in the mail tomorrow for you.
Schematic & suggested PL at Cross Roads Electronics
