I’ve designed another PCB This time it’s a simple undershield for the Arduino pro mini. I received the PCB’s from Electrodragon (12$ for 10PCB’s) last week. The PCB has a Schottky diode and a 5V linear regulator, I’m using an LM2940 5V regulator. For the rest there are just 2 rows of female headers to plug the pro mini in and 3 rows of male pins on each side.
The reason I’ve had this PCB made is that pro mini’s are dirt cheap these days, you can find them on Ebay or Chinese shops for less then 4$. That makes them the cheapest Arduino on the internet. It’s cheaper and easier to buy a pro mini and integrate it in to your own project then to design your own PCB with an ATmega328.
The pro mini on its own is not very usable in projects. They were designed to plug in to a breadboard. With this undershield they are lot more usable. The pro mini only has a tiny 5V regulator, you can’t draw much current from it before it goes up in smoke. By using the undershield the pro mini is powered through the Vin pin, via a Schottky diode. The rows of 5V pins are powered from the LM2940 regulator.
BTW the pro mini does not have an USB to serial chip. So you need to have USB to serial cable to upload sketches to the pro mini. I use an FTDI cable. I’ve bought several pro mini’s on Ebay and none had a bootloader on them. Thankfully I have an USBasp to upload the bootloader via ISP. So you’ve been warned