Programming Arduino Mini’s and similar units with no on-board USB requires a USB/RS232 adaptor for the computer (unless you really have a RS232 port on your PC, then you need a MAX232 Level Translator)
I scoured eBay to find the cheapest converter, and i found this.
Looking a bit further, for a bit more you can get this that is housed in a nice case [link]
These units use the CP2102 USB to TTL converter chip [Datasheet]
Funnily enough, the RST pin is brought out, this pin, when taken low will make the CP2102 go into low power mode and de-enumerate. You can wake up a computer in sleep mode by toggling this pin.
But i do not need to do this, i’m more interested in using this for programming Arduino’s.
Arduino’s use the DTR pin for the reset of the bootloader, and this pin is fortunately at the very corner of the QFN chip so it’s easy to get to.
Removing the pullup resistor [R2] and soldering a small wire from the DTR pin to the RST pin brings out the DTR pin for Arduino programming.
I cut the original trace for the RST pin on the underside of the PCB, but i was too lazy to take a picture of that.
When i was modifying the unit i replaced the header pins too, since they looked like they were soldered on the wrong way round, they don’t really fit in the cutout of the case…
Some pics of the modification:
