USBasp is a USB in-circuit programmer for Atmel AVR controllers. It consists of an ATMega48 and a couple of passive components. The programmer uses a firmware-only USB driver, no special USB controller is needed.
This variant is for 3.3V circuitry.

Programmer and additional socket board for varies AVRs are shown on the picture.

Optional socket board schematic is included in download archive.

This schematic is a bit simplified from original one. Differences are: used here ATMega48 must be initially programmed via another programmer, for example with PonyProg2000 because there is no connection between RESET and SS; only ATMega48 (not ATMega8) can be used as it works with 3.3V power supply and 12MHz. Future serial interface is not implemented and will not work at all because there are connections with RXD, TXD and ISP connector. Pin layout of ISP connector on socket board is different from one specified by ATMEL.

- USB_programmer.sch, USB_programmer.pcb, USB_programmer_extension.sch, USB_programmer_extension.pcb - circuits and board layouts for programmer itself and optional socket board.
- usbasp.atmega48.2009-02-28.hex - firmware. Upload it into ATMega48 with another programmer.
- win-driver - folder with USB drivers for Windows. Specify it when prompted (after you plug USB cable into computer).
- eXtreme Burner - AVR - GUI program for loading HEX files (firmware) into AVR microcontroller.

Download link.
Link to free ExpressPCB software to be able to open .pcb and .sch files.