I can connect to my AVR circuit with AVRISP, but PSI-ISP or AVRUSB or AVRISP-U cannot find the target device. What is the problem?
PSI-ISP (plus AVRUSB and Keyfob and Handheld Programmers) have more protection against faulty circuits. For this reason, they need your target circuit to conform to Atmel's recommended ISP specification. Circuit details can be found in Guide to AVR ISP Circuits