ATX power supply led indicator and a simple circuit to test the output voltage of the LEDs, you know the observations made with the sprint pcb layout (.lay) located in drawing on the source site also has plenty of high-frequency transceiver circuits
Simple ATX Power Supply Tester
ATX Power Supply Tester Circuit schematic PCB files download:
ATX Power Supply Tester Circuit ZIP File Password: 320volt.com
LED Bar Indicator Audio Spectrum Analyzer Circuit
Opamp and cmos integrated circuits based on sound level indicator audio spectrum analyzer circuit led bar display used 10 pieces for a little advanced version of the classic spectrum analyzer, VU meter circuit circuit circuit diagram a bit complicated but it is written makes it easy for you to work more or less pcb drawings
Audio Spectrum Analyzer Project