The author modified a vintage Casio PT-10 toy keyboard to add programmable synthesizer capabilities by enabling the ADSR voice feature that was present in the related Casio VL-1 but omitted from the PT-10. Using the PT-10 service manual and VL-1 documentation, they made surgical modifications to the PCB by cutting traces and adding jumper headers to access calculator mode for programming custom voices with eight-digit codes that control envelope, vibrato, and tremolo.