| Name | Modified | Size | Downloads / Week |
|---|---|---|---|
| Documentation | 2024-01-30 | ||
| Csharp8toC9 | 2024-01-28 | ||
| A7toGsharp8 | 2024-01-28 | ||
| README.txt | 2024-01-28 | 2.3 kB | |
| Totals: 4 Items | 2.3 kB | 4 |
A Top Octave Generator ====================== Simultaneously generates an octave of 12 notes. The folders A7toGsharp8 and Csharp8toC9 contain slightly different versions, emulating two TOG IC frequency ranges. In the 1970s, electronic instruments were made that used a Top Octave Generator (TOG) IC. Almost all of the TOGs took an input frequency derived from a 2.00024 MHz oscillator circuit and provided twelve or thirteen square waves of the right pitches by dividing this input frequency by factors from 239 to 478. This provided square waves with frequencies between 4434 and 8368 Hz. Lower frequencies for the instrument were generated by dividing each output through counter ICs, providing each input frequency divided by a power of 2. People repairing these instruments can source suitable divider ICs, but the TOG ICs are no longer made. Custom chips or old stock are available, but are expensive. An alternate is to provide a software solution for a cheap microcomputer. The software presented here is for an ATmega328P with a 16MHz instruction clock. In this implementation the notes are generated as square waves, with the length of the on/off periods varied in increments of 500ns. Because the note periods are not exact multiples of 500ns, an algorithm increases some periods by 500ns to bring the average closer to the true note. The highest note generated is C9 (8,372Hz) with the periods varying between 119 and 120 500ns periods. It is hoped this variation is inaudible. Two almost identical sources and .hex files are provided. The original software was written to emulate a Mostek MK50242 with a 2.00024 MHz clock, generating the octave C#8 (4435Hz) to C9 (8372Hz). This is in folder Csharp8toC9. The second set of files, in folder A7toGsharp8, was developed specifically for the Lyrebird Recreation Project. This specified a Top Octave Generator IC AY-1-1012 with an input clock of 1,587,520 Hz. There doesn't seem to be data on the AY-1-1012, this may be a typographical error. There is an IC AY-1-0212. From the circuit of the original Lyrebird Piano circuit it appears the IC is logically equivalent to to the MK50242 but clocked at a lower frequency. Additional documentation is provided in the folder Documentation.
