Hello FPGA lovers! Engineering traditional synth machines using development platforms like Arduino and FPGAs is becoming quite the trend now. Today’s post however takes a twist from the traditional synth machines where sounds are produced by either flicking switches or pressing buttons. The synth machine under discussion is a photosensitive synth machine which uses LDRs interfaced with FPGA in place of button switches and this gives an almost touch screen like feel to the device.
The Hardware required is a FPGA board (adaption may be required), 16 LDRs, 16 high value resistors, a speaker, adequate jumpers and 2 breadboards. The entire project has only 2 sets of hardware implementation off the FPGA board. A speaker is directly wired to the FPGA board besides 16 LDRs which function as the photosensitive keyboard. These LDRs work as a 16 bit Keyboard that inputs signals to the FPGA board to convert to sound signals. The connection diagrams and screen shots are given here.
The coding used for the project has been done in VHDL and the author has given the codes in different modules. The note decoder module on Step 2 is one of the most crucial modules in the whole code as it assigns a particular frequency for the 16 bit value from the LDR keyboard. The sound generator module on Step 4 is the next crucial module as it sends the respective frequency (pitch) values to the speaker interfaced with the FPGA.
Through this link you will find the ucf files for the project. This can be modified according to your convenience in case you would like to add more functionality like sustain buttons and other effects.