Posted on

Graham’s Status Report for 3/26/22

This week, I finished the Front Panel design and am in contact with Ed Wojciechowski to facilitate water jet cutting. This will be simple and cheap hopefully. I sourced the MIDI input board and ethernet coupler for our rear panel. We still need audio jacks, DCin and power switch. I think we can simply find those around. We have to figure out this AXI interface and protocols soon so we can finally communicate with the FPGA modules. We should produce the MVP in the next two weeks, including bare minimum oscillators, integrated MIDI, and a few encoders.

We are definitely behind schedule. I believe we should have had the MVP ready by now based on our gantt chart. However, in hindsight, this goal was a bit ambitious. I am confident we will be viable by next weekend! In order to achieve this I will be more realistic with our goals and put maximum effort into all the elements of the MVP in the coming week.

Posted on

Sam’s Status Report for 3/19/22

Last week I wanted to finish the power supply section (only the 3.3v rails are done, need to add low noise 5V regulators too) and to get a solid plan for the front panel interface. I accomplished both of these, which technically puts me on schedule. The positive and negative 5V rails are used for the analog path (VCF and VCA both require split rails) and the 3.3V is for logic, FPGA, encoders, etc. We solidified the plan for front panel interface including number and function of rotary encoders. I ordered all the front panel stuff, including knobs, encoders, and quadrature to I2C PCBs. Each encoder will have a small PCB behind it to count the quadrature pulses and put all of them on the same I2C bus which we will be able to poll with the SoC.

Next week, I want to make significant progress in PCB layout. The schematic is becoming more firm and I can start to do actual layout soon. At a minimum, I would like to start the analog path layout next week.

Posted on

Sam’s Status Report for 2/26/22

This week, I completed the analog path schematic design which was the goal I stated last week. As a group, we decided to change the synthesizer architecture to be duophonic rather than polyphonic, so there are two VCFs and VCAs with independent control signals. I added ample power supply decoupling and RF chokes to separate the analog and digital supplies.  There is a high speed I2S DAC for audio which has two channels (right, left) followed by two VCFs with both adjustable cutoff frequency and resonance, then two VCAs. The output of the VCAs is buffered with opamps and an 8-channel I2C DAC is used to generate the control signals which drive VCFs and VCAs.

Completing this puts me perfectly on schedule, which is great. For next week, I want to finish the power supply section (only the 3.3v rails are done, need to add low noise 5V regulators too) and get a solid plan for the front panel interface. This includes ordering the correct number of potentiometers, rotary encoders, and knobs as well as starting the schematic design.