The OSSC does not output audio over HDMI or DVI-D, respectively. This add on captures the analoge audio you feed over the SCART or audio 3.5mm stereo jack. The audio signal is digitalize and put into the IT6613E over the I2S audio interface. This repository provides the hardware design for the modification. The installation requires installation effort which depends on the OSSC version number you have. Firmware ======== The IT6613E has to be programmed appropriately to insert audio to the digital video output. In the 'original' firmware audio is not taken into account. Therefore the firmware of the OSSC has to be updated. Up to the OSSC firmware version v0.73 you can grab the current firmware in this repository. With v0.74 the source code part needed for the audio modification was integrated to the official GitHub branch by marqs85. The builds can be grabbed from the official source: https://www.niksula.hut.fi/~mhiienka/ossc/fw/. Additionally, I provide a mirror here. PCB Production ============== Choose the service you would ever like. I have uploaded the design to OSHPark, too. VERY IMPORTANT: The substrate thickness has to be as thin as possible. The PCB for v1.3 is design to sit between lifted pins of the IT6613 (the HDMI transmitter) and OSSC-PCB (just look at the installation pictures to get an idea ;)). With v1.5 the OSSC comes with jumpers which are connected to the appropriate pins of the IT6613E. The add-on sits on top of the jumpers (don't forget to open them). I have produced the PCBs with OSHPark and have chosen 0.8mm thickness. The PCB must not be thicker. Link to PCB at OSHPark: - https://oshpark.com/shared_projects/rmFBAKyo (for v1.3) - https://oshpark.com/shared_projects/vKUEgBSy (for v1.5) - https://oshpark.com/shared_projects/WeKdeoGP (for v1.5 with wired connection to the SCART) Part list of the DIY-Audio PCB ============================== running number ------ footprint(s) --------- device/part --------- package ----- mouser ordering key 01 | U1 | PCM1808 | TSSOP14 | 595-PCM1808PWR 02 | U2 | 74LVC1G34 | SOT23-5 | 595-SN74LVC1G34DCKR 03 | U3 | MK2705SLF | SOIC8 | 972-MK2705SLF 04 | FB1, FB2 | Ferrit Beat | SMD0603 | 81-BLM18PG471SN1D 05 | C1 | tantal-cap. 47uF/16V | SMD case C | 74-293D476X9016C2TE3 06 | R11, R12 | res. >2.2 kOhm | SMD0603 | 71-CRCW06034K99FKEAH (e.g. 4.99k) 07 | C11, C13, C15 | tantal-cap. 10uF/6.3V | SMD case A | 74-TR3A106M6R3C1500 08 | C12, C14, C16, C21 | cap. 0.1uF/50V | SMD0603 | 77-VJ0603V104MXACBC 09 | C17, C18, C31 | tantal-cap. 1uF/16V | SMD case A | 74-293D105X9016A2TE3 10 | R19, R20 | res. *** | SMD0603 | see description below 11 | C19, C20 | cap. *** | SMD0603 | see description below 12 | R31 | res. 33 Ohm | SMD0603 | 71-CRCW060333R0FKEAH 13 | C32, C33 | cap. 0.01uF/50V | SMD0603 | 77-VJ0603Y103KXACBC RC-filtering of the Audio ========================= The RC filters (R19,C19) and (R20,C20) mainly bandlimits the noise. The filter also avoids aliasing effects if the bandwith of the audio signal increases. The PCM1808 samples the audio signal with 96kHz. This means that the cut-off frequency of the filters have to be 96kHz or below. The firmware will also allows you to further downsample the datastream to 48kHz. If you want to use that I recommend you to set the filter to 48kHz or below to avoid aliasing. The cut-off frequency f_c of a simple RC low pass filter is determined by f_c = 1/(2*pi*R*C). here is my choice which gives a cut-off frequency of 47.938kHz. 10 | R19, R20 | res. 3.32 kOhm | SMD0603 | 71-CRCW0603-3.32K-E3 11 | C19, C20 | cap. 1000pF/50V | SMD0603 | 77-VJ0603Y102KXACBC PCB-Installation ================ See folder installation ;) For providing pictures, thank you to - Kharmeleon (user from Circuit-Board.de) - Kabloui (user/customer from VGP)