The Mini-ITX board (Phase 2)
The complete machine will fit on a Mini-ITX board, to sit in a PC case. It will only be designed once the validation board has been proven.
The form factor
- 170 × 170 mm, the Mini-ITX form factor;
- a 4-layer board: signal, ground, power, signal;
- 4 mounting holes of 3.96 mm, spaced about 154.94 × 157.48 mm apart.
The layout
- Rear edge (left to right): the Tang Nano 20K with its flush HDMI socket, three USB-A blocks, the microSD reader, the output and input jacks, the double DE-9.
- Centre: the processor, the 9K and the PSRAM, grouped so that the bus traces are short.
- Left edge: the expansion port and its buffers.
- Right edge: the 24-pin ATX connector and power management.
- Front edge: HD Audio, reset, LEDs, front-panel USB, front-panel connector.
The system controller’s FPGA is soldered on the board. The modules (Tang Nano 20K, Pico) are mounted on female headers, and the processor in a socket: they can be removed.
Power
- An ATX power supply or a picoPSU, of which only the 3.3 V and 5 V are used (no −12 V).
- 5 V budget: about 4.5 A (7 USB ports at 500 mA, plus the logic).
- The Tang Nano 20K through its 5 V input, the 9K’s FPGA through the 3.3 V rail and its 1.2 V and 1.8 V regulators, the Pico through VSYS via a Schottky diode, the processor and the PSRAM from the ATX 3.3 V.
- A small ATtiny202 microcontroller, powered by the 5 V standby, handles power on and off (PS_ON signal); as long as the supply is not stable (PWR_OK), the processor stays in reset.
Bill of materials and budget
| Component | Quantity | Indicative price |
|---|---|---|
| W65C816S | 1 | €10 – 15 |
| PSRAM APS6404L (8 MB, QSPI) | 2 | ≈ €8 |
| GW1NR-LV9QN88P FPGA, 1.2 V regulator and 27 MHz crystal | 1 | €25 – 30 |
| Tang Nano 20K | 1 | €25 – 30 |
| Pico 2 W | 1 | €7 – 8 |
| FE2.1 hub and 7 fuses | 1 | €3 – 5 |
| TLV320AIC3254 codec and TPS7A20 regulator | 1 | €7 – 9 |
| DS3231 clock and battery holder | 1 | €2 – 6 |
| 74LVC245 | 2 | €1 |
| ATtiny202 | 1 | €1 |
| Connectors (USB, SD, jacks, DE-9, ATX, headers) | lot | €20 – 30 |
| Passives, LEDs, button, crystal | lot | €8 – 12 |
Parts will be chosen, where possible, from the LCSC catalogue, for surface-mount assembly by JLCPCB: some packages (QFN) are impossible to solder by hand. The availability of the FE2.1 and the TLV320AIC3254 remains to be checked.
Budget for the complete machine: €250 to 450, including the printed circuit board, case and power supply.