This uHat is designed to plug on top of a pi0 or pi0-w. It's designed to plug to the DIN-5 at the back of a Minitel-2. The pi0 will be powered by the Minitel through the Buck converter on the hat. TX and RX will be level-shifted to the right level on the pi's UART.
The aim is to plug the resulting dongle into a Minitel, and get instant linux.
3615 pi0 (or shall we say, 31415 Minitel).
- https://niteshbharadwaj.github.io/posts/raspi_from_battery.html
- http://pila.fr/wordpress/?p=361
- http://www.jelora.fr/post/2020/02/25/Adaptateur-prise-DIN-peri-informatique-Minitel-vers-Serie-RS232-et-Serie-USB.html
- https://www.ti.com/lit/ds/symlink/lm2596.pdf
- https://www.edn.com/pcb-layout-tips-for-thermal-vias/
- https://www.instructables.com/id/Arduino-to-RPi-three-ways-to-convert-5-volts-to-33/
- https://randomnerdtutorials.com/how-to-level-shift-5v-to-3-3v/
- Cin and Cout
- should both have short leads to lm2596
- should both have low ESR (e.g. high V rating, Nichicon PL, 1.25*Vin = 10V)
- Ripple current rating 50% of DC load (500mA in our case)
- Cin 270uF or 330uF
- Cout 470/25 Pana or 560/16 Nichi
- Diode
- current rating = 1.3*load = 800mA
- reverse V rating = 1.25*Vinmax = 10V
- Heat pad should at least be 0.4"²
- L choice see page 20 of Datasheet
- L21/L22
| uH | A | SCHOTT | SCHOTT | RENCO | RENCO | PULSE | PULSE | COILCRAFT | |
|---|---|---|---|---|---|---|---|---|---|
| L21 | 68 | 0.99 | 67144070 | 67144450 | RL-5471-5 | RL1500-68 | PE-53821 | PE-53821-S | DO3316-683 |
| L22 | 47 | 1.17 | 67144080 | 67144460 | RL-5471-6 | — | PE-53822 | PE-53822-S | DO3316-47 |
- If we want low output ripple we can add post ripple filter 1uH-5uH with low DC Resistance and low ESR cap