<seo title="Wiki Diskio Pi" metakeywords="daughter,board,carte,fille,diskio" metadescription="Diskio Pi, a touch device compatible Raspberry Pi, Odroid XU4 C1+ C2" google-site-verification="QxITLFv-iwiUVf0_k9CyECyacMJUQiDQuKnpB59Nu9w" />
All the informations about the daughter board (and the button board) are here! The detailed version here is the revision 0.1 of Diskio Pi 0.3, studied in spring 2018 following the first funding Ulule. Other versions will be gradually detailed.
The daughter board v0.1
- Step-down module (buck)
Thanks to the online tool Texas Instruments WEBENCH®, it was relatively easy to find a design corresponding to the board's needs: input between 7.5V and 12V, output 5.4V to 4A. Some thermal simulations allowed to choose the right input voltage, and the right chip for this function. In the end for this version, an input voltage of 9V to 3A, and an LM3150 controller were chosen.
- advantages: no or very little heating
- disadvantages: 9V 3A is not standard: use in a car or boat requires the implementation of a front power supply (12V to 9V), and the AC/DC power supply unit is slightly more expensive.
- USB 2.0 Hub
Chip used: GL850G. Designed in Taiwan, this chip equips the HUB of the Diskio Pi 0.2, under the brand name D-Link®. The tests performed under different OSes all worked, the powered HUB function being essential for use with an SBC. As the production of this chip is still active, the risk of rupture is very low in the coming years. Moreover, the design of this chip being quite old, the prices charged are very reasonable. For the design of the circuit, there are online diagrams that can be adapted. (example1, example2)
The only function to be designed is the double USB input with automatic selection, which can be realized with a transistor and some components. It seemed useless to us to make the HUB programmable, the standard EEPROM being the most widespread use.
This function prevents the voltage peak at start-up. During the boot of the SBC, if the screen turns on at the same time, there is a voltage drop that can create problems (no boot). The solution is therefore to delay the SBC power-up by about 3s compared to the screen start. Chip used: LMC555CMX
- MOFSET switch and control LEDs
Automatic switch that cuts off the 5V (works a bit like a relay, but totally silent). Controlled by the timer, this function has been prototyped using the module Pololu PSW04B. The addition of control LEDs allows you to see the action of the timer + switch.
- Fan management
Already studied for Diskio Pi 0.2, we use here an LM311 comparator which reacts according to two input voltages, the first being 5V and the second being modulated by the probe (KTY/121). This dial indicator will trigger whether or not the fan is switched on. A potentiometer allows the adjustment of the fan activation temperature.
- ON/OFF/ON switch management
As the manual switch is on an independent card, a circuit has been designed to manage a very low current through the connection cable between these two cards.
- HDMI routing
Simple independent routing, which connects a female HDMI port to an internal port compatible with a 20-pin ribbon cable.
The main functions of the board are briefly explained in this diagram:
The voltage of 5.4V is desired to keep a minimum of 5V when the Pi is loaded and the screen is on, so that the SBC does not unexpectedly reboot. All SBC boards support this slight overvoltage very well, as well as the HUB chip.
All dimensions are in mm.
Originally named motherboard, its name has changed, as well as its version number.
List of components (BOM)
What remains to be done (TODO)
- USB input selector switch
- Adding a 5V output power capacitor (added by hand, not shown on Gerber v0.1)
- 3.3V SBC detection to allow automatic fan shutdown in case of shutdown (the board remains powered)
- Addition of micro-fuses at the fan voltage output / SBC / display
The button is a slide switch with 3 positions: on - off - on
- position 0 : display only ON
- position 1: OFF
- position 2: screen + SBC ON
This (very thin) cable accepts a maximum current of 700 mA, so switching from 9V3A is impossible. It was therefore necessary to design a circuit on the daughter board with a few diodes and transistors to manage the input voltage.