INF: Please help extending the information in this page
Refer to Targeted Hardware for hardware that may satisfy these requirements.
The hardware must/should/may ...
- It must have at least one serial interface
It should have at least one JTAG interface
- It must have at least one network interface
- Noise level must be below 20 dB
- It should have over 256MB RAM
- It should have over 512MB Flash for filesystem
- It must have storage interfaces, at least one of them:
It must be able to execute all Freedom Box software at less than half of the CPU load
It should not consume over 15W at full CPU load
- It should be reduced in size, not bigger than a set-top box.
- It must work perfectly between 0-40ºC
Manufacturers should give a minimum of 1 year warranty for a system running 24/7. (Devices that fail sooner are a danger to the reputation of the FreedomBox.)
- The hardware should be as cheap as possible, but not cheaper...
INF: At the first version we do not need to be too ambitious, rugged and harsh environment as well as rechargeable energy powered devices are desired but not at this point
Design of the system
There are many options for supplying power to the Freedom Box. If the aim is to have a 'plug' type enclosure, then a built in supply may be necessary. However, if this is not a hard requirement, a better solution may be to have a 12V power supply 'plug pack' which provides DC power to the device. Inside the device, we would then need smaller, high-efficiency, switch-mode, DCDC converts to provide lower voltage rails.
Power rail requirements
- 1.8V - SoC core is likely to require this.
- 3.3V - some IO may require 3.3V
- 5V - USB requires 5V. 500mA per USB port. If we want to provision for a 2.5" hard drive (or two if we want RAID capability) they will need 5V as well. A typical 4200RPM 2.5" drive uses about 400mW @ 5V, which is about 100mA per drive.
- 12V - Nothing, unless we want to support 3.5" hard drives.
There are many benefits to providing a plug-pack rather than using an internal power supply.
- they are cheap and easily replaceable. internal power supplies are a common point of failure for many devices. There are many examples.
- a plug-pack can provide electrical isolation, making the device more safe. hackers can work inside their device and still be safe.
- heat produced in the plug-pack will not affect the Freedom Box itself.
The rating of the individual power rails, and hence the plug-pack, need to be based around a thorough analysis of the components that will end up being in the Freedom Box itself. This obviously requires further discussion. -- EtienneLeSueur 2012-01-20 05:24:54
The Freedombox will need a lot of components that require continuous power supply at specific low voltages (usually 12V, -12V 5V and -5V). But the main power supply of the box will be with the 50hz oscillation at 220V (in France) from the plug. So we need something to isolate all the hardware from the electric network and give continuous power. (Devices that risk electrocution of the user are a danger to the reputation of the FreedomBox.)
For PC 286 - 386 - 486 and Pentium. the power supply used was the AT power supply. It give + and - 5V, + and - 12V. It is an old one, but maybe easier to use. The switch button is on the electric network side, so it is easy to stop.
Nowadays PC use the ATX technology that give + and - 5V, + and -12V and +3.3V, and the switch button is on the motherboard part so all the system can be turned on and off by software.
Not all of those voltages are essential. It is possible to have components that work only with + and -12V.
Those power supply work well, but they are expensive and not really studied for low power. So it is maybe possible to create our own.
Here is the schematic of an ATX power supply studied for 200W. Maybe we can try to inspire ourself from that.
Such a power supply uses the Switched-mode power supply technique. It is interesting because they are more efficienct (need to be verified at low power) than linear power supply, but they are using an oscillator that will create a lot of noise with a lot of different harmonics that can be very problematic for our use.
Here is a schematic for a very simple linear power supply.
The transformer is to reduce the intensity and to isolate the circuit from the electrical network (especially the ground). A diode bridge converts AC current to DC current and a capacitor produces a stable current.
I don't know if this power supply is stable enough for what we expect, that mean supply component without burn them if there are a jump of current in the electric network.
Maybe that need to be improved before using it.
What still need to be done:
that would be interesting to have a complete modeling of the system with a non ideal transformer, to know what is the efficiency, and what is the component parameter that we need. Especially for the transformer and the capacitor.
We can add some other component to make some filter to increase the stability of the system.
Maybe it can help to add an other transformer and diode bridge in the linear system. And add signals with a Pi/2 dephase difference (just before the capacitor) to increase the total efficiency.
This part takes the signal from the plug and divides it to the different part. Maybe it is useful to use a transformer to isolate the electric system.
It is a filter which need to have a good bandwidth and a frequency controlled by the processor