Raspberry Pi has been nearly anywhere – robots, desktop computers, laptops, control centers, HTPCs, control centers, game machines, bar tables, spy devices, web cameras – to be continued. But what about a wearable computer? Something I dream about? I haven’t seen some project that went public yet. Basically, nothing to be inspired from, than Pip-Boy =)
And that’s OK, as long as the idea inspires me enough to write about it. Talking about Pip-Boy – that’s kinda of what I want my future wearable PC to look like. I want it to be placed the same way – on my arm, but I won’t be making it as big as Pip-Boy yet =) It has to have two 18650 cells inside, with the way to charge them. It also needs to have BT and USB hub inside, and, possibly, WiFi. I want it to be wireless yet reliable so some crucial communications will be wired. Talking about communications…
What could this PC have as a display? There’s no such a thing as “cheap yet good display for RPi”. SPI screens are slow to refresh. Composite video screens don’t have any much quality of image, also, the resolution is limited. HDMI screens are expensive and hard to find. Those DSI-connected screens simply do not exist. Given that my money is limited, I’ll now have to choose between composite video and SPI… And at the moment I choose neither. I think I can live without a screen for a while =) I had an old idea of hanging three Nokia 3310 screens to the SPI port of either RPi or Arduino as a helper module. I still have it and I like it – there is a place for them on my sketch I have in mind. They’d be showing time, date, status of various wearable PC additions and possibly would have some controls to make a simple menu using them. This is much more easier and less expensive, even though requires some soldering 😉
So – what’s RPi lacking from a perfect wearable PC base? Well, Model B with its 512MB of RAM seems good, but…
Small size and energy consumption seem to be the problem. What’s about size?
Even though we can’t change the board’s length or width, we can change height. There are some connectors that can easily be removed, and we can use pins to connect something to RPI instead. For example, we could replace the double USB connector with 2 groups of 4 pins – both replacing each 4 contacts of each one of two USB ports. For RCA jack, there’s only two pins. For audio – 5, but it seems that 2 of them are useless, so let’s say – 3. Ethernet jack? Well, I suppose I don’t really need Ethernet on my wearable computer, MB I could bring USB-Ethernet card with me just in case, but that seems an overkill even for debugging. So Ethernet jack stays somewhere else in my drawer 😉 I won’t be removing neither HDMI not CSI/DSI as they’re OK and don’t enlarge size that much, also, they will be used sometimes.
OK, something is clear about the size. What about the energy consumption? Well, there are three things on the board that consume energy.
First is the CPU. We can’t do much about it, though, except underclocking. The best we can do is to cool it down. I think heatsink really has to be in my wearable computer – just for the stability 😉 So – I’ll have to have a heatsink on CPU. I’m not sure how this will improve power consumption, though, but it will definitely make a job easier for the CPU. Second is USB hub&USB-Ethernet chip. Well, I personally think we can remove it without a doubt. Why? First of all, it’s laggy sometimes, some users still report driver problems regarding exactly USB-Ethernet, as I’ve seen on forums. Also, I won’t be needing Ethernet, remember? So I think it’s better to have the possibility of choosing whether I want USB hub enabled or not, and thus have better power management. You see, you can turn off external hub – but with internal it’s not that easy. Also, it freakin’ heats up =) So – I’ll also have to remove this SMSC chip. Third part is 5V-3.3V regulator. It’s linear, so it heats up, too. Also, I think I’ll need much more current on 3.3V line than this regulator can provide, so I think I’ll be replacing it with something else. Some guys did replace it with a switching regulator, I think I’ll do the same.
So – remove the linear regulator.
Also, speaking about the power – will have to think about whether this MicroUSB port with the corresponding capacitor and fuse are really necessary. Given that I’m likely to power everything through GPIO header, I think they aren’t.
Okay, I can now imagine the board without all those large connectors. The only things that remain are: GPIO headers, USB/audio/RCA headers, reset header, HDMI/CSI/DSI connectors and the CPU. It just seems like an Arduino now, having some pins we can plug a shield onto. And we will. I think that RPi is to be like a processor shield for my wearable computer, and we have to plug this processor shield into an expansion board. What’s this expansion board? First of all, something that will be connected to all the GPIO pins of the RPI. So – in the base there must be a PCB with sockets for GPIO pins and stuff. It should expose USB/RCA/audio connections, too. Then, we have to have some kind of USB hub there. I think it won’t be hard to make a hub directly on this PCB.
Like, we have chips like GL805, which have accessible specifications, and they don’t require that much of components to work, and what’s most important – they’re in every second Chinese USB hub. Even though they are, indeed, consuming around 100mA even when idle – it’s something for the start, later on we can grab something from TI to ensure power efficiency.
On this PB, I also plan putting BT and WiFi modules. I’ve seen WiFi modules for, like, 6-7EUR each, that had good Linux compatibility and could be soldered directly onto PCB with pads prepared for that.
Will have to find BT modules like that, though – BT is my concern as I feel I’ll be using it actively.
sample design pics here
Also, I’ll certainly have an IR sensor and IR LED on this PCB, along with some DS18B20’s and MB other stuff that I could develop on. See, as it is a wearable computer, some of temperature sensors are certainly going to be stuffed under the clothes to log the temperature of my body with 0,01 Celsius grade precision. Pulsoximeter will follow this shortly after that, and I definitely will add something more 😉 One more thought for this device – it could be the thing that registers when I fall asleep, just to turn off the lights and lock my PC so that nobody will blame me for leaving lights on and PC working =)
I could think of many usages, like a mobile phone/PDA replacement, audio player and stuff like that – the problem is I haven’t started actually working yet. I don’t even know if the RPi I’m holding in front of me right now is in a working condition – I occasionally threw it in my school bag and it got some minor injuries there, none of those look critical but there might be some critical ones that just can’t be seen easily. So – the whole project depends on whether mine RPi is working. I’ll provide updates when I have them =)
Gotta go and strip ALL the connectors off!
And no, it’s not an April Fools joke – updates are to be coming soon 😉