Surj

Morning all,

Okay so we want to make the phone. It'll have to be reasonably portable and at some point I can harangue one of my design friends like Paul Lupson into making a case for it. But in the meantime we still have to prove that the idea is valid and that indeed we can build a Linux cell phone.

I started looking for parts and the first thing that we need is a really small Linux computer. So Google yielded me some interesting results most notably this resource list of Linux Single Board Computers (SBC's). Also check it out for an excellent primer on small embedded computers.

http://www.linuxdevices.com/articles/AT8498487406.html

Okay, so like a good geek I pored over the details and visited the websites. I wanted maximum bang for the buck. What I got was just Maximum buck. I called a lot of them up and found out that the boards are perhaps 300 - 400 bucks with the eval kit at 3000 dollars. Sod that.

Luckily my pain was eased when a friend said "have you looked at Gumsticks?" after searching for a while it came to be clear that Gumstix is the correct spelling and the website can be found here

http://www.gumstix.com/

Great basic overview
http://linuxdevices.com/news/NS3967182515.html
(Rendezvous? precompiled - oooh sir, suits you sir)

The design is open and the site also sells these things ready made. I'll repeat. I am a bad hardware hacker and as such I want to keep fuss to a minimum. There was the time I was working on eye tracking boards at the media lab and staying up late staring at oscilloscope screens hoping for divine intervention. I code better. That’s why I want this device. Focus.

Quick tangent: - "why not get a phone like Motorola's A760 and save yourself the hassle?"

Answer - Had a bunch of them when I was at Orange. About as open as a vault where they have lost the key. Get this - non standard Linux flavours, "proprietary API's", teams within the company that won’t reveal API's to each other. Welcome to the bleeding edge of technology.

So we want one of these

http://www.gumstix.com/

Next and most important is how we connect to the GSM layer that is all around us.

Now this is the bit where I do know that farting around with buggy protocols and the like will upset a lot of people. So if we can get this module as a working chunk of circuitry the better.

Now I had worked on a Machine to Machine (M2M) startup called Machinecast and had some knowledge of a great little device called a GM 862 unit. We had basically used them as a GPRS modem so we could give cell phones to washing machines and cars and get all wired magazine with the world around us. We built the units and made some great software thanks to genius's like Louis Lopez (MIT EECS) and Deva Seetharam(MediaLab).

So here is this discrete data module called a GM 862 but little known fact about it. It has all the basic circuitry for Voice included as well. Go check it out. Basically add a sim, add some power and control the device via a serial port. Lush.

http://www.gm862.com/gm862/gm862PCS.htm

also some great support forums here as well - nice, always useful

http://www.roundsolutions.com/forum/

Better still - look , a US supplier and some real guides to using it (friend Nathan Seidle - they used to run this from a dorm room and are booming - congrats)

http://www.sparkfun.com/shop/index.php?shop=1&cart=360219&cat=75&

Explore the site and this article is fun to read gives great tips on getting the voice working.

http://www.sparkfun.com/tutorial/Port-O-Rotary/portable-rotary.htm

Okay. Key design decision here.

We can get a small linux SBC and control the radio stack via a serial port. Sweet.

No terrifying electronics and line level matching and what not. Lets keep it simple stupid.

This also means that I can prove the concept with a standard Linux machine as well. Since at the serial port we have a divider between the "blocks" I could get my trusty P3 Debian box and test with that. That’s what I'll do for the next post.

Let’s finish this post.

We need a screen. We could have a touch screen and then that way have the UI based around that - okay sounds plausible.

Let’s hunt at Earth LCD. This is a likely candidate

http://store.earthlcd.com/s.nl/sc.7/category.297/it.A/id.4233/.f

But it only works on USB. USB Host is unlikely on a SBC. Okay another option would be just the screen. Here is an article on connecting that together with the Gumstix.

http://www.gumstix.org/tikiwiki/tiki-index.php?page=Display

Wow. You skin your phone like winamp theoretically.

Okay. Parts on order and since I have a GM-862 module, I will do the first test and get it working with the Debian Box. This will allow me to get the module and the mic/speaker bit working and tested and then migrate that to working with the Gumstix.

Okay got to go. I'll post those block diagrams I promised in the next post with results from my block level test.

Stay tuned for further reports.