Archive for September 2009

Schematics and 3D

September 23, 2009

Okey so i have did some real design work and drawn up  a schematic for that shield and actually even decided to try out the 3D feature of my PCB design software.

The schematic is far from final yet tho, this is just the beta of it. I will check a few things with it to make sure it works like it supposed to as fixing it later can be very difficult

xmos schem tunimb

xmos 3d board


Information gathering

September 18, 2009

So the beginning of designing anything is gathering some technical information on what you need to make it work. The main thing is to figure out what ICs to get for the job.Here a lot of things need to be considered from voltages they work on to communication protocols they use to make sure everything can talk to each other.

Luckily the ethernet is already taken care of on the board, so we dont have to worry about that.Next big thing is the IDE hard drive. As you know the IDE interface has a whole pile of pins, but luckily a lot are unused (gnd,obsolete,safety…). The most important group of pins are the 16 data lines that form the 16bit parallel bus along those are the flow control lines for it (read,write and such) and also a few address lines.Then there are a few extra pins like a reset,busy,interrupt etc. All this together gets to about 24 I/O pins and the board happens to have 24 I/O per core on the headers so its exactly enough pins to interface it. Okey so we have enough I/O but also the levels must work. Our I/O is 3.3V and 5V tolerant, but the IDE bus happens to use the 5V levels. Okey that sounds like a gazillion level shifters but the IDE bus works by the TTL standard so it should see a 1 when the voltage is above 2V so that means our 3.3V can generate a high level on the bus.I will still look in to that but from what i seen now there should be no problem just sticking the IDE bus directly on the I/O pins. Also the IDE Hdd needs a 12V supply along its 5V supply so a 12V power source will be used that will regulate down to 5V

While we are at mass storage lets look at the SD card now then.The card is much friendlyer to interface as it first of all only needs a low power 3.3V supply to work. Then the next beauty of the SD card is that its interfaced over the good’ol simple SPI bus on 3.3V levels, also by the SD spec it works up to 25Mhz so thats quite a impressive data rate.

Also on the topic of memory is the FRAM chip.It is a new memory technology called magnetic RAM that is quite revolutionary. It is the speed of RAM but it keeps its memory like flash, also there is unlimited write cycles.I happen to have one of these 1Mbit chips so im going to use it as memory to store various big stuff. Also one nice bonus is that the SPI bus on it works at up to 40Mhz and its a 3.3V chip so it will work with my I/O.

Moving on there is the matter of getting analog audio in and out.For that i plan to use audio DACs and ADCs that work with the standard I2S bus.That means the communication cosists of 3 clocks (master,bit,L/R) and 1 data line.The I/O should be esaly capable of making this interface run.Also a nice thing is that the digital I/O on these is usually 3.3V.

One interesting thing is the bluetooth module. Its a very cool chip from National Semi that contains a 8051 MCU (bluetooth stack) along with a 2,4Ghz radio and a antenna all inside the chip! By default the module is a virtual com port on bluetooth and the standard USART signals on the pins. It can also be told over the USART interface to do other stuff like connect to others or act as a bluetooth headset and such. Really cool chip that only needs a RX and TX line to work. Also confidentiality its all 3.3V too.

Only thing left is the LCD that I’m not sure if to really put in to it yet.However this is where the 3.3V ends as the display needs 5V to work however on the displays i have the I/O dose take 3.3V as a logical high so it is possible to interface without level shifters.

So thats about it in the end there are no 5V level shifters needed (I was scared i will need a truck load) and the IC count is pretty low in the end(around 4)  Only thing is that i don’t know if i will be able to fit it all on to a credit card sized PCB as i make my PCBs at home but i will see that when i get to PCB design.Main worry are the connectors as there is little room for them (especially the huge IDE connector)

Got a block diagram

September 16, 2009

So i have put down some design ideas what to put in to the design and what core to assign it to. As you can see there are quite a few components here.

Block diagramNow the only thing that is already on the XC-2 board is the ethernet part (luckily), but all the other stuff will have to be added to make the thing work like its supposed to. The next key component is the mass storage that is going to be a IDE harddrive or/and a SD memory card. The SD card should actually be on core 3 as it handles the file system but i ran out of pins since the IDE drive needs a whoping 24 pins to interface, but since the SD card uses standard SPI i figured i would connect it then to the same SPI bus that goes to the external memory.This memory will be the new FRAM type (nonvolatile magnetic RAM) because it is very fast and will be used to store various stuff like the website it is going to host and things like that. The next thing is the audio that i will use standard audio DACs and ADCs on a I2S bus and will be connected to its own core that will hopeful decode a few audio formats. Moving on we get to a bluetooth module, that is a simple BT module from National Semi with a USART interface and is intended for a interface to mobile phones directly. The last is a simple character LCD to display some info on its current state. The LCD is not very crucial and may be scraped later as the device was not ment to be interfaced directly but rather trough ethernet/bluetooth. Another thing is that the change in supply voltage is needed because IDE drives need along the 5V also a 12V supply with some current on it too as it runs the mechanics.

For now I’m still only waiting for the development board.

What’s the project about?

September 3, 2009

So the big question is what is the project actually about. It is a sort of media center/server . Its job is to mainly play back audio  (video is probably way too difficult) and host it inside the LAN for other devices, or also stream it over the web to a mobile device you your music is everywhere you are.

The project is still sketchy.Its more of a idea currently that i will develop further.The storage for it should be a hard drive or similar as they provide the highest capacity storage, although may use a simpler SD card for test purposes. I will try to get the MP3 decode/encode to happened inside the XMOS chip if possible(external decoder chip as alternative) As for the user interface i am thinking of a webserver like routers and other home network equipment uses as its very user friendly and easy to use. But i also am thinking of using a small LCD module to display some status and stuff on it.But a lot more features may come in or a lot may get scraped. It has to be determined how complicated certain features are to implement also lots of new ideas always spring up during the development of a project.

I hope the project will become what i imagined it to be, in any way it will be a good learning experience as there are a lot of different technologys involved with it.One of the biggest is the new XMOS chip it self.

The begining

September 1, 2009

This is my brand new blog where i will start posting development on my new project that is part of the new design challenge from XMOS.