SparkFun Forums

[localghost]

Hello,

I am pretty new to the field of circuit design but I am keen to
learn. I would like to build a circuit for a project I am working
on. The design is extemely simple as far as I can see, however, it
uses a surface mount chip. Basically I want to convert TTL video
signals to LVDS. i.e. connector from graphics output -> converter IC -> hirose connctor to LCD panel.

I am thinking of using a chip similar to http://www.national.com/ds/DS/DS90C363.pdf

Basically I am not so sure I know exactly what is involved and can't
seem to find the information to help me. For example, I assume I
can't just create a design which simply wires up the connectors to the
IC? Some resistors are neccesary? Although I don't fully understand why they are neccseary and therefore how to calculate their values.

I want to create the design in the Eagle Layour Editor and get the PCB
made by batchpcb (I assume DIY methods would be hopeless at create
0.5mm pitch designs?).

If anybody could shed any light on how to proceed with this project I
would be most grateful.

Many Thanks

[winston]

The best thing to do is to see if the manufacturer has an application note with the reference application circuit - many do. Also you may want to look to see if there's a layout guide for the chip to help you decide how to lay out the PCB. (If normal good practise should be followed for this particular chip, there may not be a layout guide at all specific to the chip. Google "PCB layout" and spend the next three days reading contradictory advice )

I have no experience with this particular chip, but a quick skeet at the datasheet suggests that you would just connect its TTL compatible inputs straight to the circuit that's generating the video (presuming your circuit is already generating the TTL video data in the right format). The passives that are absolutely necessary will likely just be decoupling cacpacitors for the power supply pins.

You'll find DIY PCB methods can actually get surprisingly fine pitch. DIY methods for PCB making can get finer than 0.5mm pitch, in fact, 0.5mm pitch is only slightly less than the "10/10" (10 mil tracks, 10 mil spacing, i.e. 0.254mm tracks, 0.254mm spacing), which is considered easy. 0.5mm pitch is only 4um (yes, micrometers) less than "10/10" rules. I've done double sided boards at home with 0.4mm (0.2mm traces, 0.2mm spacing) pitch using the toner transfer method (i.e. my tools to get the etch resist on the copper clad board were a reasonable laser printer, cheap "inkjet photo" paper, and a clothes iron). Some people say they've got down to even finer than this with the toner transfer method, but by then it is starting to get a bit tricky!

[localghost]

Hi winston, thanks for the reply

I've just been reading your posts about home PCB printing - very interesting indeed! You mentioned you got the paper from Tesco - does that mean you're in the UK? If so can I ask where you get your components from - I have been looking at getting parts from Farnell?

Regarding the actual chip - this project is just for my own interest really so I can use any LVDS encoder chip. I far as I understand now I can just wire up the "data" lines straight through but the power lines require some extra components. These will be capacitors - I assume this is simply to protect the circuit from spikes and provide a smooth flow? If I am getting this right - how do you go about calculating the value of the capacitor to use in this or any situation?

The "data" output from the video circuit seems to be compatible with the chip and the power supply line is at 3V / 60mA. The input to the chip has many different values but from what I can make out it will accept 2.7V -> 3.3V so the provided 3V line should be OK? any need for a cap here? But the input current is 5.1uA. Massive difference here so I guess it needs a resistor to drop the current? Again I am unsure how to calcualte this (V=IR?)

So...If that it about right I just need to add resistors and caps inbetween the different power levels but "data" can generally connect straight up? Or am I completely missing the point?

Sorry about the thousand questions
Hopefully, if I can get my head around this, I can start making it much sooner than I thought if I don't need to get the board printed in the US

[leon_heller]

If I were you I'd start with something much simpler, this project seems way over your head.

Leon

[bigglez]

Basically I want to convert TTL video
signals to LVDS. i.e. connector from graphics output -> converter IC -> hirose connctor to LCD panel.

Greetings (No Name Supplied),

Are you sure that the "TTL Video" is the correct signal
for the LCD panel, and that only level shifting to LVDS
is required?

AFAIK, LCD panels use serial data with LVDS format
physical connections to reduce the number of interconnects
(through the hinge of a laptop, for example).

The LCD requires multiple data for each PIXEL, a
grayscale if BW and RGB data if colour.

Do you know the names of the signal pins on both
the video source and the LCD panel?

Comments Welcome!