Homebrew PCBs

On Sat, 26 Aug 2006 19:15:28 +0200, purdueee_06  
<nathanael.huffman@...> wrote:

> I've been looking at Volkan's tutorial and I'd like some clarification
> on a few points:
> 1- why does the paper needed to be emulated... won't the PCB tray act
> like paper?

If you look at my mod, i've done just that. The tray has a cutout on the  
side so you can put it in the printer before printing and the traction  
roller already grabs it. I simply moved the optical sensor so it senses  
the "delayed" leading edge directly, where the cutout is.

> 2- which sensors will need to be emulated?

Depends on printer. With mine it was only the paper detection sensor on  
the back. In the service util there is talk about a paper sensor on the  
head, but i couldn't confirm that so far nor did it give me grief.

> 3- Are there any more specifics on what needs to be monitored?
> 4- how is the moved optical sensor used.

Dunno what you mean with the last two.

> Any other clarification would be helpful as well.
> I have the repair manual for this printer, but I'd like a little bit
> more on the theory behind the electronics modifications.  If I can get
> a bit more information, I'd be interested in releasing a step-by-step
> how-to on the printer, complete w/ my own source code and
> schematics/pcb layout to help others create functioning PCB printers.

I dunno why volkan needed the electronics for the 4200, i do not know that  
printer. All i can say is with the c84 it worked nicely the way i did it.  
The trick is to get the cutout the right length so the time delay between  
the motor starting to pull and the edge triggering the sensor is right. I  
worked that length out by fixing the sensor and making a very far back  
cutout at first (actually i just used tape protruding over the edge  
instead of a cutout). Now you can manually pre-feed the carrier into the  
printer variable distances and find for which starting positions the  
printer will detect a successful feed. When you know the valid distance  
you can make the final cutout just the right length so you only need to  
feed a few mm.

BTW i found the optical sensor is less precise than the timing/number of  
steps of the paper feed. So to get accurate repeatability i made a stop to  
push the carrier against. If you always put the tray in the same starting  
position there is zero error.

ST