Hardware LX Mod

[samtheeagle]

This is a little project I've been tinkering with for absolutely ages now... I keep coming back to it and making a little more progress. Some details of my previous work can be found in the following thread, just to give you an idea of what I'm trying to achieve:

http://stargazerslounge.com/showpost.php?p=1722829&postcount=11

http://stargazerslounge.com/showpost.php?p=1804753&postcount=30

I have carried out a bog standard LX mod as per these instructions: http://home.zonnet.nl/m.m.j.meijer/D_I_Y/spc900nc.htm Where I take a different approach is the generation of the LX control signal. This is traditionally a control sent from the computer via a com port. I thought it might be interesting to make this signal hardware generated and controlled by a potentiometer.

It was pointed out to me that without the computer sending the control signal it wouldn't know when to expect an LX frame back, but I've sorted that via a custom app which monitors the incoming frames. It keeps a rolling average score of 5 frames, and if it detects a frame that is brighter than that average it marks it as a candidate LX frame. I say candidate as it seems that up to 3 bright frames may be returned when the LX signal ends, so from these candidates I pick the brightest to be the true LX frame.

The issue I'm currently having I think is hardware related. The Arduino code that I run to control the LX signal is very simple. If the pot is below a certain value the LX mod is turned off. If it is above the threshold then an LX signal is generated, with the signal length a function of the pot value.

To get LX frames correctly returned I am finding that I need to insert a delay into the signal generator code after ending the LX signal and before starting the next. I've experimented with many many values, and around 200ms seems to work fairly well. But that feels like a seriously long time for the CCD data to be read out! I'm not an electronics bod at all, I'm just messing about here, but I was wondering if it's something like the LX control signal isn't dropping off immediately as the Arduino output pin is changed? Do I need some kind of "pull up/down" on the signal line perhaps?

It's 99% working now, but it defo still has a few quirks to it which I'd like to try and figure out... Any LX / electronics / Arduino experts out there with some ideas?

Thanks.

[samtheeagle]

Just found this Arduino tutorial: http://www.arduino.cc/en/Tutorial/Switch

It has a check to debounce the circuit when changing the pin state between low and high. They even use a value of 200ms, which sounds awfully familiar to me... Is there a way to speed up the debouncing?