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Monday, May 23, 2011

PCB design with gEDA notes

I've been using gEDA on ubuntu linux for schematics and PCB design and like it so far.
It had several key attributes.  Free and no limits on complexity or commercial use.

Found this site that may have some nice templates, making note
http://www.electronics-lab.com/blog/?p=6925
http://lowvoltagelabs.com/2010/11/16/arduino-shield-board-outline-in-geda-format/
Loaded it and it looks good, saved a lot of time finding the locations and sizes of
the connectors.

Sunday, May 22, 2011

Notes on the heavy duty motor shield for Arduino


This is a heavy duty motor shield for Arduino

It uses the basic motor shield from adafruit.com, same software, but instead of an hbridge
driver, it uses 25A 60V mosfets for drive.  Purpose is to drive
drill motors from the Arduino.

Here is the circuit of a half bridge.  The extra devices on the left are
to convert the input & enable structure to a N and P drive.  It is important
to have a HiZ mode when disabled, where N=0 and P=1 and both
MOSFETs are off.  I hope to simplify this circuit but i don't want to make
major modifications to the adafruit.com library.  This is the lash up prototype:



Here is  a photo of the Arduino, a canabalized up motor shield on top (this was one i modified for stacking and later blew out an Hbridge IC on, doh!) for control, a breadboard full of the NPN and PNP needed to convert the interface, a prototype high current MOSFET driver board and a drill motor.  The motor power supply is not connected in this photo.

Lets see if I can post the little video of the motor test program.  It revs the motor speed up, then reverses, then stops and repeats.  Watch the little black gear and make sure your sound is on to hear the fun.


video

Now to clean up the board to the form factor of a shield, it will be somewhat dense.


Saturday, May 14, 2011

Idea for laptop LCD repurposed as a photoblocking license plate cover

OK, here is an idea so horrible I had to share it, since I've been on the photoblocking topic lately.

Another possible anti-speed camera technology is to repurpose an old laptop as an LCD chopper.   The idea is that the backlight and cover of the laptop screen will be removed so that the screen becomes a see through license plate cover.   The laptop will be programmed to display a series of black stripes across the screen that will move so fast as to appear like a gray tinted screen.  To a camera that freezes the motion, some section of the plate will always be covered with a black stripe and be unreadable.

There are all kinds of issues.  In my state license plate covers are illegal, maybe elsewhere they are not.   I do see people with them all the time, so I guess the police haven't pulled over everyone.  The LCD screen would not be the right shape for the plate, although maybe one could be found that is acceptable.   The screen might be pretty dark and earn you a ticket anyway.   The LCD will be fragile and certainly would not hold up to northeast US weather.   But since when has sanity stopped an inventor?

I wouldn't be able to do field trials where I live, but just making note of the idea while I wait for more LEDs to come.  I'll develop this idea more later.