How to design a transistor circuit that controls low-power devices (tutorial)

I describe how to design a simple transistor circuit that will allow microcontrollers or other small signal sources to control low-power actuators such as solenoid valves, motors, etc.

DIY Scanning Electron Microscope - Image Quality Improvements 2

I've made some improvements to the microscope that have increased image quality somewhat. Here is a quick list of the changes:

-Made a new acrylic light guide that allows the scintillator to face the sample directly. The pipe is curved so that the light is directed upwards into the photomultiplier tube. The size of my bell jar necessitated that the PMT be mounted vertically, which is not good since a straight light pipe would cause the scintillator to be aimed directly at the bottom of the chamber.

-Added coaxial cabling and a fully-shielded box to the PMT amplifier circuitry.

-Adjusted PMT load resistor, and eventually installed a potentiometer so that I can change the load resistance to best match the raster scan rate

-Changed PMT amplifier circuitry so that the images are not inverted with respect to normal secondary electron micrographs



This is a MEMs gyroscope. I pried off the cover to expose the die.


This micrograph shows some structure on the die. Hopefully with better magnification and resolution, I'll be able to see the MEMs gyro itself.




It appears to me that the blurriness in these images is somewhat constant across all magnifications. This leads me to believe that focus is not the main issue, and that the problem is with PMT signal recovery. Scanning at a slower rate should help this, but the PMT amplifier is AC-coupled, so the scan rate cannot get too low, and I also cannot see the image on the oscilloscope at low scan rates -- making focus and various other adjustments difficult. I also haven't found a good way to synchronize my camera shutter to the raster scan.

Piezoelectric Braille system with PC parallel port control and HV transistors

Here's a project that makes use of these electronic Braille characters: http://www.metec-ag.de/braille%20cell%20p16.html

I built a bunch of transistor amplifiers and use two 74hc373 chips driven by the parallel port to control the state of both Braille characters.

Excellent resource for PC parallel port control:
http://www.beyondlogic.org/spp/parallel.htm

Fiberoptic mouse with quadrature encoders and custom shutter buttons

Here's another project similar the the fiberoptic joystick that I built. It uses the same 62.5 micron telecom fiber to sense X/Y velocity as well as two buttons in a standard computer mouse. This mouse is designed to be used in environments were electrical signals cannot be tolerated.

My Tektronix contest entry

Vote for me here: http://mytektronixscope.com/videos/

I am using my Tektronix 2246 analog oscilloscope to show the image generated by my DIY electron microscope. The 2246 is operating in X-Y mode, with the channels connected to a raster scan generator. The vertical scanning frequency is about 30Hz and the horizontal frequency is about 10KHz. The trace brightness (Z axis) is modulated with the secondary electron signal from the microscope.