The many features and beautiful simplicity of the venerable Arduino, have captured the minds and imaginations millions of hobbyists, programmers, and Roboteers. 
Today, I'm going to discuss the Teensy 3.1. | Technical Specifications | ||||
| Feature | Arduino
Uno R3 |
Arduino Mega2560 | Teensy 3.1 | Units |
| Price | 25 | 54 | 19.8 | US Dollars |
| Processor | Atmega328 | ATMega2560 | MK20DX256VLH7 | |
| Bits | 8 | 8 | 32 | |
| Core | AVR | AVR | Cortex-M4 | |
| Rated Speed | 16 | 16 | 72 | MHz |
| Overclockable | 24 | 24 | 96 | MHz |
| Flash Memory | 32 | 256 | 256 | kbytes |
| Bandwidth | 16 | 16 | 192 | Mbytes/sec |
| Cache | 0 | 0 | 256 | Bytes |
| RAM | 2 | 8 | 64 | kbytes |
| EEPROM | 1 | 4 | 2 | kbytes |
| Direct Memory Access | N/A | N/A | 16 | Channels |
| Digital I/O | 14 | 54 | 34 | Pins |
| Voltage Output | 5 | 5 | 3.3V | Volts |
| Voltage Input | 5 | 5 | 5V Tolerant | Volts |
| Analog Input | 6 | 16 | 21 | Pins |
| Converters | 1 | 1 | 2 | |
| Resolution | 10 | 10 | 16 | Bits |
| Usable | 10 | 10 | 13 | Bits |
| Prog Gain Amp | 0 | 0 | 2 | |
| Touch Sensing | N/A | 64 | 12 | Pins |
| Comparators | 1 | 1 | 3 | |
| Analog Output | 0 | 0 | 1 | Pins |
| DAC Resolution | - | - | 12 | Bits |
| Timers | 3 | 6 Total | 12 Total | Pins |
| FTM Type | 0 | 0 | 3 | |
| PWM Outputs | 6 | 12 | 12 | |
| PDB Type | 0 | 0 | 1 | |
| CMT (infrared) Type | 0 | 0 | 1 | |
| LPTMR Type | 0 | 0 | 1 | |
| PIT (interval) Type | 1x8bit 2x16bit | 2x8bit 4x16bit |
4 | |
| Systick | 0 | 0 | 1 | |
| RTC (date/time) ** | 0 | 1 | 1 | |
| Communication | ||||
| USB | 1 | 1 | 1 | |
| Serial | 1 | 0 | 3 | |
| With FIFOs | 0 | 0 | 2 | |
| High Res Baud | 0 | 0 | 3 | |
| Fast Clock | 0 | 0 | 2 | |
| SPI | 1 | 1 | 1 | |
| With FIFOs | 0 | 0 | 1 | |
| I2C | 1 | 1 | 2 | |
| CAN Bus | 0 | 0 | 1 | |
| I2S Audio | 0 | 0 | 1 | |
| FIFO Size | 0 | 0 | 8 | |
And to appease the readers of Hack A Day .... 
A Stepper motor has multiple coils that when energised in a certain sequence, produces defined accurate "steps" of the shaft. The NEMA 17 Stepper Motor shown here, seems to be the DIY 3D printer industry's favorite. It provides 1.8° per step accuracy. As long as your software can initialize the linear travel with endstop switches, mechanical or optical, then it will know at all times where along the axis it was left. There is little issue with "drift". When you cut the power to a stepper motor, it stays exactly where you placed it. Yes, of course you can "push" the carriage without power but for the most part an energized step will place the shaft in a known spot. Speed is managed by the frequency in which you cycle the steps.
A DC motor, on the other hand is pretty much "free running". You apply a DC voltage to the winding, and the shaft will spin in one direction. Reverse the polarity and the shaft will spin in the other direction. Torque is based on electric current capabilities, and is a factor of the wire gauge and number of windings. Speed is related to the voltage applied. Most DC motors in a control context are driven via Pulse Width Modulation or PWM, but still have no feedback as to the position of the shaft, or in my case linear carriage. When you remove power from a DC motor, it will coast until it stops. To remedy this, you need to employ Dynamic Braking. Accuracy is non Existent.
Every 3D printer I've seen A repstrap is a 3D printer cobbled together from whatever parts you can find, which will eventually allow you to print the parts for a reprap machine, or to simply use as a stand alone machine. Derived from the term bootstrap, as in "to pull yourself up by your bootstraps"A RepStrap is a open-hardware rapid prototyping machine which is made by fabrication processes which aren't under the RepRap umbrella yet. These are becoming less and less common as RepRap printed parts become more available, but are still an option. You can build a 3D printer RepStrap using a tablesaw, orusing a lasercutter, and use this to make fun, beautiful, useful things.
According to WikiPedia: Optical linear encoders[1][2] dominate the high resolution market and may employ shuttering/Moiré, diffraction or holographic principles. Typical incremental scale periods vary from hundreds down to sub-micrometre and following interpolation can provide resolutions as fine as a nanometre.And...
OverviewFor those who enjoy scavenging, many components useful for constructing 3D printers can be found in inkjet printers. This often includes optical encoders and strips. This page gives information on finding and using these items.
Finding printers with linear optical encoders in themCheap inkjet printers can be obtained from garage sales or recycling centers. Do not get laser printers, since they do not have the right optical components in them. Not all inkjet printers have optical encoders and strips in them. It is easy to tell by opening the lid (as if to change the ink). You should see a grey plastic strip close to the shiny metal rod and running parallel to it. The printers that people sell cheaply or recycle generally are somewhat inky inside. Do not get ink on the optical strip, though you may be able to clean it off.
The strip runs through the optical sensor, which may be quite hidden. It is probably on the back side of the assembly that holds the ink cartridges.
