Projector calibration on uneven surfaces made easy

projector-calibrator

If you are thinking of building your own flight/racing sim setup at home, you might want to check this out. [Alex] from the Garoa Hackerspace in Säo Paulo, Brazil put together a slick setup that makes projector image calibration a breeze.

When building a wraparound screen for such a simulator, you are likely to run into problems with both overlapping images and distortion from the curved projection. There are projectors that can easily adjust themselves to work in this sort of setup, but they are often very expensive, so [Alex] thought he would build a solution himself.

After studying a paper written by [Johnny Chung Lee] in 2004, he built a prototype display calibrator last year that used similar, though slightly tweaked methods to get the job done. This time around, [Alex] has improved his calibrator, making the process more precise and a bit quicker.

Light sensors and an Arduino are attached to the back of the projection medium, and a large broad scan of the screen is performed by the projector. His code then triggers an additional sweep of each corner to better estimate the exact edges of his projection surface. Since the video is tweaked in software rather than relying on the projector hardware to handle the task, the result is cheap and very accurate.

Don’t take our word for it though, check out [Alex’s] video demonstration below to see his calibrator in action.

[Read more...]

Is your camera lying?

It is easy to rely on the ratings marked on different tools, whether it is a power supply, scale, or speedometer. However calibration is essential for any part that is relied upon either professionally or for a hobby. [Jeremy] wanted to see if his Lomography camera shutter really was only open for 1/100ths of a second when set to that. In order to test his rig, he set up an LED on one side of the shutter, and a high speed phototransistor to gauge the time spent open, using an oscilloscope to measure the time the reference point was pulled low. In his case, when the camera was set to 1/100, the shutter was actually open for closer to 1/150th of a second (the mean was 1/148ths of a second, with a standard deviation of 417 uSecs). This difference can make a large difference in picture brightness.

Be sure to check his blog for more pictures of the setup, as well as some useful part references and circuit diagrams.

Calibrate those instruments

This tip was a pleasant surprise on a Sunday morning. This site explains cheap and relatively easy ways of calibrating the instruments we hold so dear. Not only how, but when and why. Included are instructions on calibrating Voltage (DC and AC), frequency, RF and more.

[thanks Jan]

Capacitance sensor guide (AD7746)

capacitive_sensor

[Marcus] has written up his experiences using the AD7746 capacitance sensor. He used the SparkFun breakout board in conjunction with an Arduino. The available Arduino code wasn’t that great so he rewrote it to be easier to understand. The AD7746 is an I2C device that can be continuously read, but this doesn’t mesh well with the Wiring libraries. Additionally, the calibration routine from the data sheet is difficult to understand. He’s included all of the code he used plus a Processing sketch to help visualize the input which will hopefully make your experience with the chip much more smooth.