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.

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]

[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.