Arduino Eye Shield

Posted on Feb 6, 2014

The Arduino Eye Shield is a circuit board that can be plugged on top of the Arduino allowing it to interpret analogue video ( PAL or NTSC ) from a camera or other source. It gives the Arduino the power of sight. There are many applications for this. In the example below the video information from the camera is used to drive an 8x8 LED matrix (with

Arduino Eye Shield
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a MAX7219 and the Arduino Matrix library ). The PAL and NTSC formats have a relatively straightforward structure. For each line we see a negative-going pulse, then a colour burst, followed by the picture information - where the brightness is determined by the voltage of the signal. Lines follow sequentially to make up a full picture, with additional synchronisation pulses to indicate a new frame. In the example below we see two lines (and the pulse and sync of the next), where there will be two darker vertical features against a brighter background. For a more complete description see: PAL video timing specification. In the circuit below the LM1881 (IC1) separates the synchronisation pulses from the video signal, allowing the Arduino to identify a specify line of the picture. To read the information we need to sample the changing voltage along the line, which for PAL takes 52uS. The Arduino`s AnalogRead is too slow (taking about 100uS per sample). The solution used here is to digitise the video signal using a simple comparator circuit, which can then be read by a DigitalRead operation that takes about 4uS, allowing for operations to store the read value, this allows at least 8 samples to be made per line for the picture. The comparator ( AD811, IC3) sets its output either high or depending on whether the video signal is above or below the reference level. The reference-level is set dynamically by the Arduino. To obtain...

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