avr oscilloscope nokia lcd

Posted on Feb 5, 2014

This is an easy to build X-Y oscilloscope. To try this an ATmega324P and two KAD0820 (same as National Semiconductor`s ADC0820 ) were used. Originally this oscilloscope was built around an AT90S4414 hence the external AD converters. Some rose and Lissajous curves were used to test this oscilloscope. This circuit looks a bit messy as built on the

avr oscilloscope nokia lcd
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protoboard, and takes a bit of experimentation to get it to work correctly. To begin with, I fed the same sinewave to both channels and once I got a reasonably clear diagonal line I proceeded to test other curves. The contrast setting for the LCD was set for a relatively cool 20 C (68 F) so if you try it in a warmer environment, your LCD could look a bit too dark. There are two analog to digital converters (ADC) one of which converts a signal for the X axis and the other for the Y axis. The data from the converters is scaled down and then used as coordinates to draw a dot on the screen. If you feed a sinewave to each channel with an offset of /2 radians, a circle will be drawn. The ADC0820 converters are in the WR-RD mode which is the fastest of both available modes, taking only 1, 5 uS to convert a sample, and the microcontroller reads them as often as it can from an infinite loop. The ADCs are read at a rate of about 1666 times per second, but the much higher speed of the converters is not exactly useless. I actually tried with the ATmega324P internal converters and with its slower conversion time, about 13uS, the distortion in the curves was too obvious. Both of the ADC0820s conversion cycles are started within nanoseconds so the conversions are almost simultaneous and it`s not necessary to correct for phase changes between both source signals. So instead of complicating the firmware to be able to use the Atmega324P...

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