Oscilloscope Throwdown -- Episode 311

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Ben is happy because he’s standing in front of a table full of oscilloscopes. Felix wants to know what oscilloscopes are and why they’re here.  In this episode Ben and Felix evaluate oscilloscopes from Tektronix, Rohde & Schwartz, and Keysight.  They discuss the differences between the scopes, what they can do, and put them through the paces.

The first scope they look at is the Keysight DSOX 1102GKeysight DSOX 1102G. It’s a smaller scope, it’s slower, it’s only 70 mHz,  but it’s basically Keysight’s introduction to the entry level range of affordable scopes.  As such, it only has 2 channels. Scopes should have at minimum 2 channels because observing the differences between 2 signals is quite important.  They discuss some of the basic features of the scope, how it differs from the other scopes, and then they’ll use it to reverse-engineer the data signals going to the LCD screen of a portable DVD player.  They are trying to find the TTL pins on the LCD screen because they want to hook it up to a Raspberry Pi.  They come across some strange signals on the LCD that they weren’t expecting so decide to run the same tests with the next scope which is at a higher speed grade.

The next scope that Ben and Felix look at is the Rohde & Schwarz RTB2004Rohde & Schwarz RTB2004. It features four channels, universal knobs, a touch screen, and is about 4x faster than the last scope.  Of all the scopes the team looked at, the Rohde & Schwartz RTB2004 boots the fastest.  Felix points out that the firmware on it is rtos, a real-time operating system that’s open source.  As the scope has more memory, it allows you to capture a “wider” event, such as the entire frame of a video signal. The scope has triggers on video where it finds, not just a low pulse because the video is an analog signal, but it looks for the specific stair-stepping that indicates that it’s the edge of an NTSC line and it can sync to it.  A trigger is a when you set your scope to look for a certain type of signal.  When a scope is triggered it can pause (‘run single’ setting) or align the display to the start of the event.

The Keysight MSOX3054TKeysight MSOX3054T is the next oscilloscope the team looks at At 5 gigs per second and 500 mHz it’s a little faster than the Rohde & Schwarz scope they just got done looking at. An FPGA powered demo board is included with the scope and gives the team a range of signals to learn their new scope with One of the signals is SPI which stands for serial peripheral interface and is used with such things as SD cards sensors flash memory and more The four channels used by the scope come in handy since SPI uses a minimum of 3 lines More advanced scopes such as this one can trigger on data patterns within signals Ben locks in the threshold level which is the triggered voltage level and they take a look at the bus analysis Ben and Felix like the interface between the touch screen and physical buttons Another thing they like is having controls for each channel

Finally, Ben and Felix take a look at the Tektronix MSO58Tektronix MSO58. This is a very high-end scope with 8 channels and a small computer inside. They are going to take a look at to see what it can do that the other scopes cannot.  Ben hooks up an old Atari 2600 with the game Frogger to the scope.  They also have it hooked up to a secondary LCD screen to make sure that it works.  They look at the crystal oscillator frequency going into the video chip and see what its timing is.  They then try to replicate it using the arbitrary function generator. They get a frequency measurement of the NTSC color burst. They look at the output chip and show you what the signals for the pixel clock and CPU clock look like. Felix sets up the AFG setting on the scope while Ben breaks the traces on the Atari that will allow them to jumper the signal in. Ben cuts the trace from the oscillator to the graphics chip in order to replicate the signal using the arbitrary function generator.

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