PropScope - 2 Channel Oscilloscope


Price (USD)
$199.99 ea.

The PropScope is a two-channel oscilloscope that is capable of reading 25 million samples per second with ten bits of resolution over one, two, ten, or twenty volt peak-to-peak waveforms.

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USB oscilloscopes used to be a bit of a novelty. Sort of useful; more of a joke. They didn't have a useful frequency range, or the software was written, well, by engineers (not user-interface experts). Fortunately, Parallax has been keeping up development of their own USB-based oscilloscopes, and have leveraged their skill with the particularly powerful Propeller microcontroller into this latest version.

From the technical documentation, the PropScope offers the following features:

  • 2 input channels
  • 25 Msps Maximum Sample Rate (that's 25 million samples per second)
  • 20 Vpp maximum input range (-10 V to +10 V when DC-coupled)
  • 10-bit input resolution over either the entire 20 Vpp range, or selectable 10, 2, and 1 Vpp ranges.
  • 1x/10x selectable probes
  • Power requirements: USB powered
  • Communication: USB
  • Dimensions: 2.71 x 4.67 x 1.08 in (68.8 x 118.6 x 27.4 mm)
  • Operating temp range: +32 to +158 °F (0 to +70 °C)

The PropScope makes it's measurements with 10 bits of resolution over 1, 2, 10, or 20 volt peak-to-peak waveforms. What does that mean? Let's start with the term "10-bits of resolution". That's a number meaning 2^10, which is actually 1024. The PropScope will split the voltage range you by 1024 steps to make it's measurement. For example, if you are measuring a signal that changes more than 2 volts, it will give you accuracy of (2V / 1024) = 0.0001953125 volts per step. At the other end of the range, if you are measuring a 20 volt signal, you will have measurements in steps of (20V / 1024) = 0.01953125.

So you are going from a measuring accuracy of 0.195 millivolts when on the 2V range to an accuracy of 19.5mV. That means your measurements will go up and down in ~0.2mV jumps versus 20mV jumps. And of course, you want as much accuracy as possible, so always select a voltage range as close to the maximum voltage as you are expecting to measure!

Here's another way of thinking of it. You are trying to measure & confirm a voltage you happen to know is 1.928 volts. If you select the 2V range to measure it with, the PropScope will return a value of 1.9277V. Pretty close, right? That's the closest number of the 1024 steps available between the range of 0 and 2V. But at 20V, the closest number is 1.9219V

The PropScope can sample at 25 million samples. Ok, so what does that mean to you? General consensus is that you need approximately 10X the frequency of what you are measuring to get a reasonably accurate idea of what the signal is doing. For the PropScope, this means 25 million samples per second / 10 = 2.5 million cycles per second it can watch with reasonable accuracy. Of course, you can trade off accuracy for more speed if that's what you need. At a 10x oversampling, you get 2.5 MHz (megahertz), which is quite usable. BUT, since you have two channels, you have to split than again in 2, meaning a maximum of 1.25MHz per channel. Not bad, not bad at all!

Beyond the capabilities as an oscilloscope, the PropScope has other very useful features that round it out as a solid workbench companion:

  • Function Generator
  • Logic Analyzer (watch a bunch of microcontroller pins all at the same time)
  • Spectrum Analyzer (see what frequencies make up that noise)
  • Vector Scope (
  • ...and more, apparently. There's a lot to explore with this tool!

There's even an expansion card, which offers these additional features:

  • External analog trigger with a -10 V to +10 V input range
  • 4-bit digital input and trigger
  • Arbitrary waveform generator with an 8-bit DAC and selectable -1.5 to 1.5 and 0 to 4.9 voltage ranges
  • 4-bit DAC for generating NTSC and PAL signals

The included software provides a traditional scope interface along with auto measurements and the ability to store and export waveforms.

Parallax is a company with a bunch of smart people, and some excellent technology. Expect the PropScope to develop into a very useful tool!





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