Fun With an Inexpensive Oscilloscope

Introduction

Oscilloscopes used to be quite expensive pieces of kit, usually beyond the means of casual hobbyists. Nowadays there is quite a selection of inexpensive oscilloscopes on the market and I purchased a FNIRSI 1014D on Prime day for $200 CAD. This is a dual channel 100MHz Oscilloscope which also has a built-in signal generator. At that price, you can’t lose. If you want to measure computer speeds in the GHz range, then you need a much more expensive device; but, for plotting frequencies under 100MHz and generating signals of a few MHz it is ideal.

The screen is quite nice and readable. The controls are simple enough and there are some good youtube videos on how to use the scope. The documentation is quite terse, so watch the videos.

Useful for Ham Radio

One of the members of the Sunshine Coast Amateur Radio Club had a couple of HF radios that weren’t working correctly. To diagnose the problems, both the oscilloscope and signal generator functions were quite helpful. In the picture below we are generating a triangle wave and feeding it into the antenna of one of the radios. We can then see if it is decoded into sound or trace how far it gets through the radio. In this case the radio worked fine on receive, but would fail to transmit. The problem turned out to be a bad power cable which provided enough power to receive, but not transmit.

I recently built a QRP radio from a kit where the instructions included diagnostics that could be obtained via an oscilloscope as well as points to inject a signal to test the  various parts. The radio worked fine after I built it, so this wasn’t entirely necessary, but below is a picture of the signal from the speaker output that you plug into your computer’s microphone jack to receive the radio’s signals.

Work with Microcontrollers and FPGAs

Although computers tend to operate at frequencies faster than this oscilloscope and a logic analyser might be a more appropriate tool, it still has its uses. For my upcoming book on RISC-V Assembly Language Programming, it includes examples interfacing to external devices and doing operations like flashing LEDs. Originally, my program didn’t work, but with the oscilloscope I could see the outputs of the microcontroller were correct, so then I knew the problem was in the circuit I built.

Most external communications protocols work at speeds the oscilloscope can handle. Further most microcontrollers can be slowed down, so you can operate at a speed the oscilloscope handles for testing purposes.

Along similar lines, I like playing with FPGAs and I recently received a Tang Primer 25K which doesn’t come with a lot of bundled devices, so creating a Verilog program for it, one way to see what it is doing is via the oscilloscope.

Downsides

A common criticism of this oscilloscope is that it doesn’t reliably work at 100MHz, that practically speaking you need a slower frequency to get a reliable plot. For the signal generator it works fine at the bottom of the HF range of frequencies but higher frequencies would be nice. On the other hand improving in these areas would raise the price and I’ve been able to work within its ranges and be productive. Also keep in mind that its specs look good when compared to older much more expensive scopes.

The documentation is quite terse and not that helpful, however there are a number of good videos on how to use it.

Summary

For the price, this is a great oscilloscope. Especially if you are working in the HF frequency range of ham radio. I find the scope quite helpful with my electronics projects involving microcontrollers and FPGAs.