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Exploring the Scoppy Scope Oscilloscope Firmware

In this three-part project, I will take a quick look at Scoppy, as well as introduce two front-end shields that I have built for it.

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This is a short, three-part post, in which I will take a quick look at the Scoppy Oscilloscope and Logic analyser firmware for the RP2040, as well as introduce two hardware frontend shields that I designed to work together with it. I will be making use of my Raspberry Pi Pico carrier board as a base.

RP2040 Oscilloscope and Logic Analyser



Oscilloscopes and Logic analysers are essential instruments for every serious electronics hobbyist. They are however quite expensive, and thus beyond the reach of many people starting out with electronics. Today, I will show you a cheap solution, an RP2040 Oscilloscope and Logic analyser…

Before we get started, we need to clear up a few things first: 1). This is not my own project. It was designed and built by someone else. 2). This is not a professional grade Oscilloscope or Logic analyser 3). The range of input voltages, as well as the frequencies that you can measure, are limited.

What is this, and why do I bother with it?

This post is about the Scoppy Occiloscope Firmware, designed by fhdm-dev. I have no affiliation with him/her, I came across this recently and found it useful in the sense that it may help others gain access to instrumentation to greatly help them with electronics. I did design some derived pcb components that works with this project, in order to take care of some limitations that I saw in the original project. More on that in two follow-up posts, in which I will show you two PCB’s that I designed to use with this project, and analog Frontend ( based on a public design by fhdm-dev, as well as a Logic analyser shield, of my own design

before we do this, we need to look at the basic Scoppy design and its firmware.

Getting Started

You will need a few things to make use of this project, the most important will be the Scoppy App ( available from the Google Playstore ), and an Android Phone. You will also need a USB OTG Cable/hub for the phone, as well as a Raspberry Pi Pico or Pico W

The Installation and Getting Started Guide is very well documented, and as such, I will not spend a lot of time on that.

My own Setup

I have decided to use my own Raspberry Pi Pico Carrier board for this project, as it will allow me to get away from the breadboard, as well as serve as a platform for easily expanding on the project via expansion shields, as you will see in later articles.

Makeriot2020 Raspberry Pi Pico Carrier Board

This PCB, in Arduino Uno form Factor, will make putting the entire project into a case quite easy, as well as hopefully keep the number of floating hookup wires to a minimum. ( hopefully reducing some notice and other stray signals from interfering too much with our signals)

After installing the application, which is quite easy, we need to load the firmware onto the RP2040. This is also extremely easy is you follow the guide at the top. Please note that the Android app has two modes, a freeware mode, limited to one channel, and a paid version, with no limitations. I recommend that you consider buying the paid version, as it only costs a few dollars ( I paid $USD2), and will motivate the developer to keep working on the project, and improving it.

Scoppy Application, Main Interface – Oscilloscope
Scoppy Menu
Scoppy Logic Analyser Screen

As we can see, the interface is quite clean, and easy to use.

What are the limitations?

There are quite a few limitations, namely frequency and voltage input. From what I can understand, the frequency limit seems to be around 25Khz, with the voltage level limit being 0.0v to 3.3v ( as per the limit of the RP2040 ADC

Please make sure that you follow all instructions on the original page, as you can very easily damage your Android device as well as the Pico if you apply a voltage outside of the allowed range. On the logic analyser side, It is also important to note that you should stay in the 0.0v to 3.3v range of the Pico GPIO’s.


While these limited ranges will definitely limit what you can do and measure, It will still be a very useful project. In the next part of this article, I will show you how I have solved the logic analyser voltage range issue… Allowing you to analyse 5v signals as well.

  • Adding an Analog Front-end shield

    MakerIoT202011/27/2022 at 05:48 0 comments


    RP2040 Scoppy Oscilloscope Analog Front End Shield



    This post will look at my prototype Analog front-end for the Scoppy RP2040 Oscilloscope. It is important to state right from the beginning that this circuit is one of the 5 recommended designs from the Scoppy Website. I have only moved it from the breadboard design as published, onto a PCB.

    The entire circuit, with all of the original designer’s writeups, is available here


    So, why use someone else’s circuit? Well, the reason for this is two-fold. 1) The circuit designer also designed the firmware, so it stands to reason that his circuit will be optimised for use with the firmware. 2) Using his circuit provides a solid reference, making it possible to test the firmware for correct operation, and later on, providing a base for my own design – if and when I do decide it is worthwhile to actually design my own. As I already have a proper oscilloscope as well as a logic analyser, this entire exercise is purely academic, I find the Scoppy project interesting, and as such, I would like to see how it compares with my commercial products ( while also knowing that it won’t be a very fair comparison ). With all the limitations, I am however still quite impressed at the level of use that you can get out of this very simple device. It is definitely quite useful for a beginner.

    What is on the PCB, and what did I change?

    The PCB is a dual-layer shield that is designed to be used with the MakerIOT2020 Raspberry Pi Pico Carrier board. The shield is directly powered by the carrier board. The original Analog Front-End #3 circuit featured a single channel input, capable of accepting a -18.0v to 18.0v signal input. My changes were limited to doubling up on that circuit, to provide two channels.

    The Schematic

    Schematic_Pi-Pico-Scoppy-AFE-Circuit-3_2022-11-27-1Download

    I have redrawn the original schematic, partly to make it easier to understand for myself, as well as to help me with the design of the PCB. Lets take a look at the schematic ( by using text from the original designer) The author makes no warranty, representation or guarantees regarding the suitability of this design for any particular purpose. Nor does the author assume any liability arising out its use and specifically disclaims any and all liability, including without limitation special, consequential or incidental damages. All text below is quoted from here


    This design builds on Design 2 and adds over and under voltage protection to the analog front end. After all, we won’t have a cheap oscilloscope if we keep frying our components!

    I’m assuming here that the minimum and maximum voltages that will be applied to the input of the scope will be -18V and +18V respectively. It has been tested from -18.5V to 18.5V (two of my 9V batteries in series) but of course If you decide to use this design you are doing so at your own risk. I personally wouldn’t use Scoppy with an expensive phone/tablet just in case something unexpected goes wrong (better to use an old, obsolete phone that is no longer used for anything else) – especially when dealing with higher voltages – but of course you can do what you like.

    Protecting the Op-Amp input(s)

    First of all we need to protect the op-amp. In this design we’ll be using an LM324 op-amp, which is very similar to the LM358 but contains four individual op-amps rather than two. We’ll be using three of these op-amps. The reason for this will be explained later.

    According to the datasheet for the LM324 the allowed input voltage range goes from -0.3V to 32V. Of course 32V is above the maximum expected voltage (18V) and so we don’t need to worry about over-voltage protection. However we do need to ensure that the voltage at the input pins don’t go below -0.3V. A schottky diode can be used to clamp the voltage to something above -0.3V (D1 in the schematic).


    One thing that needs to be considered when selecting the diode is its reverse current. The 1N5817...

    Read more »

  • Adding a Logic analyser Shield to enable the use of 5v signals

    MakerIoT202011/27/2022 at 05:47 0 comments

    An Easy RP2040 Logic Analyzer Shield – Scoppy Scope Part 2



    As part two out of a series of three articles (part 1), This is the Scoppy RP2040 Logic analyzer shield, for use with our Raspberry Pi Pico Carrier board and the Scoppy Oscilloscope firmware for the RP2040.

    In Part one, we took a very quick look at the installation of the firmware, as well as the basic limitations for use of this very useful project.


    In this part, I want to take a quick look at my Logic Analyser shield, for use with this project, as well as the Raspberry Pi Pico Carrier Board. In part one, we saw that the logic analyzer inputs are limited to 3.3v by the RP2040 GPIO pins. This shield is a prototype attempt to overcome those limitations by using logic-level conversion.

    What is on the PCB ?

    The PCB is designed to be an add-on shield for the Makeriot2020 Raspberry Pi Pico Carrier Board. (Get your own here) It is in the same form factor as the Arduino Uno shields, but with pinputs specific to the RP2040 and Raspberry Pi Pico.

    8 Ch Logic analyser Shield for use with Scoppy and MakerIOT2020 Pico Carrier Board

    All Raspberry Pi Pico pins are broken out and labelled, as well as all of the pins specific to the Scoppy App have been clearly labelled. The board are stackable onto the Pico Carrier board, via standard 2.54mm Male Headers, or extra long, stackable female 2.45mm headers, similar to those found on common Arduino shields. The use of stackable headers will allow simultaneous use of the logic analyser shield and the Analog frontend shield, introduced in part 3 of this series.

    In addition to that, a 2×8-way 2.54mm Male header provides access to the 8 logic converted logic analyser inputs. Logic conversion is done with a simple circuit, comprising a Bss138 N-Channel Mosfet and two 10K resistors per channel. The shield is powered directly from the Pico Carrier board, which is in turn powered from the OTG cable to the Android Phone or tablet used to display the captured data. ( see Part 1 for installation instructions and other details regarding the Scoppy Project)


    The logic level converters allow the use of a 5v logic signal, which is an improvement over the original design, which allowed only 3.3v inputs.

    The Schematic and PCB Layout

    Logic analyser shield schematic

    Schematic_Pico-Logic-Analyser-with-Level-Shifted-Inputs_2022-11-25-1Download

    PCB Layout

    Manufacturing

    The PCB for this project has been manufactured at PCBWay. Please consider supporting them if you would like your own copy of this PCB, or if you have any PCB of your own that you need to have manufactured.

    PCBWay

    Some more pictures of the device

    Front
    Back
    Assembled Front
    Assembled Back
    Logic analyser shield together with RP2040 carrier board
    Stacked view 1
    Stacked view 2
    Stacked with logic probes

    Installation instructions (repeated from Part 1)

    Scoppy Scope Installation

    All credits for the development of the Scoppy firmware goes to fhdm-dev. This shield is a modification made by MakerIOT2020, and thus belongs to me. In the spirit of the original project, It will however be released to the public as a free open-source project ( free as in free download, free schematic, free design ). The PCB manufacturing files will be made available for free at a later stage, or can be ordered from PCBWay from this link


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