The ability to generate a clean sine wave is incredibly useful to the
electronic home-brewer. In testing a an audio or RF circuit you often
need a tune-able, stable frequency source. Commercial ones range from
very expensive, with the ability to generate arbitrary waves at very
precise signal levels. For my purposes a simple sine wave generator
with a variable attenuation meets most of my needs.
This Signal Generator is built using an AD-9850 Direct Digital Synthesizer
and an Arduino Nano. It generates a clean sine wave from 0 to 62.5 MHz
(very clean up to about 50 MHz, but still use-able up to 62.5. There
are various versions of this floating around the internet, including
prebuilt ones from a variety of sellers. The display is
16x2 I2C LCD. The control is a Rotary Digital Encoder with push button.
Turn the encoder
to change frequency. Push the button to select the tuning increment.
There are various versions of this floating around the internet. This is my implementation.
The code and build instructions are available on Github at:
To control the AD-9850 I chose to use a DDS library written by Paul Darlington, M0XPD. You'll need to download it from his Github repository and install it using the Arduino IDE Library Manager. You can read Paul's original blog for details on the library.
DDS Signal Generator Module - any one of the AD9850 boards should work. I used each of these at different times:
Mounting hardware - 4-40 standoffs and spacers, machine screws, washers and nuts
0.1" female headers on the breadboard make it easy to wire the components up in the case
Signal Generator Construction
And here is what the finished product looks like:
KK4DAS Signal Generator
I've been using this in my shop over the last few months to test out circuits on the Furlough-40. It's really useful to be able to inject a known signal at various points in the circuit and see now the downstream amplifiers and filters perform Highly recommended!
At a recent meeting of the Vienna Wireless Society I demonstrated how straightforward it is to build this. I went from a pile of parts to a working unit in under an hour. Here is the video from the meeting:
I've been working steadily on the revising the Arduino code for the Furlough 40 Homebrew 40 meter SSB phone transceiver that I built earlier this year based N6QW, Pete Juliano's Simple SSB. Last time I described the code for a color TFT module to use as a replacement for the 4x20 LCD that I originally used and I promised to upload additional modules. The code for a fully functional ham radio control program is complete. I need to finish documenting it and will post it to my github page. In addition to the display module already posted I plan to post on each of the remaining modules required to produce a fully functional SSB control program including the SI-5351 produced LO and BFO clocks. This control program should be straightforward to adapt to a variety of homebrew radio projects. The modules that I will be provide and document are:
Display Modules
TFT Display
Nextion Touch Screen Display
4x20 LCD Display
Button Handler (hardware buttons and switches)
Encoder - handles the rotary encoder and push button
While I was putting the final touches on the CAT control code for the F40 I received an email from Pete asking me about programming a Nextion Touch Screen display. I had a spare in the junk box. I had purchased two when I upgraded my uBix V6 to the wonderful uBitX Nextion module provided by KD8CEC, Ian Lee. That upgrade was plug and play since KD8CEC provided all the code. When I got Pete's email I loaded up the Nextion IDE and cobbled together a "LED On, LED Off" sketch which is the Arduino version of "Hello World." The Nextion IDE and programming library are available for free on the Nextion web site. It requires a bit of fiddling and a learning curve to get it going and I will fully describe in a future post. I sent off the code to Pete and he asked about how to include a frequency display. I did that in about five minutes and that inspired me to try to build the F40 user interface. Since I had recently completed the TFT Display Module I already knew what functions I needed to implement for display side of the interface. As a reminder, the display functions are things like:
DisplaySetup
DisplayActVFO
DisplayAltVFO
DisplayVFOAB
DisplayTxRx
DisplayMode
DisplayIncr
DisplayTune
One of the cool things about the Nextion IDE is that it allows you to build and simulate what you will eventually see on the screen - and it is all drag and drop with very little programming is required. The Nextion communicates with Arduino Sketch via a simple protocol running over a serial interface.
Since I already had two working display modules built (for the 4x20 LCD, and for the color TFT) I already knew what I needed. Within about two hours I had fully reproduced the functions of the color TFT display. Buttons and switches are also easy to implement; a couple of hours later I had reproduced the front panels switches from the F40 - VFO A/B, LSB/USB, and TUNE. That was another couple of hours. So in about half a day I had created a fully functional touch screen display for the F40. The only physical change to the F40 was disconnecting the LCD and connecting two wires to the Arduino plus power. Not bad at all!
Based on that success I began work on extra features that I had put off adding to the F40 because they would require either complicated menus or a bunch of other hardware buttons. The first thing I added was the ability to work Split (transmit on one frequency and receive on a different frequency). One button (five minutes) - and about 30 minutes to write the code on the Nano to switch the clock frequencies on the SI5351. I previously described my approach to modular programming and since I had already written the VFO/BFO control module it was a matter of a few minutes to code that up. I then added a Scan button to scan through frequencies and this was interesting - I was able to add that function by just making changes on the Nextion - no Arduino programming required.
More on Nextion programming later - but for now, please take a look at the video and let me know what you think in the comments.
APRS and the International Space Station
KM4HRR Talks to the ISS
On Sunday, my friend KM4HRR Brendan invited me to see the progress he has made in contacting the ISS using APRS. His setup is the following:
Kenwood TH-D74 Transceiver, with an ISS profile that he created
At about five minutes before the pass, ISS Detector sent an alert. Then, using the iPhone camera, also controlled by ISS Detector, he pointed the antenna at the horizon. Right on time, he received an APRS beacon from ISS and over the next few minutes Brendan sent and received several APRS messages. He had added several macros to his ISS profile on the TH-D74 to make it easy to send messages during the 5-6 minute pass.
All in all, a pleasant way to to spend and hour. I now may have to invest in an APRS capable HT!
Farewell Neowise, we barely knew ye....
In keeping with the space theme, when I am not playing radio, I play photographer - and here are two of my favorite captures of comet Neowise at nearly its closest approach to earth.
I wanted to liven up the display module for my F40 - the 4x20 LCD display is certainly functional, but decidedly industrial in look. I have gotten quite fond of the color display on my uBitx, so I decided to build a color display module for the F40. I opted for a color TFT for the display since they are ubiquitous, inexpensive and there are many good Arduino libraries that make programming a snap. Uber Elmer N6QW, Pete Juliano graciously shared with me the sketches he had written for various color TFT projects and I downloaded and also evaluated sketches from several other hams. Not quite finding what I wanted, I decided to write my own sketch.
I should let you know that I'm a relatively young ham (60 years young, but licensed only two years ago), but I am a very old software guy (still 60, but have been a professional software engineer and executive for 40 years). So, when I started looking at source code for Arduino sketches that were written by amazing hams with no formal software training I knew I had to dive in.
My design goals for the project were the following:
The code must follow sound software engineering principles throughout.
It must be modular and reusable. To be easily reusable the code most not be dependent on any particular hardware design. You should be able to drop it in to any Arduino based radio control program with minimal effort.
It must have a small memory foot print and not use up much of the Arduino's precious dynamic RAM.
It must be fast and not tax the Arduino microcontroller- we want to save its CPU cycles for control of the rig.
It must use standard Arduino display libraries and be relatively hardware independent - easy to port to a different display or microcontroller.
It must be easily reconfigurable - you should not have to change code to make simple user interface changes like screen colors and font sizes.
It must provide the basic display functions for a dual VFO SSB rig - and that means dual VFO display, active VFO indicator and LSB/USB indicator.
It must be easy to add new display elements - including an S meter and other similar displays.
And last, the code must be easy for a non-professional coder to understand and work on. No tricks or fancy code footowork.
So, over the long memorial day weekend I wrote and tested the KK4DAS SSB TFT Display.
A quick note if you are interested in building this. This is not a complete radio control sketch - it is only the display module. Over the coming weeks I will publish additional modules that will implement a complete SSB transceiver controller. But for now, all you need is an Arduino and a color TFT, and possibly some level shifters. The Arduino nano uses 5V logic but the TFT needs 3.5V logic so the level shifters are used to take care of that. You'll also need to install the Arduino IDE and load the two required libraries.
Here are some of the details:
Features
Basic radio display panel for an SSB transsceiver
Designed for a 320x240 Color TFT (non touch)
Tested with an ILI9341 display
Requires the following libararies
Adafruit_GFX
Adafruit_ILI9341
Implements a basic SSB display console with the following features
Dual VFO A/B
Mode indicator SSB/LSB
Tx/Rx ndicator
TuningStep Inidicator
S Meter
Banner including Call sign
Fully customizable. Fast display makins use of minimal resources./
Room is left on the screen for additional features
There is room on the screen for another row of features
Easily change colors, font sizes and layout
Default Screeen Layout
____________________________________
| A 7.200.000 LSB | -- VFO A/B indicator, Active VFO Freq, LSB/USB inidicator
| Rx 7.048.000 100K | -- Rx/Tx indicator, Alternate VFO Freq, Tuning Increment
| |
| S |_|_|_|_|_|_|_|_|_|_|_|_| | -- S Meter
| 1 3 5 7 9 |
| |
| AGC SPL RIT | -- (Planned) AGC on/of, Split On/Off, RIT On/OFF
| |
| Ver Rig Name Call |
|___________________________________|
This module provides the following radio console display functions:
displaySetup - initialize the display and displays the startup values - call once from your setup function
displayBanner - Displays a text banner across the bottom of the screen
displayActVFO - Displays the frequency of the Active VFO
displayAltVFO - Displays the frequency of the Alternate VFO
displayVFOAB - Displays the indicator which VFO is active (A or B)
displayTxRx - Displays whether the rig is in (Tx or Rx)
displayMode - Displays the which sideband is selected (LSB or USB)
displaySMeter - Displays the S Meter (1-9 are gray, +10 +20 and +30 are red
This module also provides the following general purpose display functions:
displayClearScreen - fills the screen with the selected backgrond color
displayPrintat - prints text or nubmers on the screen at a specific location
displayDrawBoundingBox - draw a box on the screen and fills it with a background color
displayDrawTextBox - displays text inside a boundig box
Design notes and how to use the code
NOTE TO BUILDERS
This is not a complete radio control sketch. It is the Display software only. In the spirit of modular design
it is stand-alone and not dependent on using an SI-5351 or any other specific hardware, or on my particular
hardware selection of switches, buttons and knobs. The demonstration sketch shows how to update the display, but you need to provide the code to determine what the actual values should be. You will likely need other
libraries like the Si5351 and a Rotary encoder library aside from the GFX and the ILI9341.
DESIGN PRINCIPLES
Good software design principles are to use as few hard-coded numbers as possible. Wherever possible I have used #defines for any number that will be used more than one place in the code. For example #define DSP_VFO_ACT_X 60 defines the X coordinate (how far from the left of the screen)
of the Active VFO frequency display. You will see multiple references to DSP_VFO_ACT_X throughout the code,
but I never use the hardcoded number 60 again. Change it once – and it is changed throughout.
Taking the S-Meter as an example:
To update the S-Meter display you make a call to displaySMeter(n); where n is an integer from 1 to 12
(representing S1-9, +10, +20 +30). Your sketch will need a way of monitoring signal strength (an analog input
pin on the Arduino attached to an appropriate place on your rig) and converting it to the logarithmic S scale.
SCREEN COORDINATES
Coordinates work differently on displays than a typical graph where the origin 0,0 is in the middle abd positive
and negative values move you away from the origin. For displays 0,0, the origin, is always upper left hand corner
of the display and you only use positive numbers for the coordinates +X is pixels from the left edge, +Y is pixels
down from the top. This particular example based on a 320x240 display but should be easily portable to other
display sizes – but you have to keep in mind how the coordinate system works.
SCREEN LAYOUT
Here are a few notes about how the demonstration display is laid out. This should help you understand the design
concept and allow you to begin to modify it.
The VFO display is setup for a dual VFO rig. The currently Active VFO is always on the top and the alternate VFO
is just below it. Your code will need to keep track of whether VFO A or VFO B is currently selected and call the
display routines to update the display. I’ll describe how the VFO displays are are defined and that will give you
an idea how you might modify or enhance the display.
Active VFO - top center of the screen
#define DSP_VFO_ACT_X 60 // Active VFO begins 60 pixels from the left hand edge (I picked 60 by experimenting)
#define DSP_VFO_ACT_Y 30 // Active VFO box starts 30 pixels down from the top of the screen
// (Try changing it to 50 and see what happens)
#define DSP_VFO_ACT_COLOR ILI9341_GREEN // This sets the text color for the Frequency display. Use whatever colors you like
#define DSP_VFO_ACT_BK ILI9341_BLACK // This sets the background color for the Active VFO
#define DSP_VFO_ACT_SZ 3 // This is text size from Arduino TFT, values 1-5 1 is small 5 is large (2 was too // small, 4 was too large, 3 was just right)
Alternate VFO – the second VFO is placed directly below the Active VFO on the screen.
There are a couple of things of interest here. For the X coordinate, instead of putting in a hard coded number I refer back to
the #define that I used for the Active VFO (DSP_VFO_ACT). That way, if I want to move VFO section to a different part of the
screen I only need to change one number DSP_VFO_ACT_X, and the alternate VFO will move as well. Figuring out the Y coordinate
for the alternate VFO is a little more challenging. Some math is involved. Starting with the Y coordinate of the Active VFO
I need to calculate where how far down the display I need to go to place the second VFO. To do that I need calculate
how many pixels tall the text characters in the Active VFO are and use that as an offset. It turns out we have everything
we need already defined. CH_W and CH_H are #defines that specify the height and width of a text character in pixels for
TFT font size 1. Size 2 through 5 are even multiples of that – so font height for size 2 is
2*CH_H pixels and font width
And for size 4 is
4*CH_W
pixels and so on. so we have everything we need to calculate how many pixels the Active VFO takes
on the screen – we multiply the font size by the character height and add 16 pixels offset. The 16 was determined by
experimentation for something that looked good. The code looks like this:
Take a look the other sections of the display code and you will see similar references and calculations. The VFO A//B
indicator and LSB/USB mode indicator, for example are similarly “pinned” to the Active VFO display, so if you move the
Active VFO display to another screen location they will move also.
In summary - each object is on the display is defined by a set of constants that indicate the X,Y coordinates
of the object on the screen and various other attributes like text size and color. The basic user interface display
object is a bounded/filed text box. You can control the text size and color, and the box fill color. With this basic
set of features you can implement a wide variety of user interface elements. The S-meter, for example, is a row of
filled boxes.
HARDWARE NOTES
My test sketch uses an Arduino Nano. The display is an HiLetgo 2.2 Inch ILI9341 SPI TFT LCD Display 240x320,
but any ILI9341 display should work. There are many sources. Please note that the Arduino has 5V logic levels,
but the display requires 3.3V - so you need some sort of level shifter. I used the"HiLetgo 10pcs 4 Channels IIC I2C
Logic Level Converter Bi-Directional 3.3V-5V Shifter Module for Arduino" I used hardware SPI and the pinouts are
standard as follows:
Arduino
Pin TFT Pin
-----------|---------
8 | RST - any free Arduino Pin (not used in this sketch)
9 | DC - any free Arduino Pin
10 | CS - any free Arduino Pin
11 | MOSI - fixed
12 | MISO - fixed
13 | CLK - fixed
That is all the wiring you need for the demonstration sketch.
