hpr-knowledge-base/hpr_transcripts/hpr4517.txt

Episode: 4517
Title: Cheap Yellow Display Project Part 4: The hardware 
Source: https://hub.hackerpublicradio.org/ccdn.php?filename=/eps/hpr4517/hpr4517.mp3
Transcribed: 2026-07-31 16:13:06 (official HPR transcript)

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This is Hacker Public Radio Episode 4517, for 2025-11-25
Today's show is entitled, "Cheap Yellow Display Project Part 4: The hardware "
The host is Trey and the duration is 00:11:19
The flag is Clean, and the license is CC-BY-SA
The summary is "Explanation of the hardware which will be used for this project"
hello again this is trey welcome to part four in my cheap yellow display project series
if you have hung in there with me so far on this journey thank you if you have missed earlier
episodes you can find them on my hpr profile page and there's a link in the show notes
if you have questions comments concerns snide remarks or other feedback please leave an episode
comment or drop me an email using the address in my profile even better you could record and
upload your own show which shares your viewpoint or expertise to review i finally have an actual
project to build using the cheap yellow display it is a portable programmable morse code key or memory
which can be connected to my hf transceiver radios by simply plugging it into the code key input port
then i could transmit stored messages by simply touching their specific icon on the touch screen
so now i purchased a pair of cheap yellow displays each arrived in an anti-static zipper bag with a
usb-c cable a six inch long four pin pb 1.25 millimeter to dupont 2.54 millimeter cable harness
a plastic case holding the cheap yellow display itself and a small plastic stylus there are
pictures in the show notes depending on how many i-o connections i may need and how i plan to power
this i am probably going to need more four pin pb 1.25 millimeter wired connectors you can see a
description of the various features and connectors on random nerd tutorials right up about this board
and there's a link in the show notes the only difference i can see between this description and
what is what i received is that mine have both a usb micro usb and a usb-c port on them
i'm going to include some pictures for you of course the first thing i had to do was plug it in and see
what happens as you can see in the pictures it appears to be running some kind of simulation of a website
the backlit display looks all right it's not super high resolution but for the price it will suit my needs
just fine the touch screen is responsive but remember it is pressure sensitive and it works best using the
provided stylus or a fingernail and not your fingertip all right so i have the cheap yellow display what
other hardware do i need well i need to address how one of these will actually connect to my radios
modern amateur radio transceivers which support continuous wave transmission which is another
name for morse code generally can use one of two different pieces of hardware for input
the first is what we call a straight key below is a photo of the one that i own
this is a classic old-fashioned telegraph style code key it is designed to quickly and easily be pressed
down to close a circuit and when released the circuit is opened effectively making it a normally
open push button switch to send a dot the operator holds down the key for a short period of time then
releases it to send a dash the operator holds down the key for a longer period of time before releasing
it we will discuss the actual timing specifications for morse code in a future podcast connectivity for the
switch has been standardized to use a 3.5 millimeter mono mail phone connector which has only sleeve and tip
connections the second option is a paddle style electronic keyer there are many styles of these and i'm
including a picture of the one which i use which also belong to a close friend of mine who is now silent key
in general the paddle is two separate normally open switches in the most common configuration when an
operator presses and releases the paddle on the right a dash is sent if the paddle on the right is held a
continuous series of dashes will be sent until the paddle is released the left paddle works similarly
if it is pressed and released a single dot will be sent if it is pressed and held a series of dots
will be sent until it is released the function of these paddles can be swapped from left to right
using the radio configuration there is additional functionality which can be configured in some radios
for when both paddles are pressed simultaneously but i am not going to describe these here
the paddle generally uses a 3.5 millimeter stereo mail phone connector with the sleeve being common
the tip of the connector is wired to the left paddle and the ring of the connector is wired to the right
paddle most common radios have a built-in keyer which can be configured for a paddle and will
automatically transmit dots or dashes at whichever speed is configured within the radio based on which
paddle is pressed you can see this phone connector illustrated on wikipedia's phone connector page
and i'm including a link in the show notes you can learn more about the various devices which can be
used for sending morse code and how they function at morse code world ideally controlling all the morse code
timing within the cheap yellow display would be best that way it could be connected as a straight key
and a any key or settings already configured within the radio should not matter however if i wish to
also be able to manually send morse code myself using my paddles without disconnecting the cheap yellow
display and reconfiguring the radio that could be problematic i may need to factor in the possibility
of connecting my paddle to the cheap yellow display as well and then building in code to respond to inputs
from the paddles as i mentioned in a previous episode i have an arduino nano on my desk as a practice
oscillator for my paddles i may be able to reuse some of the code on the cheap yellow display
i'm including a picture of that arduino nano circuit in the show notes
so if i want the cheap yellow display to appear to the radio like a straight key
i will need it to be able to control a switch quickly and accurately
but i also want the cheap yellow display and the radio to be electrically isolated from each other
here this calls for a relay i was able to find and order some inexpensive relay modules which work
nicely with arduino and esp32 and i'm including a picture in the show notes these allow connectivity
to a 5 volt power display or power source and to one of the cheap yellow displays gpio pins
these feed an octocoupler circuit which in turn drives the coil for the relay this provides inductive
kickback protection to the cheap yellow display and can drive a coil which will require more current than
the gpio is able to provide all right time for a rabbit trail an inductor is simply a coil of wire
direct current flowing through any wire generates a magnetic field within the inductor because the
wire is coiled the magnetic field builds from each pass of the wire in the coil if you include an iron core
it sustains the magnetic field even better this is the basis for an electromagnet you've probably played
with one as a kid a relay is simply a momentary contact switch controlled by an electromagnet
one unique property of an inductor is that current wants to keep flowing in the direction it was applied
to be specific when the current source is removed the magnetic field still exists for a while
and it effectively generates an electric current in the coil in the same direction as the one which
initially created the magnetic field to begin with if it has a path to flow the current will create
another weaker magnetic field which creates its own electric current in a diminishing loop if the
circuit which drives the coil of a direct current relay is not ready for this continued push of current
damage can be done many times this is countered by wiring a flyback diode in parallel with the coil
and in the opposite direction in which the current will be applied this way when the current source is
stopped the diode gives a pass for the inductive kickback current to safely flow while the magnetic
field dissipates i'm going to include a link in the show notes that explains this in greater detail
all right back to our topic the switch side of the relay is a single pole double throw and makes
connections available for common normally closed and normally open
it will be easy to connect the common and normally open connections to a 3.5 millimeter mono mail phone
connector so that it may be plugged into the keyport on any radio transmitter i will need to do some
testing on the speed of the relay but i think it will work just fine once i start writing code for the
cheap yellow display i will be able to connect and test the relay
all right this is a good place to end this episode and it is one of the longest in this series so far
in the next episode we will begin to look at how we design the user interface for our program
something i do not know anything about just yet stay tuned weekdays for additional exciting episodes of
hacker public radio and at some point the next episode in this series
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