HotPaw apps for iPhone and iPad

HotPaw Productions has been developing unique iOS apps since the Apple iTunes App Store first opened.

Signal Processing Apps:

Software Defined Radio

SDR icon rtl_tcp SDR

rtl_tcp SDR is an iOS app that turns your iPhone or iPad into a portable Software Defined Radio with a spectrum viewer and waterfall. The app allows your iOS device to connect, via the via the rtl_tcp network protocol, to a networked RTL-SDR USB peripheral, and listen to FM and VHF radio signals.
This app requires that you have an SDR device, such as an RTL-SDR, and also have an rtl_tcp server, or rtl_tcp compatible server, running on a system such as a Raspberry Pi 4 or Mac. (Please note that there are vendor supplied SDR servers that do not use the open source rtl_tcp protocols. This app is not compatible with those servers.)
This app does support connecting to an Airspy HF+ or HF+ Discovery via an hfp_tcp server, which is an example of an rtl_tcp compatible server.
This app can also connect directly to the Hermes Lite 2 QRP SDR transceiver (via UDP, no tcp server required). (SDR Readme).

FT8 Decoder icon FT8 Decoder

The FT8 Decoder app allows decoding FT8 8FSK modulated signals contained in externally provided audio from an SSB radio or SDR to your iPhone. The FT8 Decoder app can also synthesize the audio of FT8 messages, thus can be used to experiment with sending and receiving FT8 encoded signals. (ft8d readme)

Morse Code Apps

Learn and work with CW, a very traditional amateur radio mode of communication.

morse decoder icon Morse Code Decoder

The HotPaw Morse Decoder (a Universal app for both iPhone and iPad available from Apple's iOS App Store) translates International Morse Code and CW audio into text using advanced DSP signal analysis techniques. Includes a spectrum viewer and an optional narrow band audio filter. Now supports decoding up to 80 WPM. The HotPaw Morse CW Decoder app has been featured in an issue of ARRL Contest Update.

See the HotPaw Morse Code page for more detailed specifications.

New: The online Help file now includes many Helpful Hints for users who can't get the Morse Decode to start decoding at all. Please read this Help File if you are having problems.

morse code ringtone icon Morse Code Ringtone Maker

Morse Code Ringtone Maker can create ringtones containing your own customized Morse Code messages. Be different... don't bore people with yet another pop tune ringtone for your iPhone.

(* Apple does not allow custom ringtones to be installed directly to an iPhone from an app. Instead the ringtones you create using Morse Code Ringtone Maker need to be installed on your iPhone either using iTunes (on a Mac), or using the Garageband iOS app, which requires multiple steps to create and install a ringtone. See typical 3rd party instructions here and here.

Morse Ringtone Readme documentation.

Morse2Text icon Morse2Text

The Morse2Text converts Morse code tapping on your iPhone touchscreen into text. You can use this app to input text to your iPhone without looking at the display. Copy the text to use in another app, or email it directly from the app. Both straight key and an iambic keying mode are supported.


Text2Morse translates text into high quality Morse Code sounds. Configurable WPM and tone frequency.


MorseTest generates 5 character random letter groups from a configurable letter set and at a configurable WPM to help one learn to hear and receive Morse Code.

Morse Words

Morse Words randomly plays the 250 most common English words in Morse Code. Configurable WPM.

Morse Code Key

MorseKey is a Free app available from the App Store. Tap and it will generate an audio tone. Both straight key and an iambic keying mode are supported.

Musical Instrument Tuners

Many professional musicians prefer strobe tuners for their accuracy and speed of tuning, both in the practice studio and on stage.

Wikipedia describes strobe tuners as the "most accurate type of tuner".

The HotPaw Productions waterfall strobe tuners are far more accurate than a guitar tuner with just a needle indicator, or even with an LED strobe. With the HotPaw animated waterfall strobe display, even the slightest differences between the pitch that the microphone hears and the ideal pitch frequency, will immediately cause the waveforms to waver and move sideways as they cascade down a pitch syncrhonized strobe window, all in real-time.
HotPaw Productions was the developer of the very first strobe tuner app, AeroTuner for PalmOS; and the HotPaw inTuna Strobe Tuner was among the first 500 apps in Apple's iPhone App Store in 2008.

inTuna icon inTuna Strobe Guitar Tuner

The HotPaw inTuna Strobe Guitar Tuner for iPhone (available from Apple's iTunes App Store) is optimized for 6-string guitar tuning, and includes both a single strobe mode, and multi-strobe mode that allows seeing the tuning of multiple strings simultaneously. Supports 8 popular alternate guitar tunings, as well as a configurable concert A=440Hz frequency.

inTuna Strobe Guitar Tuner HD

The HotPaw inTuna Strobe Guitar Tuner HD is optimized for iPad (and iPad 2). It includes the capability of programming multiple sets of custom per-string intonations.

iChromatic icon iChromatic HD

The HotPaw iChromatic HD Strobe Tuner for iPad allows you to view 12 simultaneous strobe tuners with strobes for all 12 notes of the chromatic scale, easily visible on a piano key graphic, for fast, accurate and noise resistant tuning.

Also available from the App Store is the HotPaw iChromatic Strobe Tuner for iPhone.

non-strobe tuners:

watch tuner icon Watch Tuner

The HotPaw Chromatic Watch Tuner allows you to tune a musical instrument using just the microphone on your Apple Watch, (no nearby iPhone required).

Talking Tuner icon Talking Tuner

The HotPaw Blind Talking Tuner uses speech synthesis to speak whether a note the iPhone hears is in tune or not. Useful when you can't see your iPhone display for any reason.

Try the HotPaw A440 icon Bass Guitar Strobe Tuner, a FREE strobe tuner app in the iOS App Store. Tune all 4 strings of a string bass or bass guitar simultaneously.

Try it, and see if you agree that strobe tuners are the fastest and most accurate way to tune a musical instrument.

Music Apps

Sing inTuna icon Sing-inTuna

Sing-inTuna (Universal app for both iPhone and iPad available from Apple's iTunes iOS App Store). Quickly visualize whether you are singing or playing on key and on pitch in a scrolling graph. This app will graph the note you are singing on a musical grand staff, and color code your pitch accuracy (Green for on pitch, Blue for sharp, Red for flat).

music spectrum icon Music Piano Roll Spectrograph

The HotPaw Music Spectrograph is a Universal app for both iPhone and iPad (and available from Apple's iTunes iOS App Store).

Visualize sounds, almost as they might appear in a piano roll MIDI music editor. See musical notes (plus all their overtones) graphed to assist with music transcription. Hear sounds "stopped-in-time" using a vocoder re-synthesizer. The HotPaw Musical Piano Roll Spectrograph creates a real-time, scrolling, midi-pitch-centered, 12th-octave spectrogram, from microphone input, or from your device's music library. You can also pause audio recording to scroll back to review the previous 4 minutes of spectrogram history.
NEW in Version 1.4.0: New Middle-pitch filter to help remove many of the overtones, making it easier to see just the main note pitches in music. Also a new icon!
PLEASE NOTE: For many musical sounds, a spectrogram will show LOTS of overtones and harmonics, not just the note pitch frequency or frequencies.
The Music Spectrograph Readme documentation.
(blog post on version 1.2.1)
(screenshot)   (screenshot 2)

icon Music Pitch Spectrum

Music Pitch Spectrum is a real-time 12-th octave audio spectrum viewer for the iPad, which allows one to visualize where a sound, including it's overtones and harmonics, fall on the musical pitch scale.

icon Dance Metronome/BPM

Dance Metronome/BPM is an extremely (sub-millisecond) accurate metronome as well as a BPM/MPM measuring app calibrated for strict tempo ballroom dancing.

autoharp icon iAutoharp

The iAutoharp is an easy and fun to play virtual instrument for your iPhone or iPad. Just tap a chord button and strum to hear the sweet sounds of a 37 string musical instrument.

Basic Programming Apps

Basic app icon HotPaw Basic for iOS

HotPaw Basic (in the iOS App Store)

Write and run Old-Fashioned Basic programs on your iPhone, iPod Touch or iPad. HotPaw Basic for iOS is very similar to the popular Chipmunk Basic in BASIC programming language support and features.

The latest update not only includes basic functions, but support for graphics, sound, GPS location, MQTT messeging, and Bluetooth LE communications.

See the Basic Programming Page for lots of information about programming using the BASIC Programming Language and its history.

Square Dance

Square Dance Checkers icon Square Dance Checkers

Just a simple set of movable/rotatable square dance checker icons. Free, from the iOS App Store

Square Dance Music Player icon Square Dance Music Player

A music player for one square dance tip (patter + singing call) using music from your iTunes library. Includes independantly adjustable speed and pitch, plus auto-looping. Available from the iOS App Store

Other Apps

Braille Key Talk icon Braille Key Talk

The Free Braille Key Talk HotPaw Braille Key Talk app is a 6-key floating virtual keyboard for short messages. Copy, tweet, or SMS your text using Braille keyboard input, and with or without enabling VoiceOver accessibility.
Latest update now includes an iOS 8 Braille keyboard extension.

Olde Notes icon Ye Olde Notes

Ye Olde Notes is an old legacy-styled yellow note pad app.

Say Color icon Say Color

The Free Say Color app uses the iPhone's camera input to detect and speak the name of the color in the center of a virtual camera viewfinder.

HotPaw apps for macOS (Mac OS X)

morse decoder icon Morse Decoder

The HotPaw CW Morse Decoder for macOS is available from the Mac App Store. The Morse Decoder application translates International Morse Code and CW audio sounds into text using advanced DSP signal analysis techniques. The application includes a spectrum viewer plus an optional narrow band audio filter. Supports Morse Code decoding at speeds up to 80 WPM.
Morse Decoder Readme documentation.

SDR icon rtl_tcp SDR

The rtl_tcp SDR macOS app is a Software Defined Radio client. Connect, via the rtl_tcp network protocol, to networked RTL-SDR, Airspy HF+, HF+ Discovery, LimeSDR Mini, or SDRPlay RSP1A/RSP2 USB peripherals, Listen to FM and VHF radio signals. (rtl_tcp requires that you have SDR USB hardware, plus a server such as a Raspberry Pi 3).
In addition the rtl_tcp SDR app can connect directly to the Hermes Lite 2 QRP SDR transceiver via Protocol 1 UDP (no tcp server required).
SDR Readme documentation.

Compatible usb-to-tcp server software:

Music Spectrograph icon Music Spectrograph

See the HotPaw Music Spectrograph for macOS (and a screenshot) in the Mac App Store . The HotPaw Music "Piano Roll" Spectrograph for macOS creates a real-time, scrolling, midi-pitch-centered, 12th-octave spectrogram, almost as it might appear on a piano roll MIDI music editor for you Mac. See musical notes and overtones graphed againt a piano keyboard to assist with music transcription. You can also Hear sounds "stopped-in-time" using a vocoder re-synthesizer.

iChromatic icon iChromatic Strobe Tuner

The HotPaw iChromatic Strobe Tuner for the Mac is available from the Mac App Store. The tuner shows single, double, or 12 simultaneous chromatic tuner strobes, plus an audio spectrum viewer. Allows configurable custom intonations.

Guitar Tuner icon Guitar Tuner

A Guitar Tuner for the Mac. A version of the iPad inTuna Strobe Guitar Tuner (see above) for your Mac.

Talking Tuner icon Talking Tuner

Talking Tuner for the Mac.   An macOS version of the iOS Talking Tuner (for tuning when you can't see your Mac's display).

Misc Info:

Website on Programming in Basic on the Mac

Obsolete PalmOS/PalmPilot apps and info


HotPaw Productions also provides iPhone/iOS app and DSP development consulting services for technically challenging problems. HotPaw Productions was founded by Ron Nicholson, who was a member of the original Macintosh, Amiga, and N64 design teams, as well as one of the first PalmOS developers. Enterprise iOS apps co-architected by Mr. Nicholson include Wyse PocketCloud, which was once among the very Top Grossing apps in the Business category of the iTunes App Store. This work also led to being named as co-inventor on 3 granted U.S. patents.


Many of the HotPaw icons were created by LizDesign

HotPaw Productions was named after the antics of Furball 1998-2013 the furry cat.


A collection of Readme's and Help files for many HotPaw Production iOS apps.

Contact Hotpaw Productions


All HotPaw Production iOS apps are distributed in the hope that they might be useful, but WITHOUT ANY WARRANTY OF ANY KIND; not even the implied warranty of MERCHANTABILITY or FITNESS for ANY PARTICULAR PURPOSE.

Apple, iTunes, App Store, iPhone and iPad are registered trademarks of Apple Inc. in the U.S. and/or other countries.

EULA and Privacy Policy

HotPaw App EULA and Privacy Policy
HotPaw Site Privacy Policy