An Arduino sketch that converts text to Morse code and other formats, outputs to GPIO, and can transmit message to slave devices using an nRF24L01 radio.
It can store up to 4 different messages of up to 240 characters each (selectable by jumpers.)
This project was developed using the Arduino Nano V3, and a compatible board with integrated nRF24L01 radio.
Arduino Uno will work, but lacks support for PWM output.
Install the RF24 library from TMRh20,Avamander version 1.4.7 or greater.
Upload morse/morse.ino. The sketch will work initially with Arduino factory settings (EEPROM set to all 0xFF). If it is a used Arduino, the safest thing to is, upload eeprom_reset/eeprom_reset.ino first to reset the EEPROM. Then reupload morse/morse.ino.
If using an external radio, wire CE to pin 10 and CSN to pin 9. This sketch supports integrated boards, and that's what they use. Note this is reversed from what it says in most online sources.
The output pin is D5 and the inverted output is D3.
Many behaviours of the device are determined by jumper wirings to ground on various GPIO input pins. See below for the details of each of these. Jumper settings are only detected at setup (reset) of the Arduino.
Here are the descriptions of each pin. All INPUT_PULLUP pins are active-low according to the function described:
| Pin | mode | function |
|---|---|---|
| D2 | OUTPUT | error/status signal |
| D3 | OUTPUT | inverted Morse signal |
| D4 | INPUT_PULLUP | disable radio |
| D5 | OUTPUT | Morse signal (PWM) |
| D6 | INPUT_PULLUP | code key switch |
| D7 | OUTPUT | secondary output |
| D8 | INPUT_PULLUP | slave (receiver) mode |
| D9 | SPI | CSN to external radio |
| D10 | SPI | CE to external radio |
| D11 | SPI | MOSI to external radio |
| D12 | SPI | MISO to external radio |
| D13 | SPI | SCK to external radio |
| 3v3 | power | to external radio |
| A0 | INPUT_PULLUP | radio power, bit 1 |
| A1 | INPUT PULLUP | radio power, bit 0 |
| A2 | INPUT_PULLUP | radio channel select* |
| A3 | INPUT_PULLUP | radio channel select* |
| A4 | INPUT_PULLUP | device ID, bit 1 |
| A5 | INPUT_PULLUP | device ID, bit 0 |
| A6 | unused | |
| A7 | INPUT | sets PWM (Nano only) |
* see channel setting below
Ensure that the board is set correctly at compile time.
On boards that support analog INPUT pin A7 (such as the Nano), we support PWM output on D5. The pulse width is controlled by the voltage on A7, and it is enabled by default. On boards (such as the Uno) that do not have this A7 input, it is disabled by default.
Support for A7 is detected at compile time depending on the characteristics of your board. On boards that do have it, PWM is enabled by default. If you do not want to use this feature, then either:
- (Recommended:) Physically wire A7 to +5V (neighbouring pin). If A7 is left floating, you will get erratic results, and a warning is printed to the serial console at run time.
- Define MORSER24_NO_PWM at compile time, by by editing
platform.local.txt(in the same directory asplatform.txt, typically~/.arduino15/packages/arduino/hardware/avr/1.8.6/for AVR boards) and addingcompiler.cpp.extra_flags=-DMORSER24_NO_PWM
If using PWM, connect A7 to a voltage divider. Unlike other settings, the pulse width can be adjusted in real time without a device reset.
Connect pin D6 to ground via a normally-open pushbutton switch.
Connect a red LED from pin D2 via a current-limiting resistor to ground. This is used to indicate error and operating conditions (see below).
This signal is available on D2.
Single or double 1/10 second blink following reset:
- If seen, radio is enabled and connected properly:
- single blink: Device is in master mode.
- double blink: Device is in slave mode.
- If not seen, radio is disabled.
Continuous fast blink:
- Radio is enabled but not connected properly.
Solid red:
- Slave mode is enabled and the radio is disabled. This is an unsupported configuration.
Short blink during message display:
- Invalid character in the message. (* will also be printed after the character in the serial monitor.)
Pin D7 serves two functions: As a code output, and a status output. In most cases you would connect it to a buzzer, which helps to monitor the unit if (say) it is located in another room.
-
As a code output, it is turned off normally. It is enabled and disabled using the '>' commands (see message entry below.) This setting is persisted to the EEPROM. This output does not use PWM.
-
As a status output, in case of an error that activates the primary status output on D2, pin D7 is also activated. This helps to alert on error conditions.
Pressing and holding the pushbutton enters manual mode. The button will subsequently act as a code key for manual input.
In order to exit manual mode on the transmitter, you can reset it; but this will not resume message display on the receiver. To do this, either enter a new message, or use the '^' command to retransmit the message and restart display on the receiver.
If not using a radio, see standalone mode below.
The nRF24L01 supports wireless channels 0-125. morseR24 supports 4 channels, from 88 to 118 in increments of 10. The channel is specified using jumpers on pins A2, A3. If none of these are wired to ground, the channel defaults to 118.
Wiring chart:
| A2 | A3 | radio channel |
|---|---|---|
| - | - | 118 |
| GND | - | 108 |
| - | GND | 98 |
| GND | GND | 88 |
A utility freqmon/freqmon.ino is included to identify channels with potential interference.
Configured by jumpers on pins A4, A5. This selects both:
- The nRF24L01 radio transmit ID
- The message/settings bank in use (see message entry for more details)
The radio power is set by jumpers on pins A0, A1.
| A0 | A1 | radio power |
|---|---|---|
| - | - | MAX |
| - | GND | HIGH |
| GND | - | LOW |
| GND | GND | MIN |
If not using a radio:
- Wire pin D4 to ground
- Leave pin D8 unconnected
- Refer to message entry below.
For master mode, leave pin D8 unconnected.
Simply starting or resetting the master will not initiate a transmission and does not update the message displayed by the slave, even though the master may be actively displaying a message. So it is possible for the two devices to be out-of-sync.
It is possible to store up to 4 messages. The message bank in use is determined by the device ID setting on pins A4, A5.
Connect to computer via USB.
To transmit (synchronize) the current message from the master to the slave, use the ^ command.
To enter a new message, input text in the serial monitor console. The maximum message length is 240 characters. It accepts multiple lines (as the serial input buffer can only accept 63 characters at a time) and concatenates them together. The partial message is displayed followed by a '<' symbol indicating that more text can be entered. Enter a blank line to commit the message.
The following in-line characters will cause the text to be interpreted in several different ways:
- Morse code (the default, or preceded by an underscore _ )
- Unary (using the # character). For example, #314159
- Hexadecimal (using the $ character). For example, $600DF00D
- Chess coordinates (using the % character). For example, %e2e4 e7e5
You can change these in-line modifiers mid-text.
The following commands entered on the serial monitor allow manual control of the output pins, without erasing the current message:
- ^0 turns the GPIO output D5 off, and inverted D3 on
- ^1 turns the GPIO output D5 on, and inverted D3 off
- ^ sync slave with master and resume display
(To resume display on the slave without retransmitting the message, you must reset the slave.)
The following commands allow control of data output to pin D7. This is initially disabled; but if enabled, it provides another copy of the Morse output. This is useful, for instance, using a buzzer in another room for troubleshooting.
- >0 turns output follower off
- >1 turns output follower on
This setting is persisted in the EEPROM and will persist over a device reset.
The timings can be changed using the "star commands." For example:
- *s100 changes the dot length to 100 ms
- *p3000 changes the inter-message pause to 3000 ms
The command will be transmitted to the slave. Issuing one of these commands will interrupt and restart any broadcast in progress.
For slave mode, wire pin D8 to ground.
The serial monitor will display the characters as they are output, as well as any speed and pause timing changes.
Here, an LM555 timer in astable mode generates a tone that is sent to a mono audio jack. The output on pin D5 is sent to pin 4 (active low reset) of the LM555 to modulate the signal. This example uses a Nano V3 (compatible) with external radio connected to the SPI bus. This circuit can be used in master mode (with or without radio) or slave mode.
This example uses an integrated Nano V3 + nRF24L01 board. It is configured as a slave. Here, the output D5 (green) drives the gate of an IRF540N MOSFET in open drain configuration, that can then be used to control an external circuit. The 3-terminal connector provides access to the MOSFET drain (brown), unregulated power from the barrel jack (orange), and GND.
Similarly, the inverted output D3 could be used to drive a P-channel MOSFET such as the IRF9540.
By utilizing test mode, a device A running morseR24 can be used as an auxiliary radio from a secondary device B running different code. See aux for a simple example.