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. Some other Arduinos may work, but they must have analog input pin A7. So, for instance, the Uno won't work.
Install the RF24 library from TMRh20,Avamander version 1.4.7 or greater.
Upload 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.ino first to reset the EEPROM. Then reupload 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 |
| 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 output PWM |
* see channel setting below
The output pins support PWM. This is controlled by the voltage on pin A7, which is usually wired to +5V. If you leave A7 unconnected, you will get erratic results. On the Nano V3, it is easy to wire A7 to +5V because the two pins are right next to each other. In most cases that's what you will do unless you really want to use PWM.
If the voltage on pin A7 is read at less than +5V, then a warning will be printed to the master serial console. Unlike other settings, this can be changed in real time without a device reset.
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).
Connect pin D6 to ground via a normally-open pushbutton switch.
This signal is available on D2.
Single 1/10 second blink following reset:
- If seen, radio is enabled and connected properly.
- 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. This status output is always enabled, regardless of it baing enabled/disabled as a code output.
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, you must reset the transmitter. Then use the '^' command to restart the 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 |
4 device IDs are supported, selected by jumpers on pins A4, A5. This does change the nRF24L01 radio transmit ID, but it is more relevant to the device functionality. 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.