ESP32 emulator for LPT/parallel port printers
Very rough, but works well enough™
Hardcoded SSID, PSK, target TCP socket settings. This would be very easy to fix, if required.
Currently, one IRQ needs to be executed for each byte and the bits are read manually.
A while (true) reading from the pins and doing the handshaking might be better suited.
A FIFO-buffer should be implemented to buffer the data between the LPT and the TCP socket.
The buffers fill-level could/should be used to indicate the BUSY flag to the LPT host.
Maybe possible: The ESP32 has an I2S peripheral with a parallel input & DMA capability. This mode is meant to be used with 8-bit camera modules, but it might (maybe with a bit of external logic) be compatible with a parallel port. This would allow for very high speed data input into the ESP32. Needs investigation.
To capture data from historic/vintage machines without using actual printers.
The ESP32 will act as a LPT/IEEE1284 printer and send all received data over a raw TCP socket.
This socket can be terminated in DIY software, in CUPS (to generate .pdf files) or in a real network printer directly.
An ESP32 and some way to connect it to the DB25 or Centronics connector.
There are cheap DB25 breakouts available or you can wire your own connector.
Note: ESP32 are not really 5V-compatible. It still works when connected directly, but this is out-of-spec.
In a production setup, putting resistors of about 100 Ohms to 5000 Ohms between all the pins (except GND) is recommended. 1kOhm is probably a good value.
| Name | ESP32 Pin | LPT Pin |
|---|---|---|
| !Strobe | 13 | 1 |
| D0 | 4 | 2 |
| D1 | 14 | 3 |
| D2 | 27 | 4 |
| D3 | 26 | 5 |
| D4 | 25 | 6 |
| D5 | 33 | 7 |
| D6 | 32 | 8 |
| D7 | 18 | 9 |
| !Ack | 15 | 10 |
| Busy | 17 | 11 |
| Paper Out | 16 | 12 |
| Select In | 35 | 13 |
| !Line feed | 23 | 14 |
| Error | 22 | 15 |
| Reset | 21 | 16 |
| !Select printer | 19 | 17 |
| Ground | GND | 18 |
Update the target TCP host and port, the WiFi SSID and PSK in the source code before flashing.
PlatformIO is recommended, but the Arduino IDE with installed arduino-esp32 should also work (untested!)
The ESP32 will open a new TCP connection for each print job and close old ones after a fixed timeout of no data being sent.
Setting the TCP host/port directly to Port 9100 of a real network printer will work fine.
In theory, yes. None of the pins are fixed function.
This project requires a lot of GPIOs though and many of the GPIOs on the ESP32 have additional functionality like strapping pins and might lead to strange behaviour.
The current pinout in main.cpp was tested and works on a ESP32S Dev Kit C V4-clone from AZDelivery.
Open a serial console with 115200 baud to the ESP32.
Is the WiFI connection established successfully? You should see the ESP32's IP being listed.
You can uncomment the Serial.write() and Serial.flush() calls in the receive-loop to get the raw data dumped to your serial terminal.
On the parallel port, there are 2 lines called "SELECT", one is "SELECT_IN" (LPT pin 13), the other is "SELECT_PRINTER" (LPT pin 17). There are wrong pinout graphics on the internet! Don't get fooled!
Install CUPS and cups-pdf, visit CUPS configuration page at https://localhost:631, create a new printer of type "CUPS-PDF" and set it as the default.
Create /etc/systemd/system/printserver@.service containing
[Unit]
Description=Virtual IPP printserver Socket Per-Connection Server
[Service]
ExecStart=-/opt/printserver.sh
StandardInput=socket
StandardError=null
DynamicUser=trueCreate /etc/systemd/system/printserver.socket containing
[Unit]
Description=Virtual IPP printserver Socket for Per-Connection Servers
[Socket]
ListenStream=31337
Accept=yes
[Install]
WantedBy=sockets.targetand a shell script called /opt/printserver.sh containing
#!/bin/bash
lpr -T"`date`"Then run
chmod +x /opt/printserver.sh
systemctl enable --now printserver.socketand try to telnet 127.0.0.1 31337 and send some data.
After closing the connection, you should see a new file in /var/spool/cups-pdf (or an error message somewhere in the journal or CUPS log).