Raspberry Pi Forums

Hi all,

Is it possible to tap in and read what is being displayed on the LCD of separate device?
i.e. scales, electric thermometer, digital watch, digital radio.
If yes, how could I go about doing this.

Thanks,

Wayne

Thank you for the link. I was hoping for of something more along the lines of signal recognition rather than optical.

I would like the raspberry pi to act as a virtual LCD to another device.

Anyone?

can you explain what you want more

fortisvir wrote:Anyone?

Apparently not!

I don't have a clue either, but this is how I would tackle it. No claim that it is the only or best way.

First I would get a cheap LCD display like a Nokia 5110 and learn how to interface that to my RPi, to understand what sorts of signals are applied to the module to generate a display. [I know this isn't your aim - this is for getting background knowledge.) Example here.

Then I would set about disassembling and hacking a still working device with an LCD display. (There is a serious risk it won't be working after it has been hacked!) Finding a datasheet for the display device would be bonus.

If you can break out ( = tap into ) the connections to the display you might be able to convert the signal levels to gpio levels and connect them to appropriate pins on the RPi. Then you could use something like @joan's piscope to watch the waveforms of the signals being sent by your original device. Once you can see those then, with the help of the datasheet to interpret them, it might be possible to write a simulator for the display. You might strike lucky and find that the display uses a 'well-known' protocol like SPI or I2C for signalling, in which case there are existing library modules that will have done some of the hard work for you.

Interesting project! Good luck.

Have you made any progress with this? I am interested for a similar project. I would like my RPi to capture and pass on to a wireless device, the contents of the LCD for my 3D printer.

The printer is based on the mighyboard , schematic https://www.thingiverse.com/thing:16058 . The best answer from the 3DP world i have recieved was " However, the LCD modules put in MakerBots and their clones are not I2C. They all follow the Hitachi HD44780. It's still hackable with a RPi or other uprocessor. Just not I2C. Have the RPi just be a serial relay: eats the data for the Hitachi, regurgitates it to the Hitachi, and also squirrels it away for whatever other nefarious purposes you have in mind."

I have found many resources for writing to a screen, but nothing for reading

The idea of 'serial relay' is to put your RPi in the middle of the writing device and the display - basically cut the wires, plug the ones coming form the device to RPi 'inputs' and connect RPI 'outputs' to the display, read whatever the device writes (should be possible to decode relying on the 'writing docs'), pass the data to the display through the outputs and pass the data to where ever you want too. No need to read the display.

That is essentially my plan. I ordered a LCD to play with, as I don't want to monkey with my working printer. Each button on my printer is attached to a single pin on the atmega, I think running the button board through the rpi gpio will be the easy part. And honestly the serial relay part to a remote device, doesn't seem too scary.