Thursday, May 17, 2012

LCD serial display out of an old Palm

Here's a good way of recycling old hardware: Use a palm device for your Arduino projects as a full-featured display.

You may want to get rid of the DB9 serial cable by just cutting it from the cradle and adding this small and cheap TTL-RS232 converter made of two transistors and four resistors. This circuit is a must, since the palm device uses RS232 levels to communicate while your Arduino or other micro will most likely use TTL levels.

Make sure you have some spare method to transfer software from the computer to the palm if needed, such as an SD card.

The circuit in place.

Rear view of the cradle.

The circuit fits nicely in the cradle, and the schematics are a modified design taken from Jim's Projects [Link] I made a different design choice here, and pull up the palm's RX line directly from +5V instead of doing it from DTR.

Schematics for the TTL-RS232 conversion circuit.

If you don't plan to use your Palm as a serial input device, then the TX line of the Palm (pin 2) is optional and you may wish to use only the output line of your microcontroller for a unidirectional configuration.

The finished setup at work. You can keep it handy in your workbench. The stand helps to keep it at a nice view angle.

Here you can see a repurposed Palm with PalmOrb software, which emulates a 16x4 LCD screen.
However you can use any standard Palm terminal software.

Plug and Play, no especial libraries required in the Arduino.