It would be a useful interface to be able to use a Sparkfun 16×2 serial LCD display (LCD-09395 for the Black and White version) to show what is being sent on the console for the Raspberry Pi. The utility could range from managing a headless RPi to being a stand alone output display. There are several steps in the project.
Pin, Function (RPi GPIO Connector)
- 1, 3.3 VDC… connects to input of level shifter
- 2, 5.0 VDC… connects to VDD of Sparkfun
- 6, Ground… Connects to Ground of Sparkfun
- 8, TDx… Connects to input on level shifter
Hardware: The signal levels from RPi are 0 – 3.3 VDC, while the serial interface for the Sparkfun LCD ranges from the typical TTL levels of 0 – 5.0 VDC. Although it does not appear that a level converter is absolutely required, it is always a good idea to not press the margins as it decreases troubleshooting time if relatively simple to implement. In this case it is using a 2N7000 N Channel MOSFET as a level shifer.
As per suggestions from Sparkfun and others, we have used on 2N7000 as a level shifter from the 3.3 VDC coming out of the Tx to the 5.0 expected by the Sparkfun in its input connection.
SK Pang Electronics has a basic setup for serial communications described:
And another good reference is:
However, trying various commands I can’t seem to get the Tx pin to wiggle – either have the scope move or see a change in the characters on the LCD display. So at this time, I am going to stop any more investigation into this side path and look at alternative paths forward. For the record, the LCD works, startup screen turns on, and RPi works. They just are not talking.
Focus on temp. logging VS. LCD Console, VS. Audio projects. A wide range… but one where I can task switch and look at something new.
Time for a change to audio! I have just assembled 31″ stands and will put in the 4″ foam wedges behind and aside the speakers (M&K) to optimize the sound quality coming out of them. I would like to optimize room acoustics and then possible spend some money on speakers/CD player and who knows!