Bus Pirate v3 LCD adapter hardware design
From DP
Control HD44780 LCDs from the Bus Pirate v3 with this breakout board. The Bus Pirate LCD mode uses an adapter because there aren't enough pins to directly control a character display.
You can build the adapter with a few parts and a bread board, or you can buy it ready-made at Seeed Studio for $9.00. Includes a short connector cable. Every sale directly supports open source development of the Bus Pirate.
You can get a Bus Pirate LCD adapter v3 for $9.
Read about the design below.
Contents |
Overview
Since the Bus Pirate v3 doesn't have enough pins to drive the HD44780 directly, we had to add a serial shift register to drive it. The board also features hardware contrast, and brightness adjustment, as well as software backlight control.
Hardware
Click for a full size schematic image. Schematic and PCB were designed with the freeware version of Cadsoft Eagle, download the latest project files from our Google Code project page.
74HCT595 serial shift register
To successfully control the LCD, more pins need to be added to the Bus Pirate. We tackled this problem by adding the '595 8bit serial shift registrar (IC1), which is decoupled with a 0.1uF capacitor (C1). It also drives an LED (LED1) through a 1K resistor (R1).
The LCD is controlled in 4bit mode, using 4 pins of the 74HCT595's output for the D7-D4 LCD pins. Another 3 pins are used for LCD's control signals. The LED (LED1) is driven by the 8th pin of the '595.
Contrast
Here is a 10K trimmer which creates a voltage divider for contrast pin of the LCD. Turn it to adjust the contrast.
Brightness
LCD's have all sorts of different backlights. We included a bunch of jumpers to accommodate many different types. Make sure yours uses a simple voltage before connecting any of the jumpers.
Pin 15 is generally the anode of a common LCD backlight. It's connected through a 100 Ohm trimmer labeled 'Brightness' on the board. Some LCD's require a resistor on the backlight LED, some don't, check your datasheet to be sure. If it does need it, we've included the trimmer on board. Connect the 'ANODE' jumper if you are sure your backlight requires a 5v supply. It will provide 5V to LCD pin 15 through the 'Backlight' trimmer.
The common backlight cathode (pin 16) of the LCD is connected to a 2-way jumper 'Cathode'. It can be connected directly to ground, or to the collector of transistor 'T1'. The transistors base is connected to the 'AUX' pin of the Bus Pirate giving you the ability to control the backlight through the Bus Pirate's PWM command.
Some LCD's feature opposite connections, where the backlight anode is connected to pin 16, and the cathode is connected to pin 15. In this case you'll need to uses jumper wires crisscrossing between the two jumper footprints.
HD44780 header
The breakout includes the most common 16pin header for HD44780 compatible LCDs.
A future version will also have an optional 2x8 header footprint, supporting those HD44780 compatible LCDs that use it..
Bus Pirate v3 IO header
The Bus Pirate controls the 74HCT595 serial to parallel chip over the SPI, using a hardware SPI module. The IO header on the LCD adapter connects directly to the Bus Pirate header to carry the SPI signals, as well as the pulse width modulator to control the backlight, and power for the LCD.
PCB
We used the freeware version of Cadsoft Eagle to make the schematic and PCB. Download the latest designs and firmware from the project Google Code page.
Partslist
Click for a full size placement image.
| Part | Quantity | Value | Package |
|---|---|---|---|
| ANODE | 1 | Jumper | 1X02 |
| C1 | 1 | 0.1uF | C0805 |
| IC1 | 1 | 74HCT595D | SO16 |
| CATHODE | 1 | 2-way Jumper | 1X3 |
| JP1 | 1 | Shrouded 2x5 header | Shrouded 2x5 |
| LCD | 1 | Female 1x16 header | 1X16 |
| LED1 | 1 | LED | 0805 LED |
| Contrast | 1 | 10K Trimmer | CA6V |
| R2,R4 | 2 | 1K | M0805 |
| Brightness | 1 | 100R | CA6V |
| T1 | 1 | NPN Transistor | SOT23-BEC |
Find parts using the master partlist.
Get one!
You can get one for $9.00 at Seeed.
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