Custom Serial LCD Backpack

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When I first got into BASIC Stamps I was also introduced to the increasingly popular serial LCD since typical microcontrollers would lose too many pins controlling a parallel display. The Scott Edwards displays were the first recommendation and set me back $100.00, which was as much as I paid for the entire microcontroller kit I got to start.


I looked around at other solutions and my then favorite surplus vendor, BG Micro had been selling something called PIC-an-LCD. The concept was that you’d buy this pre-programmed PIC chip and crystal and with a few spare parts, instant serial LCD. They even had a sort of development / evaluation board shown above. This demo board allowed you to connect to a PC or other RS-232 serial port or use TTL compatible serial input. You could control 4 LEDs which demonstrated the extra I/O available from the IC and there was even a piezo speaker to play beeps as commanded by the IC.

The Scott Edwards display had a lot of features, but the PIC-an-LCD had some additional items such as the speaker output and extra I/O. I also realized that there were features missing from both. For example, backlight control would be nice as well as being able to set the initial display message. It’s hard to put a commercially available serial LCD into a design when the display powers up with its own splash screen having nothing to do with your application.


In January of 2002 I was well underway to designing a new Serial LCD Backpack. I knew the market was already flooded but I wanted my own design which would have the features I thought some of the others were lacking or cost too much to get. I used ExpressPCB to create the boards shown above. I fit three on one miniboard layout and cut them apart when I got them.


As you can see from the photo, the boards are just slightly larger than the Scott Edwards backpack even using all through hole parts. It is significantly smaller than the Dale Wheat board, but in all fairness that board was a development board designed for a 4×20 display. For the first batch I decided to use the PIC-an-LCD chip to test the design and layout. Essentially the design is similar to the demo board except that I am using one of the extra I/O lines to control the backlight through a transistor.


Here is a collage photo of the first three prototypes. A 6-pin SIP header interfaces to the outside world. GND, 5V, SIO, and three GPIO lines are available which you can use to drive other devices. Each has a reset button because of being in development and there is a space for the piezo speaker on board, but you can also connect the wires to the pads allowing you to mount the piezo on the front panel with the display. Contrast was handled by the 10K pot on the board.


Future Plans

At the time of this design I had purchased several tubes of SX28 chips to use for the design. Alas, with the EOL on the SX, a different MCU will be used if I ever complete this design. Besides backlight control I was also thinking of implementing backlight brightness using PWM. Software contrast control? Could be a possibility! Custom splash screen and depending on which MCU is used, programmable custom user screens that can be recalled via command.


The original project has been abandoned, however if you have any questions, feel free to comment below and I will share what I have with you. The original modules shown above were given away during The Fellowship Of The Travelling Parts Box endeavor. Please leave a comment below with any questions, suggestions or feedback.


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Electronics Engineer, Hacker and Programmer. Host of Savage///Circuits TV, reviewer of test equipment and Musician.

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