Let's Make Robots!

Serial LCD Controller

Displays stuff sent through a serial connection from a PC or Microcontroller

10 October 2009

I discovered a flaw in the current design that will only allow the controller to work with a connection to the computer and not to a microcontroller.  I've updated the schematic below and will fix the controller design.  I've added a project file below that also includes the fixed schematic. 

If you look at the schematic you will notice that when you set the jumper to non-inverted so you can connect to a microcontroller for serial control it will not work.  The reason is in the way I designed the circuit for both inverted/non-inverted RS232 control.  Looking at the transistor in the circuit, the collector is held high through a 10K resistor.  The collector feeds to the Rx pin on the PIC.  When you set the jumper to non-inverted and attempt to send data to the PIC it won't work because the line is always tied high through R8 to 5V.

There is a fix and I have included it in the archive file below.  There are two ways to do this:

1.  If your board is already built and your intentions are to only use this LCD in a finished design and not attached to the   computer then, snip the connection from R8 to 5V and the controller will only work in the non-inverted configuration.

2. Look at the included schematic in the archive and add the shown J2 jumper to your design which will allow you to select between the two types of communication.

04 October 2009

I have redesigned the LCD Controller and updated the code.  The new schematics and code can be found below.  I ported the code from MBasic to PicBasic Pro.  I'll leave the old code up for those who still want it. 

The files below are from a project that I have been working on for a serial LCD controller for a 4x20 line parallel display with the Hitachi chipset.  I am also working on a USB design.  In the picture of the demo board there is a wire jumper installed.  This is because I screwed the pooch and somehow missed a crossed trace.  I had to repair the board.  In the download files the PCB files have been fixed.  I'll upload some video of functionality when I get a chance.

The code and project files have been posted in the download links.

Project file downloads

Old code:

Power regulation board schematic

LCD and power board PCB

LCD schematic

LCD code

Demo application with sourcecode

05 October 2009 Project Files

PicBasic Pro PIC16F628A code for 16x2 character LCD

PicBasic Pro PIC16F628 code for 16x2 character LCD

PicBasic Pro PIC16F628A code for 20x4 character LCD

Archive containing test application, schematic, and PCB (ExpressPCB)

PicBasic Pro LCD Controller interface to Parallax GPS receiver

Ensure all the files are unzipped to the same folder.  The include file that is referenced contains the fuse settings for the selected PIC chip.

I will be uploading a version soon that allows the type of LCD to be set.  This will allow the same controller to be used for a variety of LCDs.  I can't squeeze that functionality into a PIC16F628 chip without removing some of the current functionality.  So, I am porting that over to a PIC16F88.

More to come...

Breadboard testing of the LCD controller


Software application for testing functionality


LCD controller schematic

A better view of the controller schematic can be downloaded from the link below:

USB version of the LCD controller

seriallcd05.jpgA better view of the controller schematic can be downloaded from the link below:

Optional power supply schematic

power01.jpgA better view of the controller schematic can be downloaded from the link below:


Component layout

PCB with two controllers and the optional power supply


PCB bottom side



PCB top side


LCD prototype board component view


Prototype board attached to the back of a LCD



Serial LCD Controller v1.4


C1    0.1uf   
D1    1N4148   
J1    16-pin Header   
J2    4-pin Header, Right Angle   
J3    3-pin Header   
J4    6-pin Header. Right Angle   
JP1    Shorting Jumper   
Q1    2N2222   
Q2    2N2222   
R1    1M   
R2    10k   
R3    1k   
R4    22k   
R5    15   
R6    10k Potentiometer   
R7    1k   
R8    10k   
U1    PIC16F628   
X1    20Mhz   
HD44780 20x4 LCD Module Display


USB BUS Powered LCD Controller

C1    0.1uF   
C2    10nF   
C3    10uF   
C4    0.1uF   
C5    0.1uf   
D1    1N4148   
F1    500mA, Ferrite Bead   
J1    USB Type B, Digikey 787780-1-ND
J2    ICSP, 6-Pin, Right Angle Header   
J3    LCD Connector, 16-Pin Header   
J5    2-Pin Header   
J6    2-Pin Header   
JP2    Shorting Jumper   
JP3    Shorting Jumper   
LED1    RED   
LED2    GREEN   
Q1    2N2222   
R1    330   
R2    330   
R3    1M   
R4    10k   
R5    15   
R6    1k   
R7    10k   
SW1    Power, SPDT   
U1    FT232RL   
U2    PIC16F628   
X1    20Mhz   

*NOTE* All resistors on the controller board are 1/8 watt


5V Power Regulation v1.0

C1    10uf   
C2    0.1uf   
C3    10uf   
D1    1N4004   
D3    1N4004   
J1    Power Jack       
J2    3-pin header       
LED1    Light Emitting Diode       
R1    220   
SW1    SPDT Slide Switch   
VR1    LM7805

*NOTE* All resistors on the power board are 1/4 watt

You can do a search on eBay for the LCDs and you will find them listed for as cheap as $5.00 minus shipping.

 04 October 2009 - Redesigned Controller

I have redesigned the controller to use some surface mount components.  This is still a prototype and the final version will have all surface mount components and be a bit smaller.  I also ported the code from MBasic to PicBasic Pro.  MBasic is a great program but the makers have not updated it to include newer PICs.  As such, I've been using PicBasic Pro which is a really nice basic compiler.  The code size and speed rivals that of some PIC-C compilers.


Newest Schematic with fix for connection to PC or microcontroller


Better view of the schematic can be downloaded at the following link: http://picasaweb.google.com/lh/photo/0gbrdTCrjH6KJyib-i33EQ?feat=directlink

Old schematic with flaw.  Recommend not to build from this schematic


Better view of the schematic can be downloaded at the following link: http://picasaweb.google.com/lh/photo/Yi30Oi9tf_1AIOc2Z4cDGw?feat=directlink


Better view of the schematic can be downloaded at the following link: http://picasaweb.google.com/lh/photo/ySbtGz3Fb4xDZ26780GD8w?feat=directlinkHobbybotics%20LCD%20Backpack%20v2.4_PCB.jpgHobbybotics%20LCD%20Backpack%20v2.4_PCB.jpg















Hobbybotics LCD Controller V2.3
ComponentDescriptionPart NumberVendorCost
C10.1uf, SMT 080580-C0805C104M5RMouser$0.05
D11N4148, D0-35512-1N4148T26AMouser$0.03
J18-Pin Straight Header, Male855-M20-9730846Mouser$0.20
J26-Pin Receptacle, Female649-68685-306LFMouser$1.75
J36-Pin Receptacle, Female649-68685-306LFMouser$1.75
J46-Pin Polarized Header571-6404546Mouser$0.27
JP12-Pin Jumper855-M22-1920005Mouser$0.25
Q12N2222, SOT-23512-MMBT2222AD87ZMouser$0.06
Q22N2222, SOT-23512-MMBT2222AD87ZMouser$0.06
R11M, 0805, 1/8W71-CRCW0805J-1M-E3Mouser$0.07
R210k, 0805, 1/8W71-CRCW0805-10K-E3Mouser$0.05
R31k, 0805, 1/8W660-RK73B2ATTDD102JMouser$0.06
R422k, 0805, 1/8W71-CRCW0805-22K-E3Mouser$0.05
R515, 0805, 1/8W71-CRCW0805-15-E3Mouser$0.05
R610k, Potentiometer72-T70YE-10KMouser$0.74
R71k, 0805, 1/8W660-RK73B2ATTDD102JMouser$0.06
R810k, 0805, 1/8W71-CRCW0805-10K-E3Mouser$0.05
SW1DIP-2 Switch611-SDA02H1BDMouser$0.56
U1PIC16F628A, SOIC-18579-PIC16F628A-I/SOMouser$2.14
X120Mhz Resonator815-AWCR-20.00MDMouser$0.32
 HD44780 20X4 LCDRT204-1Ebay$10.80
PCBPrinted Circuit BoardHBLCD-V2.2ExpressPCB$14.14



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Now we're getting somewhere.  Let me take another look at the code again.  I probably missed something.

Hi Curtis Brooks!!

     I have an update for you!!

     I just tweaked the code a bit!! I removed the "SAT:" routine from the code that detects the number of satellites!! and now!! I see that the GPS module responds to the commands from the PIC16F84A!! Now!! I'm able to see the data on the LCD!! But!! Not sure how correct I am!!

     The Latitute display is steady and showing up solid!!

     But!! the Longitude gets updated!! and the display does not stay solid!! It keeps refreshing the second line of the LCD at constant intervals!! I'm not sure where to tweak for this in the code!! Please advice!!

     I'm posting a video of my display for your reference!!


     Can you please help me on the code for this!! with the "SAT:" routine present in the code!!

Thanks and Regards,


I'm not able to view your videos.  Can you post them in a different format?

Hi Curtis Brooks!!

     Can you please try to open with VLC player!! Let me know!! Please see the link below!!



 Thanks and Regards,


Hi Curtis Brooks!!

    The Videos are actually .3GP format!! I changed the extension to .AVI!! as .3GP upload was not allowed!! You can change the extension back to .3GP or view the .AVI with winamp!!

 Thanks and Regards,


Okay, I'm looking at video now.  That'll help out with figuring out why the constant updates.  I believe I know what is going on and how to fix it.
I believe I see where the error lies.  The GPS code that is being loaded into the PIC16F84A needs to be modified to be compatible with the command set that our LCD controller expects.  There's some other changes that I would recommend to change also.  I'm throwing a recommended change together to get you going.  I don't have a Parallax GPS receiver but, I do understand the commands from the datasheets.  I'll get something together for you.  Give me a little bit to whip it up.

Hi Curtis Brooks!!

    You're project is amazing!! It works great!! :-)

    As promised!! I've wired your circuit and it works fine for the 16X2 LCD!! But!! there is one thing that I do not understand!!

    The reason I built this is to integrate the Serial LCD with another project which is a GPS Module and a microcontroller!! This is as in the link below!!


    Please see the topic "GPS Receiver"!! I'm using the same GPS module as in the link above!! The code is written in BASIC only!! It can be compiled with PIC Basic PRO 2.47!!

    Please see the code in the above link "http://www.highonsolder.com/storage/code/GPS3.BAS"  (Final GPS PicBasic Code)

    I'm getting the data past the 16F84A microcontroller!! I'm able to see that in my PC's hyperterminal!! But!! the same is not printed in the Serial LCD properly!! The term "Searching for Satellites..." is no getting printed once!! It keeps overwriting on both the lines!! The above link uses a different LCD from Parallax which uses a Basic Stamp as a piggy back board!!

   I'm not really sure as to why this is happening!! Is something in an endless for loop!! Please advice!!

   Can you please help me out on this!! If there is anything to be done on the BASIC code in the above link!! Please advice!!

   I can post a Video if you want !! Let me know!!

 Thanks and Regards,


2X16 Serial LCD

Also, if you are attempting to use that GPS code to output to the LCD controller as written, it will not work as the commands in the PicBasic code are different from what out controller is expecting.  In the zip file above I included a document that explained how to use the commands the controller expects.  I wrote it for a 4-line LCD but, the concept is the same.

Let me knock around with the GPS code you posted and see what I can do to help.  I'll post when working.

Hi Curtis Brooks!!


    There is a PIC16F84A microcontroller inbetween the Parallax GPS Module and the Serial LCD (your design)!!

    The I/O data from the GPS Module is sent to the microcontroller which requests the required data from the module and it receives the data parses and displays it onto the Serial LCD!! This is as in the link "http://www.highonsolder.com/blog/category/gps"

    Please see the schematics in the link http://filer.case.edu/jec24/uploaded_images/GPS-Schematic-759995.jpeg

    You can also get the BASIC code from the link in my previous post!! Please advice!!

Thanks and Regards,