Very Low power 3 digit LCD Display with serial control

I had a need for a LCD display that consumed very little power and generated very little digital noise . You can buy LCD’s with driver chips but I have had great difficulty with these modules because they create excessive wide band noise.

To solve this problem, I made an LCD driver out of a 18F26K22 PIC micro-controller and a low cost static LCD display module. A static module requires more pins( a pin for every segment) but the drive logic is easier to implement. You cannot simply drive the the LCD segment high or low, as with a seven segment LED display. Once the capacitance of the display charges up, the segment contrast fades. The solution is to cycle a given segment on and off  at rate fast enough not to strobe(100Hz in my case).

In my design, the  display is driven by a four byte serial data packet which consists of: <startbyte>,<digit1>,<digit2>,<digit3> . The data bytes are sent as rs232 data at 9600 baud.

The startbyte is one of  three values(shown here in HEX): oxA0(no decimal point), 0xA1(decimal point 1st digit), 0xA2(decimal point 2nd digit). The valid data bytes are 0-9(non ASCII) and ASCII characters, “A”, “C”, “E”,”F”, “H”, and “P”. If you send any other values for a given digit, it will clear(blank the digit)

The module is clocked using the internal RC clock at 1Mhz and only draws 500uA when operating. It must be operated at greater than 4v or the LCD will be faint. If using a 3v supply, you can use a simple Dickson voltage doubler circuit to generate the supply voltage.

Picture of module(LCD covers the micro-controller):


Demo Video: (Radio Receiver using the display module)

Schematic Diagram:


Link:   Zip File with ExpressPCB layout file and HEX file


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