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G Giles

Member Since 17 Aug 2010
Offline Last Active Oct 24 2010 10:50 PM

Topics I've Started

Seven Segment Display with the MC14489 Chip

26 September 2010 - 09:46 PM

This project uses a MC14489 Multicharacter LED Display/Lamp Driver. One chip can control a 5 digit display plus decimals. Many alphanumeric characters can be displayed as well. It uses one resistor to control LED current. This resistor could be a light sensitive resistor to compensate for light levels. The interface is serial; compatible with SPI. With one chip, several shift registers can be replaced. The chip can be cascaded to give long displays.

I had an old, defective CO detector with a 3 digit LED display. When I dismantled it, I noticed that the display was driven by an MC14489 chip and a Motorola microcontroller. Using a meter, the Enable, Data and Clock pins were determined. The specifications for the MC14489 chip are online in several places- http://www.rasmicro....mc14489rev4.pdf .

The chip uses two registers to control and display the characters. One is an 8 bit Control register that allows the user to specify whether the characters displayed are HEX numerals or specially decoded alphanumerics. The second register is 24 bits (3 bytes), containing nybbles that specify the characters displayed. Bit 23 to bit 20 (MSB’s) control the decimal points and display brightness. The bits are clocked into the chip MSB first. The controller automatically steers the bits to the proper register, detecting 8 bits or 24 bits. The data in the registers are latched on the low to high transition of the enable line.

Code from http://geekswithblog...nking_leds.aspx is used and modified (simplified, I am much more familiar with VB.Net) to run the MC14489 display. It uses one of the ADC ports to measure the voltage on a voltage divider consisting of a resistor and a cadmium sulphide light dependant resistor to measure ambient light levels.
The ADC data is read 100 times and averaged. The display digit character code is read from a table and ‘OR’ed into the appropriate nybble. A more sophisticated way of displaying characters would involve parsing the HEX and alphanumeric characters from the table and modifying the control register to display the correct character. This could include the ability to display blanks, degrees for temperature and a leading negative sign. has the code for this kind of parsing.

notEnable is connected to Pin D8
Clock is connected to Pin D12
Data is connected to Pin D11

using System;
using System.Threading;
using Microsoft.SPOT.Hardware;
using SecretLabs.NETMF.Hardware;
using SecretLabs.NETMF.Hardware.Netduino;

namespace MC14489_Driver
    class DisplaywithAnalogInput : IDisposable

        private readonly short numDisplayReg = 3;   // MC14489_Driver display registers 
        private readonly byte ConfigValue = 0x01;   // hexadecimal code on all
        private readonly byte DecReg = 0xA0;        // decimal and brightness code

        OutputPort notEnable = new OutputPort(Pins.GPIO_PIN_D8, false);
        OutputPort clockPort= new OutputPort(Pins.GPIO_PIN_D12, false);
        OutputPort dataPort=new OutputPort(Pins.GPIO_PIN_D11, false);

        // Initialize analog input for potentiometer
        AnalogInput analogPort = new AnalogInput(Pins.GPIO_PIN_A0);

        public DisplaywithAnalogInput()

            // Set value range to display in 3 digits
            analogPort.SetRange(0, 999);

            // Init the MC14489_Driver Control Register 

        public void Run()
            while (true)
                // Read analog value 
                var value = analogPort.Read();

                // read 99 more readings
                for (int i = 1; i < 100; i++)
                    value = value + analogPort.Read(); 
                // calculate average
                value = value / 100;

                // Show the value


                // Wait a little

        public void Write(params byte[] buffer)
            if (buffer == null) throw new ArgumentNullException("buffer");
            if (buffer.Length > numDisplayReg) throw new ArgumentOutOfRangeException("buffer too large");

            // Ground notEnable and hold low for as long as you are transmitting the register bytes

            for (int i = buffer.Length-1; i >= 0; i--)

            // Pulse the notEnable pin high to signal chip to diplay the data

        private void ShiftOut(byte value)
            // Lower Clock

            byte mask;
            for (int i = 0; i < 8; i++)
                mask = (byte)(1 << (7 - i));

                dataPort.Write((value & mask) != 0);

                // Raise Clock

                // Lower Clock


        public void ShowValue(int value)
            int ptr;
            // Map digits to output patterns
            var buffer = new byte[numDisplayReg];
            buffer[0] = 0x00;
            buffer[1] = 0x00;
            buffer[2] = DecReg;

            for (int i = 1; i < numDisplayReg * 2 ; i++)
               byte digit = digits[value % 10];
               if ((i % 2) == 0) //upper nybble - shift 4 bits left
                   digit = (byte)(digit * 16);     
               ptr = (i - 1) / 2;
               buffer[ptr] = (byte)(digit | buffer[ptr]);

                value = value / 10; // next digit

            // Write output buffer

        public void SetConfig(byte ConfigSet)
            // Map digits to output patterns
            var buffer = new byte[1];
            buffer[0] = ConfigSet;
            // Write output buffer

        public void Dispose()
        private static readonly byte[] digits = new byte[]
                                                        0x00, // B00000000 = 0
                                                        0x01, // B00000001 = 1 
                                                        0x02, // B00000010 = 2
                                                        0x03, // B00000011 = 3
                                                        0x04, // B00000100 = 4
                                                        0x05, // B00000101 = 5
                                                        0x06, // B00000110 = 6
                                                        0x07, // B00000111 = 7
                                                        0x08, // B00001000 = 8
                                                        0x09  // B00001001 = 9 

Problem with Analog Input

23 September 2010 - 02:28 PM

Hi, I am trying to use the code for Seven Segment display using the analog input. The port seems to set up fine and the 'SetRange' seems to execute. When the 'var value = analogPort.Read();' statement executes, the program stops and requests the user find the file 'ANALOGINPUT.CS' Why would this be happening? Thanks, Greg analogPort = new AnalogInput(Analog_Pin); // Set value range to display in 2 digits analogPort.SetRange(0, 99); } public void Run() { while (true) { // Read analog value var value = analogPort.Read();

USB to PC and Program connection

17 August 2010 - 09:21 PM

Hi, I am thinking down the road as far as projects are concerned, but I was wondering if the Netduino can be programmed to transfer data to and from the Netduino running in a standalone mode to a PC. For Example, a button is pressed on the Netduino or an analog value is registered and it sends useable results to a program running on a PC - outside of the framework. Seems to be an impressive little piece of hardware! Thanks, Greg

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