Planet Arduino

In this article we examine another style of vintage display technology – the incandescent seven-segment digital display. We are using the FFD51 by the IEE company (data sheet.pdf) – dating back to the early 1970s. Here is a close-up of our example:

You can see the filaments for each of the segments, as well as the small coiled ‘decimal point’ filament at the top-right of the image above.  This model has pins in a typical DIP format, making use in a solderless breadboard or integration into a PCB very simple:

It operates in a similar manner to a normal light bulb – the filaments are in a vacuum, and when a current is applied the filament glows nicely. The benefit of using such as display is their brightness – they could be read in direct sunlight, as well as looking good inside.  At five volts each segment draws around 30mA. For demonstration purposes I have been running them at a lower voltage (3.5~4V), as they are old and I don’t want to accidentally burn out any of the elements.

Using these with an Arduino is very easy as they segments can be driven from a 74HC595 shift register using logic from Arduino digital out pins. (If you are unfamiliar with doing so, please read chapters four and five of my tutorial series). For my first round of experimenting, a solderless breadboard was used, along with the usual Freetronics board and some shift register modules:

Although the modules are larger than a DIP 74HC595, I like to use these instead. Once you solder in the header pins they are easier to insert and remove from breadboards, have the pinouts labelled clearly, are almost impossible to physically damage, have a 100nF capacitor for smoothing and a nice blue LED indicating power is applied.

Moving forward – using four shift register modules and displays, a simple four-digit circuit can be created. Note from the datasheet that all the common pins need to be connected together to GND. Otherwise you can just connect the outputs from the shift register (Q0~Q7) directly to the display’s a~dp pins.

Some of you may be thinking “Oh at 30mA a pin, you’re exceeding the limits of the 74HC595!”… well yes, we are. However after several hours they still worked fine and without any heat build-up. However if you displayed all eight segments continuously there may be some issues. So take care. As mentioned earlier we ran the displays at a lower voltage (3.5~4V) and they still displayed nicely. Furthermore at the lower voltage the entire circuit including the Arduino-compatible board used less than 730mA with all segments on –  for example:

 For the non-believers, here is the circuit in action:

Here is the Arduino sketch for the demonstration above:

Now for the prototype of something more useful – another clock. Time to once again pull out my Arduino-compatible board with onboard DS1307 real-time clock. For more information on the RTC IC and getting time data with an Arduino please visit chapter twenty of my tutorials. For this example we will use the first two digits for the hours, and the last two digits for minutes. The display will then rotate to showing the numerical day and month of the year – then repeat.

Operation is simple – just get the time from the DS1307, then place the four digits in an array. The elements of the array are then sent in reverse order to the shift registers. The procedure is repeated for the date. Anyhow, here is the sketch:

#include "Wire.h"
#define DS1307_I2C_ADDRESS 0x68
// note the digital pins of the arduino that are connected to the nixie driver
int clockPin = 7;
int latchPin = 8;
int dataPin = 9;
int clockArray[5]; // holds the digits to display
int a=0;
// the bits represent segments a~dp from left to right
// if you add one to the number (or turn on the last bit) the decimal point turns on
byte numbers[]={
 B11111100, // digit zero
 B01100000,
 B11011010,
 B11110010,
 B01100110,
 B10110110,
 B10111110,
 B11100000,
 B11111110,
 B11110110}; // digit nine
// Convert normal decimal numbers to binary coded decimal
byte decToBcd(byte val)
{
 return ( (val/10*16) + (val%10) );
}
// Convert binary coded decimal to normal decimal numbers
byte bcdToDec(byte val)
{
 return ( (val/16*10) + (val%16) );
}
void setDateDs1307(byte second, // 0-59
byte minute, // 0-59
byte hour, // 1-23
byte dayOfWeek, // 1-7
byte dayOfMonth, // 1-28/29/30/31
byte month, // 1-12
byte year) // 0-99
{
 Wire.beginTransmission(DS1307_I2C_ADDRESS);
 Wire.send(0);
 Wire.send(decToBcd(second)); // 0 to bit 7 starts the clock
 Wire.send(decToBcd(minute));
 Wire.send(decToBcd(hour)); 
 Wire.send(decToBcd(dayOfWeek));
 Wire.send(decToBcd(dayOfMonth));
 Wire.send(decToBcd(month));
 Wire.send(decToBcd(year));
 Wire.send(0x10); // sends 0x10 (hex) 00010000 (binary) to control register - turns on square wave
 Wire.endTransmission();
}
// Gets the date and time from the ds1307
void getDateDs1307(byte *second,
byte *minute,
byte *hour,
byte *dayOfWeek,
byte *dayOfMonth,
byte *month,
byte *year)
{
 // Reset the register pointer
 Wire.beginTransmission(DS1307_I2C_ADDRESS);
 Wire.send(0);
 Wire.endTransmission();
 Wire.requestFrom(DS1307_I2C_ADDRESS, 7);
 // A few of these need masks because certain bits are control bits
 *second = bcdToDec(Wire.receive() & 0x7f);
 *minute = bcdToDec(Wire.receive());
 *hour = bcdToDec(Wire.receive() & 0x3f); // Need to change this if 12 hour am/pm
 *dayOfWeek = bcdToDec(Wire.receive());
 *dayOfMonth = bcdToDec(Wire.receive());
 *month = bcdToDec(Wire.receive());
 *year = bcdToDec(Wire.receive());
}
void setup()
{
 byte second, minute, hour, dayOfWeek, dayOfMonth, month, year;
 pinMode(latchPin, OUTPUT);
 pinMode(clockPin, OUTPUT);
 pinMode(dataPin, OUTPUT);
 Wire.begin();
// Change these values to what you want to set your clock to.
 // You probably only want to set your clock once and then remove
 // the setDateDs1307 call.
second = 00;
 minute = 35;
 hour = 17;
 dayOfWeek = 5;
 dayOfMonth = 29;
 month = 4;
 year = 12;
 // setDateDs1307(second, minute, hour, dayOfWeek, dayOfMonth, month, year);
}
void showTime()
{
 byte second, minute, hour, dayOfWeek, dayOfMonth, month, year;
 getDateDs1307(&second, &minute, &hour, &dayOfWeek, &dayOfMonth, &month, &year);

 if (hour<10)
 {
 clockArray[1]=0;
 clockArray[2]=hour;
 }
 if (hour>9)
 {
 clockArray[1]=int(hour/10);
 clockArray[2]=hour%10;
 } 
 if (minute<10)
 {
 clockArray[3]=0;
 clockArray[4]=minute;
 }
 if (minute>9)
 {
 clockArray[3]=int(minute/10);
 clockArray[4]=minute%10;
 }
 displayArray();
}
void showDate()
{
 byte second, minute, hour, dayOfWeek, dayOfMonth, month, year;
 getDateDs1307(&second, &minute, &hour, &dayOfWeek, &dayOfMonth, &month, &year);

 if (dayOfMonth<10)
 {
 clockArray[1]=0;
 clockArray[2]=dayOfMonth;
 }
 if (dayOfMonth>10)
 {
 clockArray[1]=int(dayOfMonth/10);
 clockArray[2]=dayOfMonth%10;
 }
 if (month<10)
 {
 clockArray[3]=0;
 clockArray[4]=month;
 }
 if (month>10)
 {
 clockArray[3]=int(month/10);
 clockArray[4]=month%10;
 }
 displayArray();
}
void displayArray()
// sends the data from clockArray[] to the shift registers
{
 digitalWrite(latchPin, LOW);
 shiftOut(dataPin, clockPin, LSBFIRST, numbers[clockArray[4]]); // digit 4 
 shiftOut(dataPin, clockPin, LSBFIRST, numbers[clockArray[3]]); // digit 3 
 shiftOut(dataPin, clockPin, LSBFIRST, numbers[clockArray[2]]+1); // digit 2 and decimal point
 shiftOut(dataPin, clockPin, LSBFIRST, numbers[clockArray[1]]); // digit 1
 digitalWrite(latchPin, HIGH);
}
void loop()
{
 showTime(); // display the time 
 delay(5000);
 showDate(); // display the date (day and month) for two seconds
 delay(2000);
}

and the clock in action:

So there you have it – another older style of technology dragged into the 21st century. If you enjoyed this article you may also like to read about vintage HP LED displays. Once again, I hope you found this article of interest. Thanks to the Vintage Technology Association website for background information.

The post Arduino and FFD51 Incandescent Displays appeared first on tronixstuff.