LED Filament clock

wpe90.jpg (40899 bytes)

A clock using "LED filament" strips

wpe93.jpg (22280 bytes) wpe92.jpg (4944 bytes)

Please watch the video first - I don't have time to write it all out!

Notes

"LK" parts are 1206 zero-ohm links, not shown on schematic.
32K SMD crystal is an Abracon ABS25. You can also use a metal-can type. Note these come in various accuracy specs - get the best one you can.
RS1D is a 200V 1A fast diode. Anything similar should be fine.
No I can't give you detailed BOM for Digikey etc. Everything you need is on the schematic.
Search Ebay or Aliexpress for "LED Filament" to find the LED filament strips.
Current draw at 12V is approx 150mA with LED voltage set to 75V (depends on LED voltage setting). (If it draws more than about 250mA, it may go into thermal runaway so reduce LED voltage)
Reed switches are used for time setting to avoid need for external switches. PCB will accept a variety of reed or pushbutton switches
Inductor choice is rather critical. Bourns SRR5028 was found to perform best for this size. If using something else, test it with all segments on and monitor power draw - if you see it start to increase, bad things may happen.
Check for shorts between the 75V rail and anything else before first powering on to avoid smoke issues.

No I'm not interested in making one for you or selling PCBs or supplying preprogrammed PICs, sorry.

For discussion, please use this EEVBLOG thread.

Things that can be improved

Increase digit spacing.
Tinted front window materials/diffuser to improve contrast between on & off segments
High voltage PSU is only just good enough for the job - it runs quite warm, and above about 80V may go into thermal runaway if lots of digits are on. Should probably be replaced with something more efficient, plus a seperate 5V regulator.
It should be fairly easy to add backup from battery or supercap - isolate PIC supply with a diode, and add code to sense power fail (Use a spare input pin to sense non backed-up 5V rail) and go to sleep mode, after setting all outputs low to avoid leaking power to drivers. Periodically wake on timer 1 interrupt up to maintain time and check if power has come back.
Light sensing for auto brightness control (using PWM on driver output enable) - the display will be way too bright to use in a bedroom
Smooth digit fade up/down to look more like a real filament.
Calibration for fine-tuning accuracy.

Schematic. PDF Version

wpe8C.jpg (84645 bytes)

PCB layout - rear view

PDF - colour
PDF - monochrome, mirrored for printing on transparency to home etching
PCAD2006 PCB file NO! I CAN'T SEND YOU A FILE FOR ***ING EAGLE, KICAD or any other PCB software OK! (But I think you can import PCAD into Altium)
Gerber and drill files

wpe8F.jpg (241761 bytes)

wpe91.jpg (87095 bytes)

Detail of sockets

wpe94.jpg (8539 bytes)

PIC Code (for Microchip XC8)

#include <pic.h>

// filament clock
// (c) Mike Harrison 2015
// www.electricstuff.co.uk

// Target PIC16F1824

#pragma config FOSC=INTOSC,MCLRE=ON,WDTE=ON,PWRTE=ON,BOREN=ON,CLKOUTEN=OFF
#pragma config LVP=OFF,BORV=HI,WRT=OFF

#define oe LATA2 // tpic595 latch output enable. Could use PWM for global dimming, or multi-cycle pulses for per-segment dimming
#define lat LATC1 // tpic595 latch

// set switches
#define minsw RA0
#define hrsw RA1

// segment bits within shift registers
#define sa 4
#define sb 8
#define sc 16
#define sd 32
#define se 64
#define sf 2
#define sg 128
#define sx 1 // 10Hrs, colon

// seven-segment lookup

const char sevenseg[10]={
sa | sb | sc | sd | se | sf,
sb | sc,
sa | sb | sd | se | sg,
sa | sb | sc | sd | sg,
sb | sc | sf | sg,
sa | sc | sd | sf | sg,
sa | sc | sd | se | sf | sg,
sa | sb | sc ,
sa | sb | sc | sd | se | sf | sg,
sa | sb | sc | sd | sf | sg
};

unsigned char hsecs,mins,hours,colon; // NB hsecs counts half-seconds

void spibyte(char c)
{ // send byte to SPI port
SSP1IF=0;
SSP1BUF=c;
while(~SSP1IF);
}

void main(void)
{

    OSCCON=0b01110000; // 8MHz
    LATA=0;
    TRISA=0b00110011;
    WPUA =0b00000011; // pullups for switches
    ANSELA=0;

    LATC=0;
    TRISC=0b00000000;
    WPUC =0b00000000;
    ANSELC=0;
    OPTION_REG=0b00000000;
    APFCON0=0; APFCON1=0;
    // SPI setup
    SSP1STAT=0b01000000; // CKE high
    SSP1CON1=0b00100000; // master mode, clk=fosc/4
    SSP1CON2=SSP1CON3=0;

    T1CON=0b10001001; // timer1 on, T1 oscillator

oe=0; // output enable

hours=0; // "power out" indication, prevent counting
mins=0;
hsecs=0;
TMR1IF=1; // force initial update - 32K osc can take a few secs to start

do {

asm("clrwdt");

if (hours==0) if((minsw==0) || (hrsw==0)) hours=1; // start running after powerdown

if(TMR1IF) { // 2Hz tick
TMR1IF=0;
TMR1H|=0xC0; // preload Tmr1 for 2Hz=16384 counts

colon=hsecs&1;

if(minsw==0) if(++mins==60) mins=0;
if(hrsw==0) if(++hours==13) hours=1;

if(hours) // not startup
if(++hsecs==120) {
hsecs=0;
if(++mins==60) {
mins=0;
if(++hours==13) {
hours=1;
}
    }
}

lat=0;
spibyte(sevenseg[hours%10] | (hours>9?sx:0));
spibyte(sevenseg[mins/10] | (colon?sx:0));
spibyte(sevenseg[mins%10]);
lat=1;

}

} while(1);


    }

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