Flip-dot Display

Contents 1 Introduction 2 Modifications 3 Plans 4 Code 4.1 Python 4.2 C

[edit] Introduction

The flip-dot or flip-disc display is a display type invented by Kenyon Taylor designed as a cheap (at the time) public announcement display for applications where the main focus was readability (contrast and size).

Today these signs have been largely replaced by LED-signs or other technologies but during their time of greatness they've been used primarily in public transportation systems (mostly buses) and transport hubs (airports and train and bus stations).

Mobile phone movie about the flip-disc sign

[edit] Modifications

This particular sign was once used to display the destination and transit number of a bus and uses a simple serial protocol over RS485 for communications. The electronics have been modified to accept RS232 due to it's higher availability. The lighting (originally an ordinary white striplight) have been replaced by a blacklight tube to increase the contrast in low-light conditions (the discs are fluorescent yellow).

[edit] Plans

The plan is to make the sign publicly available through our website so that messages can be sent to us on-the-fly.

[edit] Code

[edit] Python

Python client

[edit] C

                                             
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <string.h>
#include <termios.h>
#include <unistd.h>
#include <sys/uio.h>
#define DEFAULT_BAUDRATE B4800
/* ugly but robust and nice for debug */
#define work ((void *)s>=v[i].iov_base&&(void *)s<v[i].iov_base+v[i].iov_len&&i<cnt)
static void xxdv(struct iovec *v,int cnt) {
  char l[80];
  int j,pos;
  unsigned int i=0,addr;
  const unsigned char *s=v[0].iov_base;
  for(addr=0;work;addr+=16) {
    memset(l,' ',sizeof(l));
    for(j=pos=0;j<16&&work;j++,pos+=3) {
      if(8==j)
        l[pos++]=' ';
      snprintf(l+pos,sizeof(l)-pos,"%02x ",*s);
      snprintf(l+50+j,sizeof(l)-50-j,"%c",*s>0x20&&*s<0x7f?*s:'.');
      l[pos+3]=' ';
      if((void *)++s>=v[i].iov_base+v[i].iov_len&&i<cnt)
        s=v[++i].iov_base;
    }
    printf("%06x: %s\n",addr,l);
  }
}
static const speed_t str2br(const char *str) {
  if(!strcmp(str,"115200"))
    return B115200;
  if(!strcmp(str,"57600"))
    return B57600;
  if(!strcmp(str,"38400"))
    return B38400;
  if(!strcmp(str,"19200"))
    return B19200;
  if(!strcmp(str,"9600"))
    return B9600;
  if(!strcmp(str,"4800"))
    return B4800;
  if(!strcmp(str,"2400"))
    return B2400;
  if(!strcmp(str,"1200"))
    return B1200;
  if(!strcmp(str,"600"))
    return B600;
  if(!strcmp(str,"300"))
    return B300;
  return DEFAULT_BAUDRATE;
}
static const int br2i(const speed_t br) {
  if(B115200==br)
    return 115200;
  if(B57600==br)
    return 57600;
  if(B38400==br)
    return 38400;
  if(B19200==br)
    return 19200;
  if(B9600==br)
    return 9600;
  if(B4800==br)
    return 4800;
  if(B2400==br)
    return 2400;
  if(B1200==br)
    return 1200;
  if(B600==br)
    return 600;
  if(B300==br)
    return 300;
  return -1;
}
unsigned char cksum(unsigned char start,const unsigned char *s, int len) {
  unsigned char c=start;
  int i;
  for(i=0;i<len;i++)
    c+=s[i];
  return c;
}
static inline iov_set(struct iovec *v,int i,void *base,size_t len) {
  v[i].iov_base=base;
  v[i].iov_len=len;
}
int main(int argc,char *argv[]) {
  int i,fd,slen;
  char *s;
  unsigned char c;
  struct iovec iov[5];
  speed_t br=DEFAULT_BAUDRATE;
  struct termios tios;
  if(argc<3) {
    printf("syntax: %s tty [baudrate (default=%d)] text\n", *argv, br2i(br));
    return 1;
  }
  if(-1==(fd=open(argv[1],O_RDWR))) {
    perror("open");
    return 1;
  }
  if(argc>3)
    br=str2br(argv[2]);
  if(-1==tcgetattr(fd,&tios)) {
    perror("tcgetattr");
    return 1;
  }
  cfmakeraw(&tios);
  printf("setting baudrate %d\n",br2i(br));
  if(-1==cfsetspeed(&tios,br)) {
    perror("cfsetspeed");
    return 1;
  }
  if(-1==tcsetattr(fd,TCSANOW,&tios)) {
    perror("tcgetattr");
    return 1;
  }
  i=0;
  iov_set(iov,i++,"\xff",1);
  iov_set(iov,i++,"\x06\xa2",2);
  s=argv[argc>3?3:2];
  slen=strlen(s);
  iov_set(iov,i++,s,slen);
  c=cksum(6+162,s,slen);
  iov_set(iov,i++,&c,1);
  iov_set(iov,i++,"\xff",1);
  printf("writing %d bytes\n",5+slen);
  xxdv(iov,i);
  if(-1==(i=writev(fd,iov,i)))
    perror("writev");
  else
    printf("%d bytes written\n",i);
  close(fd);
  return i!=5+slen;
}