For this project, I wanted to build a device capable of displaying up
to 8 digits on a seven segment display. Sounds easy, right? The catch
is, I wanted to retrieve these digits from the Internet over WiFi.
I took this opportunity to try out the ever-popular Arduino platform. Arduino turned out to be a good choice for this project for several because it has:
- an easy to use, Arduino compatible WiFi adapter (WiShield) put out by asynclabs
- a library available for talking to the WiShield with examples included
- a MAX7219 interface library
- an onboard USB programmer and a software programmer that works on Ubuntu
This is the first electronics project I’ve attempted from scratch so I’m quite pleased with the result. In fact, I’m looking for larger 7 segment digits to build a much larger display.
I began this project by purchasing a MAX7219 display driver, an Arduino Uno, 8 seven segment common cathode LED digits, a breadboard, some jumper wires and A/B USB cable. It took me a few hours to properly connect the displays to the display driver, but seeing the test routine properly on the digits was satisfying enough to make it worth the effort. One problem I ran into was in selecting the proper resistor for Rset which sets the display brightness. After reading the datasheet, I selected a 10kΩ resistor which turned out to be wrong because the display would quickly flicker off after a brief moment. Adding a second resistor in series seemed to fix the problem.
Bolstered by my success in displaying hard-coded numbers, I ordered the WiShield. It arrived a few weeks later and I dropped it right in. Getting a simple WiFi enabled program running is as simple as cloning asynclab’s WiShield git repository, making a few modifications, and uploading one of the example scripts. At this point, I had all the hardware I needed to make this device get information from the Internet and display it. The final missing piece was the software. This part took the longest, mostly because I have almost no experience writing in C. I had the whole thing working with DHCP and DNS resolution, but it was unstable for some reason. I ended up with the following attrocity:
#include <WiShield.h>
#include <LedControl.h>
extern "C" {
#include "uip.h"
}
#define ISO_nl 0x0a
#define ISO_cr 0x0d
// Wireless configuration parameters ----------------------------------------
unsigned char local_ip[] = {10,10,0,91}; // IP address of WiShield
unsigned char gateway_ip[] = {10,10,0,3}; // router or gateway IP address
unsigned char subnet_mask[] = {255,255,255,0}; // subnet mask for the local network
char ssid[] = {"SOMESSID"}; // max 32 bytes
unsigned char security_type = 3; // 0 - open; 1 - WEP; 2 - WPA; 3 - WPA2
unsigned char wireless_mode = 1; // 1==Infrastructure, 2==Ad-hoc
unsigned char ssid_len;
unsigned char security_passphrase_len;
int closedLoop = 0;
// WPA/WPA2 passphrase
const prog_char security_passphrase[] PROGMEM = {"somewpapassphrase"}; // max 64 characters
// WEP 128-bit keys
prog_uchar wep_keys[] PROGMEM = {
0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, // Key 0
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // Key 1
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // Key 2
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 // Key 3
};
// End of wireless configuration parameters ----------------------------------------
// global data
boolean connectAndSendTCP = true;
uip_ipaddr_t srvaddr;
LedControl lc=LedControl(5,6,7,1);
void setup()
{
// Enable Serial output
Serial.begin(57600);
lc.shutdown(0,false);
lc.setIntensity(0,9);
initialize();
}
void initialize()
{
Serial.println("Establishing WifFi Connection");
WiFi.init();
uip_sethostaddr(local_ip);
uip_setdraddr(gateway_ip);
uip_setnetmask(subnet_mask);
delay(100);
}
unsigned long entryTimer = 12000;
void loop()
{
if (entryTimer > 0 && entryTimer % 100 == 0) {
Serial.println(entryTimer);
}
if (true == connectAndSendTCP) {
entryTimer++;
if ((entryTimer > 12000) && (true == connectAndSendTCP)) {
connectAndSendTCP = false;
entryTimer = 0;
Serial.println("inside");
// Address of server to connect to
uip_ipaddr(&srvaddr, 173,203,98,126);
uip_conn = uip_connect(&srvaddr, HTONS(80));
if (NULL == uip_conn) {
Serial.println("could not connect");
}
}
}
delay(10);
WiFi.run();
}
void (*softReset) (void) = 0; //declare reset function @ address 0
extern "C" {
void printx(char *stuff)
{
Serial.println(stuff);
}
// Process UDP UIP_APPCALL events
void udpapp_appcall(void)
{
uip_dhcp_run();
}
// DHCP query complete callback
void uip_dhcp_callback(const struct dhcp_state *s)
{
}
char requestLine[] = "GET /some/path.txt HTTP/1.1\r\nUser-Agent: uIP/1.0\r\nHost: example.com\r\nConnection: Close\r\n\r\n";
void socket_app_appcall(void)
{
struct socket_app_state *s = &(uip_conn->appstate);
if(uip_closed() || uip_timedout()) {
Serial.print("Closed loop: ");
Serial.println(closedLoop);
if (closedLoop > 2) {
//initialize();
softReset();
}
closedLoop++;
Serial.println("SA: closed / timedout");
connectAndSendTCP = true;
}
if(uip_poll()) {
}
if(uip_aborted()) {
connectAndSendTCP = true;
Serial.println("SA: aborted");
}
if(uip_connected()) {
Serial.println("Sending:");
Serial.println(requestLine);
uip_send(requestLine, strlen(requestLine));
closedLoop = 0;
}
if(uip_acked()) {
Serial.println("SA: acked");
}
if(uip_newdata()) {
Serial.println("SA: newdata");
int len = uip_datalen();
int pos = -1;
int linenumber = -1;
int linepos = 0;
boolean startresponsedata = false;
boolean newline = false;
char emptyline[8] = {0, 0, 0, 0, 0, 0, 0, 0};
char linezero[8] = {0, 0, 0, 0, 0, 0, 0, 0};
char lineone[8] = {0, 0, 0, 0, 0, 0, 0, 0};
char lastlineone[8] = {0, 0, 0, 0, 0, 0, 0, 0};
while(pos <= len){
pos++;
// if we have a \r followed by \n
if (((char*)uip_appdata)[pos] == ISO_nl || ((char*)uip_appdata)[pos] == ISO_cr){
if (((char*)uip_appdata)[pos] == ISO_nl || ((char*)uip_appdata)[pos-1] == ISO_cr){
if (newline == true) {
startresponsedata = true;
}
newline = true;
}
continue;
}
if (newline == true) {
linenumber++;
newline = false;
linepos = 0;
}
if (startresponsedata == true && linenumber == 0) {
linezero[linepos] = ((char*)uip_appdata)[pos];
linepos++;
}
if (startresponsedata == true && linenumber == 1) {
lineone[linepos] = ((char*)uip_appdata)[pos];
linepos++;
}
}
if (len == 7) {
linezero[0] = '7';
memcpy(lineone, uip_appdata, len);
}
Serial.print("Content length: ");
Serial.println(linezero);
Serial.print("Instances launched: ");
Serial.println(lineone);
if (len > 0 && *linezero == '7') {
lc.setChar(0, 0, ' ', false);
if (lineone[0] != lastlineone[0]) {
lc.setChar(0, 1, lineone[0], false);
}
if (lineone[1] != lastlineone[1]) {
lc.setChar(0, 2, lineone[1], false);
}
if (lineone[2] != lastlineone[2]) {
lc.setChar(0, 3, lineone[2], false);
}
if (lineone[3] != lastlineone[3]) {
lc.setChar(0, 4, lineone[3], false);
}
if (lineone[4] != lastlineone[4]) {
lc.setChar(0, 5, lineone[4], false);
}
if (lineone[5] != lastlineone[5]) {
lc.setChar(0, 6, lineone[5], false);
}
if (lineone[6] != lastlineone[6]) {
lc.setChar(0, 7, lineone[6], false);
}
memcpy(lastlineone, lineone, sizeof(lineone));
}
}
if(uip_rexmit()) {
Serial.println("SA: rexmit");
Serial.println(requestLine);
uip_send(requestLine, strlen(requestLine));
}
}
// These uIP callbacks are unused for the purposes of this simple DHCP example
// but they must exist.
void socket_app_init(void)
{
Serial.println("SAInit");
}
void udpapp_init(void)
{
Serial.println("UDPAPPINIT:");
}
void dummy_app_appcall(void)
{
Serial.println("DUMMYAPPAPPCALL");
}
}