This is a post about a work in progress…

If you’re in the transportation field, you’ve likely heard of the Bluetooth Scanners that cost around $4,000 each. These devices scan MAC (Media Access Control) addresses and log them (with the time of the scan) and use that for travel time studies or for origin-destination studies.

My question is, can we build something good-enough with an Arduino for much less money? Something like the concept below?

There’s reasons for everything:

Arduino

Controls it all and brings it together.  Turns on the GPS, Bluetooth, listens to the stream of data from both, writes to the memory card.

GPS

The Arduino has no real-time clock (meaning that unless you tell it what time it is, it doesn’t know!).  The GPS signal includes time.  It also includes position, which would be pretty useful.

Bluetooth

If we’re going to scan for Bluetooth MAC addresses, something to receive them might come in handy…

Something to Write To

Scanning the addresses would be pretty pointless without storing the data.

Initial Design

/*
Bluetooth Tracker
Written by Andrew Rohne (arohne@oki.org)
www.oki.org
*/

#include 
#include 

NewSoftSerial ol(10,11);

char inByte;
boolean ext=false;

void setup(){
  String btreturn;
  Serial.begin(115200);
  delay(1500);
  Serial.print("$$$");
  delay(1000);

}

void loop(){
  byte incomingByte=-1;
  byte index=0;
  char macaddys[160];

  while(Serial.available()>0){
    index=0;
    Serial.println("IN15");
    delay(16500);
    incomingByte=Serial.read();
    while(incomingByte>-1 && index<160){
      macaddys[index]=(char)incomingByte;
      index++;
      incomingByte=Serial.read();
    }
    if(macaddys!=""){
      Serial.end();
      writelog((String)millis()+":"+macaddys+"\r\n");
      Serial.begin(115200);
    }
  }
  if(Serial.available()<=0){
    delay(1000);
    Serial.begin(115200);
  }
    
}

void writelog(String line)
{
  ol.begin(9600);
  ol.print(line);
  ol.end();
}

The Results

The program wrote about 5kb of text to the file before dying after 489986 milliseconds (8 minutes). I had left it on a windowsill overnight (the windowsill is literally about 15 feet from Fort Washington Way in Cincinnati, which is 6 lanes (see below for the range centered on roughly where the setup was located).

There were 9 unique Bluetooth MAC addresses scanned. During the 8 minutes, there were 25 groups of MAC addresses written to the file. 5 MAC addresses appeared in multiple groups, with 3 of the MAC addresses appearing in 24 of the groups (and they may have appeared in the last group, it appears to have been cut off). Those same 4 have been seen in earlier tests, too, so I don't know what's going on there.

The Problems to Fix

Well, first there's the problem that I had let it run all night, and it only had 8 minutes of data. Something is causing the Arduino to stop writing or the OpenLog to stop operating.

In the output file, there are a few issues. First, some processing needs to be done, and second, it appears I am reading past the end of the serial buffer (if you look in the image below, you can see a lot of characters that look like a y with an umlaut).

In the code above, the IN15 command is sent to the Bluetooth Mate Gold, which tells it to inquire for 15 seconds, and then I delay for 16.5 seconds. This is because I THINK there is a delay after the scan finishes. I don't know how long that delay is. Vehicles traveling by at 65 MPH is 95.333 feet per second. Assuming I can get the Bluetooth device very close to the road, that 1.5 second gap SHOULD be okay, but if I have to go longer it could be a problem (the range of a Class 1 Bluetooth device is 313 feet, so a device can be scanned anytime in 626 feet (up to 313 feet before the Bluetooth Station and up to 313 feet after the Bluetooth station). A vehicle would be in range for about 6.6 seconds. However, the Bluetooth signal is at 2.4 - 2.485 Ghz, and is susceptible to some interference from the vehicle, driver, passengers, etc., so speed is key.

Conclusion

I'm on the fence as to whether or not the Bluetooth Mate Gold is the right way to do this. I will still be doing some research to see if I can get better speed out of it, or if I need to look into a different receiver that can receive the 2.4 GHz area and look for MAC addresses and stream them to the Arduino.

I also need to get the GPS up and running. That is a different story altogether, as I have been trying on that and have not been successful (despite using code that works for my personal Arduino and GPS, although the model of GPS 'chip' is different.

Tags: Arduino, Bluetooth, data collection, O-D Studies, technology

Posted on Friday, September 30th, 2011 By Andrew Rohne Comments are closed.