CNI widgets

Serial port scan trigger device

We are using a [Teensy board] programmed using a simple [teensyduino] sketch. The basic sketch is

/*
* CNI_trigger sketch for Arduino.
* 
* 
* A simple sketch to generate TTl pulses when told to do so through a serial
* port command.  
*
* When running this sketch on a Teensy, be sure to set the "USB Type" to
* "Serial" (under the Arduino Tools menu). 
* 
* This sketch will also listen for input pulses and send out a serial port 
* character whenever one is detected. It uses an external interrupt, so it
* can reliably detect very brief pulses. We use this to detect the GE 3.3v 
* scope trigger pulses (~4 usec pulse duration). 
* 
*
* Copyright 2011 Robert F. Dougherty.
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
* GNU General Public License for more details.
*
* You might have received a copy of the GNU General Public License
* along with this program.  If not, see <http://www.gnu.org/licenses/>.
*
*
* HISTORY:
* 2011.03.28 RFD (bobd@stanford.edu) finished a working version.
* 2011.05.24 RFD: cleaned up source & comments, removed down-counter code,
* and added a serial message upon every input pulse that's detected.
*/

#define VERSION "1.0"

// Flash library is available from http://arduiniana.org/libraries/Flash/
#include <Flash.h>
#include <Messenger.h>

#define BAUD 57600

#define DEFAULT_OUT_PULSE_MSEC 5
#define DEFAULT_IN_PULSE_STATE 0

// The approximate duration of the output pulse, in milliseconds.
// Note that we don't account for delays in the code, so it will 
// always be a bit longer than this.
unsigned int g_outPulseDuration = DEFAULT_OUT_PULSE_MSEC;

// The input pin should be the pin mapped to INT0, unless you change
// the interrupt number below. The output pin can be any digital pin.
// Teensy2.0 has LED on pin 11 and INT0 on pin 5 (D0)
#define INTERRUPT 0
const byte g_outPin = 11;
const byte g_inPin = 5;

byte g_inPulseEdge = FALLING;

volatile byte g_outPinOn = false;
volatile unsigned long g_outPulseStart;

// Instantiate Messenger object used for serial port communication.
Messenger g_message = Messenger(',','[',']');

// Create the Message callback function. This function is called whenever a complete 
// message is received on the serial port.
void messageReady() {
 int val[10];
 byte i = 0;
 if(g_message.available()) {
   // get the command byte
   char command = g_message.readChar();
   switch(command) {
   
   case '?': // display help text
     Serial << F("CNI Trigger Device\n");
     Serial << F("Sends TTL pulses out on pin ") << (int)g_outPin << F(".\n");
     Serial << F("Listens for pulses in on pin ") << (int)g_inPin << F(".\n");
     Serial << F("\nCommands:\n");
     Serial << F("[t]   will send a trigger pulse. This also disables the input pulse\n");
     Serial << F("      detection. Send a [p] command to re-enable it.\n\n");
     Serial << F("[o,N] set the output pulse duration to N milliseconds. Send with\n");
     Serial << F("      no argument to show the current pulse duration.\n\n");
     Serial << F("[p]   enable input pulse detection. Send a [t] to disable.\n\n");
     Serial << F("[r]   reset default state.\n\n");
     break;
     
   case 'o': // Set out-pulse duration (msec)
     while(g_message.available()) val[i++] = g_message.readInt();
     if(i>1){
       Serial << F("ERROR: Set output pulse duration requires no more than one param.\n");
     }else if(i==1){
         g_outPulseDuration = val[0];
     }
     Serial << F("Output pulse duration is set to ") << g_outPulseDuration << F(" msec.\n");
     break;
 
   case 't': // force output trigger
     // First force the pin low, in case it was already on. This will ensure that
     // we get a change on the pin no matter what state we were in.
     if(g_outPinOn) digitalWrite(g_outPin, LOW);
     triggerOut();
     // Automatically disable input pulse detection
     setInPulseState(0);
     break;

   case 'p': // turn on input pulse detection
     //Serial << F("Enabling input pulses\n");
     setInPulseState(1);
     break;

   case 'r': // reset
     setInPulseState(DEFAULT_IN_PULSE_STATE);
     g_outPulseDuration = DEFAULT_OUT_PULSE_MSEC;
     digitalWrite(g_outPin, LOW);
     break;

   default:
     Serial << F("[") << command << F("]\n");
     Serial << F("ERROR: Unknown command.\n\n");
   } // end switch
 } // end while
}

void setup(){
 Serial.begin(BAUD);
 Serial << F("*********************************************************\n");
 Serial << F("* CNI Trigger firmware version ") << VERSION << F("\n");
 Serial << F("* Copyright 2011 Bob Dougherty <bobd@stanford.edu>\n");
 Serial << F("* http://cniweb.stanford.edu/wiki/CNI_widgets\n");
 Serial << F("*********************************************************\n\n");
 
 // This probably isn't necessary- external interrupts work even in OUTPUT mode. 
 pinMode(g_inPin, INPUT);
 
 pinMode(g_outPin, OUTPUT);
 digitalWrite(g_outPin, LOW);
 setInPulseState(DEFAULT_IN_PULSE_STATE);
 
 // Attach the callback function to the Messenger
 g_message.attach(messageReady);
 
 Serial << F("CNI Trigger Ready. Send the ? command ([?]) for help.\n\n");
}

void loop(){
 // Reset the output, if needed:
 if(g_outPinOn){
   // Turn off the output pin after the requested duration.
   // Detect and correct counter wrap-around:
   if(millis()<g_outPulseStart) g_outPulseStart += 4294967295UL;
   if(millis()-g_outPulseStart > g_outPulseDuration)
     digitalWrite(g_outPin, LOW);
 }
   
 // Handle Messenger's callback:
 if(Serial.available())  g_message.process(Serial.read());
}

void setInPulseState(byte state){
 // Turn on the internal pull-up resistor if we want to detect falling edges.
 if(g_inPulseEdge==FALLING)
   digitalWrite(g_inPin, HIGH);
 else
   digitalWrite(g_inPin, LOW);
 // Attach or detach the interrupt
 if(state)
   attachInterrupt(INTERRUPT, triggerIn, g_inPulseEdge);
 else
   detachInterrupt(INTERRUPT);
}

// The following is an interrupt routine that is run each time the 
// a pulse is detected on the trigger input pin.
void triggerIn(){
 Serial << F("p");
}

void triggerOut(){
   digitalWrite(g_outPin, HIGH);
   g_outPinOn = true;
   g_outPulseStart = millis();
   //Serial << F("OUT\n");
}

GE physiological data monitor

Circuit tidbits

RS232 level converter

We need a little circuit to take the scanner data stream (-12v to +12v) and allow it to be safely ready by our 5v microprocessor. We just took the Tx part of this simple RS232 level converter. We used a 2N3904 transistor with emitter to ground, collector to the UART Rx pin on the microcontroller with a 10k pull-up resistor to the 5v line, and the base connected to the Tx line coming from the scanner via a 4.7K resistor, with a 4.7k pull-down to ground.