[AC_Hacker]

More progress to report...

Trying to send analog voltage from Telair to Teensy PWM pin.

Scaled the 1024 step analog read to 256 step PWM write.

int CO2_Read = 38;                  // initialize pin 38 for input of analog voltage
int PWM_feed = 14;                  // initialize Teensy pin 14 for PWM

 
void setup()   {                    // BEGIN SETUP
  pinMode(PWM_feed, OUTPUT);        // Make Brightness (AKA: pin 14) an output pin
  int CO2_Read = 0;                 // variable set to zero
  int PWM_feed = 0;                 // variable set to zero               
  Serial.begin(38400);
}                                   // END SETUP

int CO2_volt = 0;

void loop()               
{                                   // BEGIN LOOP
  CO2_volt = analogRead(CO2_Read);  // read the Teensy input pin 38
  PWM_feed = (CO2_volt/4);        // PWM out takes the value of CO2 volt divided
  Serial.print("PWM_feed is = ");   // print val to serial monitor
  Serial.println(PWM_feed);
  delay(1000);			    // delay 1 second before repeating loop
}                                   // END LOOP

Which yielded this result:

Then I was really interested in using setup to actually power a fan, to get some idea if this was actually feasible.

I knew that the output from the Teensy pins was pretty puny, but trying to attach ANYTHING more than an LED led to disappointment.

So I learned about various Power MOSFET transistors, as the solution. I discovered that the choices of MOSFETS that can directly interface with Teensy is fairly limited, because most MOSFETs need at least a 10v pulse to turn on the transistor, but the Teensy only has 5 volts.

I did find out that these will work:

• RFP30N06LE
• IRL540
• IRLZ44N
• ST95N2LH5
• IRF520

... but nobody in this city has one. So I ordered 10 of the RFP30N06LE from Sparkfun... (wait a week)

I also found out that you can build a single transistor amplifier to kick the 5 volt output up to 10 volt(+) levels, which I did until the real thing arrives.

I also discovered that the single transistor amp inverts the signal, so I wrote a line of code that inverted the pulse, and I'm in business.

int CO2_Read = 38;                  // initialize pin 38 for analog voltage in
int PWM_pin = 14;                   // initialize pin 14 for PWM

 
void setup()   {                    // BEGIN SETUP
  pinMode(PWM_pin, OUTPUT);         // Make PWM_pin (AKA: pin 14) an output pin
  int CO2_Read = 0;                 // variable set to zero
  int PWM_pin = 0;                  // variable set to zero               
  //Serial.begin(38400);
}                                   // END SETUP

int CO2_volt = 0;
int PWM_feed = 0;
int DutyCycle = 0;
int PWM_invert = 0;

void loop()               
{                                   // BEGIN LOOP
  CO2_volt = analogRead(CO2_Read);  // read the Teensy input pin 38
  PWM_feed = CO2_volt/4;            // Scale CO2_volts (1024) to PWM (256)
  PWM_invert = 256 - PWM_feed;  // Invert PWM_feed
  //analogWrite(PWM_pin, PWM_feed);
  analogWrite(PWM_pin, PWM_invert);
  Serial.print("PWM_feed is = ");   // print val to serial monitor
  Serial.print(PWM_feed);
  //DutyCycle = PWM_feed/256;
  DutyCycle = CO2_volt/10 ;
  Serial.print(" and duty cycle = ");
  Serial.print(DutyCycle);
  Serial.println("%");

  delay(1000);			    // delay 1 second before repeating loop
}                                   // END LOOP

See fan spin!

HRV controlled by CO2 - YouTube

Many thanks to the very helpful dorks at DorkbotPDX, you guys helped me a bunch!

Best,

-AC_Hacker