bme280 board. Does it need external pullups?

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linuxgeek

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I'm using this bme280 board from diymall. I'm not clear if it already has pullup resistors from the schematic. I'm attaching it.

I have it working with external pullups on a breadboard, but now that I want to assemble it, I'm wondering if I should remove the external pullups.

GY-BME280-SCH.jpgGY-BME280.jpg
 
It has internal 10k pull-up resistors from the schematic. The question is if that is sufficient for a longer wiring length and it depends also from the data rate. Just give it a try and check the signals (the quality of the rising and falling ramps with an oscilloscope). With that, it is easy to optimize the pull up resistor value to kind of match the line impedance.
 
Thanks!

I did have it set at 400kHz, but I imagine I don't need that. I'll put it at 100kHz and try that with the internal pullups. My cable length will only be about a cm or 2.
 
I have another very similar question along this line.

I am working with some different bmp280 modules. These are the best pictures i saw available from various sources.

View attachment 8536
5pcs-GY-BMP280-3-3-High-Precision-Atmospheric-Pressure-Sensor-Module-for-Arduino-Free-Shipping.jpg

I can get it to connect and output values, but it's pretty finicky even with wire @ 100kHz.

It's on a breadboard so maybe it would be better hardwired together. But I can usually get it to work, but if I breathe on with some warm humid air it will stop responding. I assume it's on the edge for a good resistor value.

Counter-intuitive to me, but if I put a an additional external 3.3k ohm resistor between SCL<->VCC and SDA<->VCC, it's much more stable in that breathing on it no longer causes it to stop responding. Although instability is not totally gone.

I can see that the resistors on the module say 103, so that's the 10k resistor. I wonder if it's feasible to unsolder them and change them to 4.7k resistors, or something a little lower. Is there anything I can do with external resistors to the module to make it more stable?

Even when it does run fairly stable, after a few minutes it will start spitting out values that are nonsensical, so I assume the timing has gotten weird.

Thanks for any tips in advanced.
 

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Yeah, seems like replacing those 10K resistors should be fine. But maybe there's some other problem going on here?

Can you try running Teensy at 24 MHz? That's still faster than normal Arduino, but not nearly as much. Maybe there's some other timing requirements which are normally met by AVR's slow performance? We saw this with those Lidar devices, where even with proper I2C protocol, accessing the device too soon caused problems.

Where did you get these particular sensor modules? I could order one and put it on my list of stuff to test....
 
24Mhz didn't seem to help. I'm using i2c_t3.

I've used various code, but I usually use onehorse's code from one of his boards that has a bmp280 to make sure it's working.

I got them here as a 10-pack: http://www.ebay.com/itm/10pcs-High-Precision-GY-BMP280-3-3-Pressure-Sensor-Board-Module-for-Arduino-/151854550869

But I think generally, if you search for GY-BMP280 you'll find essentially the same board. It was cheaper to get these modules than the actual sensor by itself, so I could hardly resist. The module seemed simple enough that I was hoping there would be no issues with them.

Should be the same as this one: https://www.amazon.com/Wrisky-GY-BMP280-3-3-Pressure-Precision-Atmospheric/dp/B01KZ6S06O

I should probably create the most minimalist code for testing. I can do that and post it.

Oh, and I've used about 4 different modules with a bmp280 or bme280, and have been able to get them to run. Maybe I should test other modules again and make sure. Thanks.
 
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I soldered some more modules to test, and it's still problematic. The adafruit ones work without a problem.

If I understand it correctly, can I just remove the resistors on the module, and put my own external resistors on the breadboard? I assume the SDA and SCL are still connected to the header holes.

Also, can I remove the capacitors in case there's still a problem? I assume I can just remove them and not bother bridging across where the capacitor used to be. Is that right?

Here's the adafruit one:

sensors_2651_iso_ORIG.jpgsensors_sch.jpg
 
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Is it possible the cheap modules are a counterfeit BMP280 or overrun, like extra inventory which failed quality testing?
 
Doesn't seem likely to be counterfeit. Looks just like my other bmp280s and it does output very sensitively to pressure as expected. Could be failed units tho.

Will what I suggested work? Or should I just wire up directly to the contact points on the bmp280?
 
I doubt this means much, but the adafruit ones have an i2c address of 0x77, but the ones not working are 0x76.

It's supposed to be 0x76, but adafruit ones must wire it slightly differently. I believe you can connect one of the points to GND or VCC to shift it by 1.
 
I tried removing the resistors but no luck. Something very strange is going on.

Tried a T3.2 and a TLC.

I just spent the last hour trying to figure out why the voltage was creeping up on my boards, until I noticed that the battery was low on my multimeter! Never thought about that before. At least I can stop worrying that somehow I was destroying every device with USB that I touched! LOL. When it happened with a USB wall charger, I knew something was not right with the world. It started to dawn on me when USB voltage was rising above 6 volts, which seemed unlikely without things getting very hot.

Just realized I was trying pin 22/23 on a T3.2, which doesn't have i2c on those ports.

Do I need to use only Wire1 with pin 22/23? And only Wire with pin 16/17, 18/19. If so, I guess the library doesn't complain about that. And if that's the case, does that mean T3.2, you have to use underpads 29/30 for Wire1?
 
Do I need to use only Wire1 with pin 22/23? And only Wire with pin 16/17, 18/19. If so, I guess the library doesn't complain about that. And if that's the case, does that mean T3.2, you have to use underpads 29/30 for Wire1?
Yes. Unfortunately, the current Teensy 1.31 beta1 release does not provide Wire1. In order to use Wire1, you currently have to use the alternative i2c_t3.h library, which provides all of the appropriate Wire headers. You then have to clone your libraries to include i2c_t3.h instead of Wire.h (and you have to be sure you use all of the cloned libraries).

Alternatively, you can put a fake Wire.h in your local library headers and use i2c_t3.h under the covers.

In addition to using i2c_t3.h, some people have modified some libraries to have constructors that take an additional argument to use the appropriate Wire header.

I have an idea of how to add support for multiple i2c ports without having to modify the libraries (but you would have to modify the Wire/i2c_t3 libraries).

Basically add a remap function to Wire<n> that takes 3 arguments:
  • An i2c address to remap
  • A Wire<n> address to call for functions using that address
  • An i2c address to use when the address is remapped

The i2c header would have the remap table, and each i2c class function would have tests of the following:
Code:
void TwoWire::begin(uint8_t address)
{
[COLOR="#008000"]        if (remap[address].wire_header != NULL)
            return remap[address].wire_header->begin (address);[/COLOR]

        begin();
        I2C0_A1 = address << 1;
        slave_mode = 1;
        I2C0_C1 = I2C_C1_IICEN | I2C_C1_IICIE;
        NVIC_ENABLE_IRQ(IRQ_I2C0);
}

This would allow you to use all 4 of the i2c buses on the Teensy 3.6 (and 3 on the Teensy 3.5, and 2 on the Teensy 3.1/3.2/LC) using standard libraries. You would have 255 addresses you could use (since the basic i2c address type is uint8_t).
 
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I moved the sensor to pin 16/17 and used Wire, not Wire1.

Every so often, it seems to be working, but then it starts to misbehave. I think you're right, that the BMP280s were probably to be discarded but resold.
 
I am using i2c_t3, so that shouldn't be a problem. I just didn't think about the pins being hardwared to Wire or Wire1.

Here's the code that I attempted to clean up a bit to make it just for bmp280.

Code:
/* BNO055_BMP280_t3 Basic Example Code
 by: Kris Winer
 date: April 25, 2015
 license: Beerware - Use this code however you'd like. If you 
 find it useful you can buy me a beer some time.

 adapted for minimalist testing BMP280 purposes
 
 It uses SDA/SCL on pins 17/16, respectively, and it uses the Teensy 3.1-specific Wire library i2c_t3.h.
 
 The Add-on shield can also be used as a stand-alone breakout board for any Arduino, Teensy, or 
 other microcontroller by closing the solder jumpers on the back of the board.
  
 The BMP280 is a simple but high resolution (20-bit) pressure sensor, which can be used in its high resolution
 mode but with power consumption of 20 microAmp, or in a lower resolution mode with power consumption of
 only 1 microAmp. The choice will depend on the application.
 
 All sensors communicate via I2C at 400 Hz or higher.
 SDA and SCL should have external pull-up resistors (to 3.3V).
 4K7 resistors are on the BNO055_BMP280 breakout board.
 
 Hardware setup:
 Breakout Board --------- Arduino/Teensy
 3V3 ---------------------- 3.3V
 SDA -----------------------A4/17
 SCL -----------------------A5/16
 GND ---------------------- GND
 
 Note: The BNO055_BMP280 breakout board is an I2C sensor and uses the Arduino Wire or Teensy i2c_t3.h library. 
 Because the sensor is not 5V tolerant, we are using a 3.3 V 8 MHz Pro Mini or a 3.3 V Teensy 3.1.
 We have disabled the internal pull-ups used by the Wire library in the Wire.h/twi.c utility file.
 We are also using the 400 kHz fast I2C mode by setting the TWI_FREQ  to 400000L /twi.h utility file.
 The Teensy has no internal pullups and we are using the Wire.begin function of the i2c_t3.h library
 to select 400 Hz i2c speed.
 */
 
//#include <Wire.h>   
#include <i2c_t3.h>
//#include <kinetis.h>

// BMP280 registers
#define BMP280_TEMP_XLSB  0xFC
#define BMP280_TEMP_LSB   0xFB
#define BMP280_TEMP_MSB   0xFA
#define BMP280_PRESS_XLSB 0xF9
#define BMP280_PRESS_LSB  0xF8
#define BMP280_PRESS_MSB  0xF7
#define BMP280_CONFIG     0xF5
#define BMP280_CTRL_MEAS  0xF4
#define BMP280_STATUS     0xF3
#define BMP280_RESET      0xE0
#define BMP280_ID         0xD0  // should be 0x58
#define BMP280_CALIB00    0x88

#define BMP280_ADDRESS 0x76   // Address of BMP280
//#define BMP280_ADDRESS 0x77   // Address of BMP280 adafruit

#define SerialDebug true      // set to true to get Serial output for debugging

enum Posr {
  P_OSR_00 = 0,  // no op
  P_OSR_01,
  P_OSR_02,
  P_OSR_04,
  P_OSR_08,
  P_OSR_16
};

enum Tosr {
  T_OSR_00 = 0,  // no op
  T_OSR_01,
  T_OSR_02,
  T_OSR_04,
  T_OSR_08,
  T_OSR_16
};

enum IIRFilter {
  full = 0,  // bandwidth at full sample rate
  BW0_223ODR,
  BW0_092ODR,
  BW0_042ODR,
  BW0_021ODR // bandwidth at 0.021 x sample rate
};

enum Mode {
  BMP280Sleep = 0,
  forced,
  forced2,
  normal
};

enum SBy {
  t_00_5ms = 0,
  t_62_5ms,
  t_125ms,
  t_250ms,
  t_500ms,
  t_1000ms,
  t_2000ms,
  t_4000ms,
};

// Specify BMP280 configuration
//uint8_t Posr = P_OSR_16, Tosr = T_OSR_02, Mode = normal, IIRFilter = BW0_042ODR, SBy = t_62_5ms; // set pressure amd temperature output data rate
uint8_t Posr = P_OSR_16, Tosr = T_OSR_02, Mode = normal, IIRFilter = full, SBy = t_00_5ms; 
// t_fine carries fine temperature as global value for BMP280
int32_t t_fine;
  
// Pin definitions
//int intPin = 8;  // These can be changed, 2 and 3 are the Arduinos ext int pins
//int myLed = 13;

uint16_t Pcal[8];         // calibration constants from BMP280 PROM registers
uint32_t D1 = 0, D2 = 0;  // raw BMP280 pressure and temperature data
double Temperature, Pressure;        // stores BMP280 pressures sensor pressure and temperature
int32_t rawPress, rawTemp;   // pressure and temperature raw count output for BMP280

// BMP280 compensation parameters
uint16_t dig_T1, dig_P1;
int16_t  dig_T2, dig_T3, dig_P2, dig_P3, dig_P4, dig_P5, dig_P6, dig_P7, dig_P8, dig_P9;

int msec = 50, delt_t=0, count=0;
float sec = 0.0;

void setup()
{
  // Setup for Master mode, pins 16/17, external pullups, 400kHz for Teensy 3.1
  Wire.begin(I2C_MASTER, 0x00, I2C_PINS_16_17, I2C_PULLUP_EXT, I2C_RATE_100);
//Wire.begin(I2C_MASTER, 0x00, I2C_PINS_18_19, I2C_PULLUP_EXT, I2C_RATE_100);
  delay(1000);
  Serial.begin(38400);
  while (!Serial) delay(1000);
  
//  pinMode(myLed, OUTPUT);
//  digitalWrite(myLed, HIGH);

  I2Cscan(); // check for I2C devices on the bus8
  delay(1000);
  
  // Read the WHO_AM_I register of the BMP280 this is a good test of communication
  byte f = readByte(BMP280_ADDRESS, BMP280_ID);  // Read WHO_AM_I register for BMP280
  Serial.print("BMP280 "); 
  Serial.print("I AM "); 
  Serial.print(f, HEX); 
  Serial.print(" I should be "); 
  Serial.println(0x58, HEX);
  Serial.println(" ");
  delay(1000); 

  writeByte(BMP280_ADDRESS, BMP280_RESET, 0xB6); // reset BMP280 before initilization
  delay(1000);

  BMP280Init(); // Initialize BMP280 altimeter
  Serial.println("Calibration coeficients:");
  Serial.print("dig_T1 ="); 
  Serial.println(dig_T1);
  Serial.print("dig_T2 ="); 
  Serial.println(dig_T2);
  Serial.print("dig_T3 ="); 
  Serial.println(dig_T3);
  Serial.print("dig_P1 ="); 
  Serial.println(dig_P1);
  Serial.print("dig_P2 ="); 
  Serial.println(dig_P2);
  Serial.print("dig_P3 ="); 
  Serial.println(dig_P3);
  Serial.print("dig_P4 ="); 
  Serial.println(dig_P4);
  Serial.print("dig_P5 ="); 
  Serial.println(dig_P5);
  Serial.print("dig_P6 ="); 
  Serial.println(dig_P6);
  Serial.print("dig_P7 ="); 
  Serial.println(dig_P7);
  Serial.print("dig_P8 ="); 
  Serial.println(dig_P8);
  Serial.print("dig_P9 ="); 
  Serial.println(dig_P9);

  Serial.flush();
  delay(2000);
  }

void loop()
{  
  delt_t = millis() - count;
  if (delt_t > msec) { // update based on delt_t
    rawPress =  readBMP280Pressure();
    Pressure = (float) bmp280_compensate_P(rawPress)/25600.; // Pressure in mbar
    rawTemp =   readBMP280Temperature();
    Temperature = (float) bmp280_compensate_T(rawTemp)/100.;

    float altitude = 145366.45f*(1.0f - pow((Pressure/1013.25f), 0.190284f));

    if(SerialDebug) {
      Serial.println("BMP280:");
      Serial.print("Altimeter temperature = "); 
      Serial.print( Temperature, 2); 
      Serial.println(" C"); // temperature in degrees Celsius
      Serial.print("Altimeter temperature = "); 
      Serial.print(9.*Temperature/5. + 32., 2); 
      Serial.println(" F"); // temperature in degrees Fahrenheit
      Serial.print("Altimeter pressure = ");
 
      Serial.println(Pressure, 6);
      /*      
      Serial.println(" mbar");// pressure in millibar
      Serial.print("Altitude = "); 
      Serial.print(altitude, 2); 
      Serial.println(" feet");
      Serial.println(" ");
      */
    }
//    digitalWrite(myLed, !digitalRead(myLed));
    count = millis();
    sec += (msec/1000.0);
    Serial.print("sec: ");
    Serial.println(sec);
    }
}

int32_t readBMP280Temperature() {
  uint8_t rawData[3];  // 20-bit pressure register data stored here
  readBytes(BMP280_ADDRESS, BMP280_TEMP_MSB, 3, &rawData[0]);  
  return (int32_t) (((int32_t) rawData[0] << 16 | (int32_t) rawData[1] << 8 | rawData[2]) >> 4);
}

int32_t readBMP280Pressure() {
  uint8_t rawData[3];  // 20-bit pressure register data stored here
  readBytes(BMP280_ADDRESS, BMP280_PRESS_MSB, 3, &rawData[0]);  
  return (int32_t) (((int32_t) rawData[0] << 16 | (int32_t) rawData[1] << 8 | rawData[2]) >> 4);
}

void BMP280Init()
{
  // Configure the BMP280
  // Set T and P oversampling rates and sensor mode
  writeByte(BMP280_ADDRESS, BMP280_CTRL_MEAS, Tosr << 5 | Posr << 2 | Mode);
  // Set standby time interval in normal mode and bandwidth
  writeByte(BMP280_ADDRESS, BMP280_CONFIG, SBy << 5 | IIRFilter << 2);
  // Read and store calibration data
  uint8_t calib[24];
  readBytes(BMP280_ADDRESS, BMP280_CALIB00, 24, &calib[0]);
  dig_T1 = (uint16_t)(((uint16_t) calib[1] << 8) | calib[0]);
  dig_T2 = ( int16_t)((( int16_t) calib[3] << 8) | calib[2]);
  dig_T3 = ( int16_t)((( int16_t) calib[5] << 8) | calib[4]);
  dig_P1 = (uint16_t)(((uint16_t) calib[7] << 8) | calib[6]);
  dig_P2 = ( int16_t)((( int16_t) calib[9] << 8) | calib[8]);
  dig_P3 = ( int16_t)((( int16_t) calib[11] << 8) | calib[10]);
  dig_P4 = ( int16_t)((( int16_t) calib[13] << 8) | calib[12]);
  dig_P5 = ( int16_t)((( int16_t) calib[15] << 8) | calib[14]);
  dig_P6 = ( int16_t)((( int16_t) calib[17] << 8) | calib[16]);
  dig_P7 = ( int16_t)((( int16_t) calib[19] << 8) | calib[18]);
  dig_P8 = ( int16_t)((( int16_t) calib[21] << 8) | calib[20]);
  dig_P9 = ( int16_t)((( int16_t) calib[23] << 8) | calib[22]);
}

// Returns temperature in DegC, resolution is 0.01 DegC. Output value of
// “5123” equals 51.23 DegC.
int32_t bmp280_compensate_T(int32_t adc_T)
{
  int32_t var1, var2, T;
  var1 = ((((adc_T >> 3) - ((int32_t)dig_T1 << 1))) * ((int32_t)dig_T2)) >> 11;
  var2 = (((((adc_T >> 4) - ((int32_t)dig_T1)) * ((adc_T >> 4) - ((int32_t)dig_T1))) >> 12) * ((int32_t)dig_T3)) >> 14;
  t_fine = var1 + var2;
  T = (t_fine * 5 + 128) >> 8;
  return T;
}

// Returns pressure in Pa as unsigned 32 bit integer in Q24.8 format (24 integer bits and 8
//fractional bits).
//Output value of “24674867” represents 24674867/256 = 96386.2 Pa = 963.862 hPa
uint32_t bmp280_compensate_P(int32_t adc_P)
{
  long long var1, var2, p;
  var1 = ((long long)t_fine) - 128000;
  var2 = var1 * var1 * (long long)dig_P6;
  var2 = var2 + ((var1*(long long)dig_P5)<<17);
  var2 = var2 + (((long long)dig_P4)<<35);
  var1 = ((var1 * var1 * (long long)dig_P3)>>8) + ((var1 * (long long)dig_P2)<<12);
  var1 = (((((long long)1)<<47)+var1))*((long long)dig_P1)>>33;
  if(var1 == 0)
  {
    return 0;
    // avoid exception caused by division by zero
  }
  p = 1048576 - adc_P;
  p = (((p<<31) - var2)*3125)/var1;
  var1 = (((long long)dig_P9) * (p>>13) * (p>>13)) >> 25;
  var2 = (((long long)dig_P8) * p)>> 19;
  p = ((p + var1 + var2) >> 8) + (((long long)dig_P7)<<4);
  return (uint32_t)p;
}

// I2C scan function

void I2Cscan() {
// scan for i2c devices
  byte error, address;
  int nDevices;

  Serial.println("Scanning...");

  nDevices = 0;
  for(address = 1; address < 127; address++ ) 
  {
    // The i2c_scanner uses the return value of
    // the Write.endTransmisstion to see if
    // a device did acknowledge to the address.
    Wire.beginTransmission(address);
    error = Wire.endTransmission();

  Serial.print("I2C address: ");
  Serial.println(address);

    if (error == 0)
    {
      Serial.print("I2C device found at address 0x");
      if (address<16) 
        Serial.print("0");
      Serial.print(address,HEX);
      Serial.println("  !");

      nDevices++;
    }
    else if (error==4) 
    {
      Serial.print("Unknow error at address 0x");
      if (address<16) 
        Serial.print("0");
      Serial.println(address,HEX);
    }    
  }
  if (nDevices == 0)
    Serial.println("No I2C devices found\n");
  else
    Serial.println("done\n");
}

// I2C read/write functions

  void writeByte(uint8_t address, uint8_t subAddress, uint8_t data) {
    Wire.beginTransmission(address);  // Initialize the Tx buffer
    Wire.write(subAddress);           // Put slave register address in Tx buffer
    Wire.write(data);                 // Put data in Tx buffer
    Wire.endTransmission();           // Send the Tx buffer
  }

  uint8_t readByte(uint8_t address, uint8_t subAddress) {
    uint8_t data; // `data` will store the register data   
    Wire.beginTransmission(address);         // Initialize the Tx buffer
    Wire.write(subAddress);                  // Put slave register address in Tx buffer
    Wire.endTransmission(I2C_NOSTOP);        // Send the Tx buffer, but send a restart to keep connection alive
    //  Wire.endTransmission(false);             // Send the Tx buffer, but send a restart to keep connection alive
    //  Wire.requestFrom(address, 1);  // Read one byte from slave register address 
    Wire.requestFrom(address, (size_t) 1);   // Read one byte from slave register address 
    data = Wire.read();                      // Fill Rx buffer with result
    return data;                             // Return data read from slave register
  }

   void readBytes(uint8_t address, uint8_t subAddress, uint8_t count, uint8_t * dest) {  
    Wire.beginTransmission(address);   // Initialize the Tx buffer
    Wire.write(subAddress);            // Put slave register address in Tx buffer
    Wire.endTransmission(I2C_NOSTOP);  // Send the Tx buffer, but send a restart to keep connection alive
    //  Wire.endTransmission(false);       // Send the Tx buffer, but send a restart to keep connection alive
    uint8_t i = 0;
    //        Wire.requestFrom(address, count);  // Read bytes from slave register address 
    Wire.requestFrom(address, (size_t) count);  // Read bytes from slave register address 
    while (Wire.available()) {  // Put read results in the Rx buffer
      dest[i++] = Wire.read();
    }        
}
 
I thought I'd just update this. I think out of my 10 bmp280 modules, the first 3 were bad. I have one working now that is running fine.

Oddly, soon after I ordered these, my ebay account was locked. I wasn't able to purchase any longer, and not get a refund, and I'm guessing I might not have been able to review the vendor anymore either. BTW, when your ebay account is locked, there's basically no explanation and no recourse with ebay AFAICT. I had to create a new account to do my next purchase. I'm just wondering if there's something the sellers can do to lock the account of a buyer, cause I'm wondering how some of the ebay sellers can stay at 99% favorability rating.

At some point I might try and replace the bmp280 sensor on the module, since I have a few of those around.
 
I thought I'd just update this. I think out of my 10 bmp280 modules, the first 3 were bad. I have one working now that is running fine.

Oddly, soon after I ordered these, my ebay account was locked. I wasn't able to purchase any longer, and not get a refund, and I'm guessing I might not have been able to review the vendor anymore either. BTW, when your ebay account is locked, there's basically no explanation and no recourse with ebay AFAICT. I had to create a new account to do my next purchase. I'm just wondering if there's something the sellers can do to lock the account of a buyer, cause I'm wondering how some of the ebay sellers can stay at 99% favorability rating.

At some point I might try and replace the bmp280 sensor on the module, since I have a few of those around.

I bought some of these on ebay too-the purple ones. The pressure variation between them was quite high, around 4hpa and not close to the pressure reported by my local weather station. An adafruit bmp 180 gave pressures that were spot on. I think these boards are cheap because they're using reject sensors. No good for my application but maybe okay for some.
 
Interesting. You're probably right. Hopefully I can replace the sensor reliably without destroying it. I wish they would sell it without the sensor, then I could just put the sensor on which wouldn't be too hard I think.
 
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