I've the VCNL 4000 Proximity Sensor I use some sample code and at the very beginning

the following code hangs (never finishes)

 readVCNLByte(0x81); is called

Can this problem be caused because the contact of the pin isn't very good.

I only but the part with pins in the sensor without to solder it.

Is it likely that this may be the problem ? I have not many experince with solder and the sensor is really small so i'd like to avoid it for first tests ;)

Here the code. The last output in the Serial window is "pre product"

  Serial.println("pre product");
  uint8_t rev = read8(VCNL4000_PRODUCTID);
   Serial.println("post product");
  if ((rev & 0xF0) != 0x10) {
    Serial.println("Sensor not found :(");
    while (1);



enter image description here

  • Try applying some lateral force to the connection. Or just solder the headers. It's not that hard to desolder them, if you remove the black plastic, before desoldering.
    – Gerben
    Commented Jan 14, 2015 at 19:18

2 Answers 2


You really can't expect this to work unsoldered. The contacts will be at best intermittent, and poor contact. Even a 'dry joint' where the pin is mostly surrounded by solder doesn't work well, these are the ultimate examples! You could however use an edge-connector, if you can find one; not something you see often nowadays.


Sorry .. my answer comes late .. I had the same issue, this has nothing to do with bad connexion between wires (not only at least). But by playing with some parameter (current value > 60mA) I noticed that the module begin to freeze more often. To fix that : You need to add a small delay within your readbyte function after a i2c.stop()

I found that an issue had been written about that : https://github.com/adafruit/VCNL4000/issues/1 They recommand a 170us delay

I'm testing myself at full current and max speed (an since 30min it didn't freeze)... Before it could freeze in a second.

Hope it helps ;)

EDIT : In order to better understand where the freeze comes from, I re-write a simple I2C library. I could get rid of the freeze by simple add a small delay in the i2c_start function (that send the start condition along with the slave address)

uint8_t i2c_start(uint8_t i2c_slave_address){
       //reset TWI control register
       TWCR = 0;
       //transmit start condition 
       TWCR = (1<<TWINT) | (1<<TWSTA) | (1<<TWEN);
       //wait for end of transmission
       while((TWCR & (1<<TWINT))==0){
              _delay_us(75); // <-- here is the trick
       if( (TWSR & 0xF8)!= TW_START ){
              return -1;
       // load slave address into data register
       TWDR = i2c_slave_address;
       //start address transmission
       TWCR = (1<<TWINT) | (1<<TWEN);
       //wait for transmission
       while ( (TWCR & (1<<TWINT))==0 );
       //check if the slave did acknoledge the Read/Write mode
       uint8_t twst = TW_STATUS & 0xF8;
       if ( (twst != TW_MT_SLA_ACK) && (twst != TW_MR_SLA_ACK) ){
               return -1;
       return 0;

you will need to add these libraries : util/twi.h (for the macro TW_STATUS .. TTW_MT_SLA_ACK and so on)


stdlib.h (for the uint8_t way of typing variable ..not actually 100% sure)

I'm still not fully satisfy by this solution, but it is still more effective that the one that adafruit propose.

I suggest you write you own i2c library (5 functions : init / start / read / write / stop) you now have the start already .. so 4 left ;)

If you're still to much afraid : in twi.c ( .\arduino\avr\libraries\Wire\utility\twi.c) and twi_readFrom(...) function. On line 155 and 159 you will see that arduino send the start condition, but do not wait / take care that the transmission as been done... you can add a while function as previously describe to ensure it.


My previous solution didn't solve the issue neither... Actually reading the application note (Designing VCNL4000 into an Application : google that) gives the solution (page 7) enter image description here

after you send the command to perform a single measurement, you need to wait. I put a delay of 500ms and have none anywhere else. This works like a charm.

But for energy efficiency I recommend to put the uC in sleep mode for that period of time.

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