TSL2561 Digital Luminosity Sensor Wire Distance

[garybronson]

How long can the cable be between the sensor and the controller? Is it possible to place the sensor say 100 feet away and connect it with CAT5E back to the controller and have it work?

Also maybe another topic: The datasheet says i have 3 slave addresses. Does this mean i have a limit of only 3 TSL2561's per I2C connection?

Thanks

[adafruit_support_bill]

100 feet is long for an i2c bus. But not impossible. You may need to slow down the i2c clock rate or add buffers to get reliable transmission over that distance:
http://www.nxp.com/documents/leaflet/75016081.pdf

And yes. You can have as many as three of these devices on the bus.

[garybronson]

Good link. Thanks for sending that along.

As for the 3 devices question. I guess I was hoping I could somehow have more than 3. I assume this is not possible correct? In case you ask why i would need more, I'm actually trying to monitor individual LEDs on a circuit board to know if they are on or off. I am providing this information in case I may be using the wrong device in the first place for what I'm trying to accomplish. For this project I cannot tamper with the circuit board in any way so watching the LEDs provides enough information for my purposes and there will be no surrounding ambient light. In other words there is a cover that keeps everything in the dark.

I would appreciate any suggestions from sensor experts on this.

[adafruit_support_bill]

There are some tricks you could use to multiplex the bus, or even hack the library to use 'soft i2c'. But the TSL2561 is a bit of overkill for just detecting LEDs. You might consider using something like MCP23017s and some photodetectors. That would cost less, require less code and give you quite a lot of expandability.
https://www.adafruit.com/product/732

[garybronson]

Thanks for the tip. When you say photodetectors, are you referring to photoresistors or some other type of sensor?

[adafruit_support_bill]

It could be done with a photo-resistor or a photo-diode. With a photo-resistor, you would create a variable voltage divider:



You may need to experiment a bit. The value of the fixed resistor (shown as 10K in the diagram) should be selected so that the output voltage is above the logic HIGH threshold (~2.7v) when the LED is lit and below the logic LOW threshold (~0.5v) when it is off.

https://learn.adafruit.com/photocells/using-a-photocell