Trouble analogReading TAOS TSL257LF photodiode

I have a TSL257LF with GND, 3.3V, and output connected to A0 of my arduino. The test sketch is loop() with Serial.println(analogRead(A0)) that in Serial Monitor shows numbers 674 to 677 oblivious to the sensor being illuminated or in darkness.

I tried another TSL257LF, putting a 10k pull-up resistor on output, and using 5VDC all to no avail.

I haven't added a decoupling cap (.1uF) to the supply lines yet, but I don't think that should be such a factor.

I'm just trying to quickly detect transitions from light to dark and the TSL257 should be faster than any LDR.

Please help.

I am also having problems with a TAOS (now AMS) TSL-257 LF sensor.

I have an Arduino one, and I am trying to read a LED from an electrical meter. First I bougth a TSL 260R-LF, and it worked pretty nice: I was able to catch LED pulses and count them, using interruptions.

However with the real LED of an electrical meter the light intensity is much lower and I couldn't catch the pulses, I learnt also that the TSL-260R phototransistor is intended for Infrared frecuencies!, I was not using the proper sensor.

Therefore I bought four TSL-257 LF Phototransistor, the recomendded phototransistor at the web site, but none of them are working like the TSL-260R. This is my configuration:

|500x375 sube fotos

I simply connect the +5Vdc supply (+3,3Vdc is also accepted according the TSL257 datasheet), the ground and finally the digital output, to the D2 pin, but I don get any signal at all.

I also tried connecting the Phototransistor output to an analog input, reading a value around 1000, that means the output is usally in a high state (+5Vdc aprox.), but never changes.

Any help?

These devices are really easy to use. Read the data sheet. First, it's a photodiode with transimpedance amplifier, not a phototransistor. The 10K load resistor

10k pull-up resistor on output

goes from ground to output. If the output never changes it might be saturated - these devices are extremely sensitive and any light leakage will saturate. Just three pins, can't go wrong unless they are the wrong way round. There are a lot of variations (part numbers) for these - generally "R" is the IR version and comes in a black package, the visible version is a clear package. Looking at the photo set-up, it will be permanently saturated. Also can't see any load resistors unless well-hidden. Have you tried it with a DMM and in a really light-proof box? Difficult to go wrong with these.

Thank you, this is exactly what was happening: the photodiode was always providing +5V, because It was in a bright environment. I did not cover it, and it was working as expected.

As soon as I covered and hid the photodiode I was able to start catching the led pulses.

I was a little bit confused because my previous IR (Infrared version) did not need to be covered, to stay in a low state, but this is completely the way it should work.

Pleased to hear that all is well. I use these for analogue sensing of visible and IR ambient light and have to attenuate the light levels reaching the sensors by physically stopping light with filters. In the switching mode such as meter readings, you are going from an off state (0-V output) to the fully saturated state (approx Vcc) with nothing in between. The IR version is as sensitive (almost) as the visible version, but will depend on the ambient levels of IR - bright sunlight and fluorescent fittings churn out high levels of IR. These are amazingly good devices with all the hard work of matching photodiodes to transimpedance amplifiers done for you. Don't be fooled by the black package.