For a project, I am using a photo diode with 3 pins (Datasheet below): Vcc, Vout and ground.
I connected these to 5V, Analog1 and Ground respectively. Between the detector and ground is a 100kOhm resistor.
When i am measuring with the arduino Mega, or multimeter, i get odd voltages on the Vout-pin like 2.8 approx.
This should be near zero as the wavelength the diode is sensitive for is not present. When I turn on the UV-source the value does go up to 3.6 approx. This should be higher.
Is there anyone who can help me identify the problem? Is the detector wrongly wired or does the problem lie elsewhere?
The depends on the intensity of the light. Increase the value of the 100K resistor it is acting as a load for the photodiode which is needed. I use to use 74HC14 with a similar configuration, they worked great. The hysteresis of the part was a big help in getting ride of the noise. Simply connect the anode to+5, The cathode to a digital pin, and the resistor from the digital pin to ground. This will give you simple on and off signals. Use one of the analog pins if you want to measure the intensity.
Between the detector and ground is a 100kOhm resistor.
This is not mentioned in that rather sparse data sheet. What happens when you test without such a resistor ?
It is not, but what is mentioned is that supply current is typically 50 microA. I calculated the needed resistance to create that current with the 5V of the arduino. I dont want to force too high a current with the risk of breaking it. So i did not test without resistance. Or is it save without and is this what causes the voltage over the Vout pin?
EDIT:
I tested with 50K resistor and the voltage drops as is expected from a simple serie-resistor set-up.
So my question now is: is it safe to connected the detector without a resistor? Will the current dont go through the roof? My roughly calculated resistance of the detector (without relevant radiaton present) is 80k Ohm.
Thanks 6v6gt and gilshultz for making me look in the right direction!!
Firstly, I'm sure you have checked this already, but the pin out diagram shows the connections from ABOVE, not below the detector.
You MAY be able to confirm the connections as the GND pin would I assume connect to the metal case.
Secondly, the voltage range is specified as 5.5V DC MAX (no minimum indicated). You should probably have a decoupling capacitor across the supply pins at the device. And "just in case" I'd try running it from the 3.3V supply from the arduino.
If the supply has gone above 5.5V you MAY have destroyed the detector.
Thanks John for the advice, I will keep this in mind when I progress with my project. I will test what happens to the Voltage output when using the 3.3 and 5V pins and see which is best.
My take after looking at the datasheet:
When looking from the top, VCC is next to the small tab. The 100K wouldn't be needed ... it'll actually pull the voltage down a bit. The 50µA is just the current used to run the device, so the amplified output will be quite weak. I think direct connection of Vout to your analog input should work well. Taking double readings (discarding the first) may give more accurate results.
Indeed there was no extra resistor needed, for once I was being too carefull instead of too careless.
This changed the voltage on the V_out pin as you would expect.
I am using the 5V without any problems and have not found any reason to switch to 3.3V.
The project is now running as far as the sensors are concerned, on to the next step!
Hi,
Thanks for the reply, you can edit the thread subject and add [SOLVED], this will help with anyone else with a similar problem.
Hope your project goes well.
gilshultz:
The depends on the intensity of the light. Increase the value of the 100K resistor it is acting as a load for the photodiode which is needed. I use to use 74HC14 with a similar configuration, they worked great. The hysteresis of the part was a big help in getting ride of the noise. Simply connect the anode to+5, The cathode to a digital pin, and the resistor from the digital pin to ground. This will give you simple on and off signals. Use one of the analog pins if you want to measure the intensity.
Its not a bare photodiode, its a photo detector module with built in amplifier, the 100k on the output is unlikely
to have any effect if the output impedance is sane. Since the datasheet doesn't mention a resistor load,
best to remove it anyway.
The rogue output voltage with no UV illumination clearly indicates some sort of fault.
