Hi,
I recently purchase a quantum light meter from Walz (LS-C Mini Quantum Sensor | WALZ), Germany and I am trying to read the value using an arduino Uno but so far I can't find any shield or way to read the sensor. I might need a BNC board or shield but I am not sure where to find one. Any thoughts?
The data sheet says the typical output is 10 uA, so you will probably need a high value resistor to change the current to a voltage and some amplification. I would ask the company for a typical application (i.e., what kind of load resistor is appropriate), since I see no mention of output impedance.
Ok let me check with them and get back to you. But already, do you know if there is some kind of connector I can use to connect to my arduino?
do you know if there is some kind of connector I can use to connect to my arduino?
At the end of the day a connector is just wires. Where they get interesting is when the impedance presented to the source has to match the impedance of the connector.
This is only important at high frequencies, much higher than an arduino can cope with, so there is little point in trying to get a fancy connector on an arduino.
Just buy a BNC connector of the opposite sex and solder (short!) wires to it.
Assuming the sensor comes with a BNC cable and plug attached, just get a BNC socket like this one http://www.maplin.co.uk/insulated-bnc-chassis-socket-1570.
The best way of interfacing it to an Arduino depends on whether it is intended to be used in forward or reverse biased mode, and what its polarity is (i.e whether the cathode or anode is connected to the BNC cable shield). Unfortunately, the web page for the sensor doesn't specify either of those. If it is intended to be used in reverse biased mode, you also need to know the maximum and/or recommended reverse bias voltage. I suggest you ask the manufacturer for this information.
This is what I get from them:
"Be aware that the light sensors produce usually negative current (in other words: cathode is inside, anode is outside; or: plus and minus are the other way round than what you usually expect)... if you connect it to a usual very sensitive ampere meter, it shows negative numbers", is it what you were talking about dc42.
Should I expect Arduino to be sensitive enough?
I think you should use an op amp to amplify the signal and invert its polarity. Half a LM358 will probably do, although something like OPA320 would be better. Connect it like this:
Negative supply to ground
Positive supply to +5V
Non-inverting input to ground
Inverting input to sensor output, also connect a 100k resistor between inverting input and output
If using lm358, also connect a 1k pulldown resistor between output and ground
KeithRB:
The data sheet says the typical output is 10 uA, so you will probably need a high value resistor to change the current to a voltage and some amplification. I would ask the company for a typical application (i.e., what kind of load resistor is appropriate), since I see no mention of output impedance.
No, don't use a high value resistor. This is a PV cell, and the current output depends on the voltage
so you'll have to clamp the voltage (presumably at 0V) to measure it. A current->voltage converter
using a simple op-amp circuit is probably all that's needed.
However we don't know the polarity of the current!
If lucky then the centre conductor is negative and this simple circuit will do
Where the opamp is rail-to-rail, R sets the volts-per-amp of course!
Actually in a sense this is a high value resistor, its just decoupled from the voltage at the
sensor since the sensor output is virtual ground. As other(s) mentioned this sensor might
need a particular level of reverse
bias to get nominal performance...