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Using Apogee PAR Sensor and mVMeter

14K views 101 replies 10 participants last post by  jeffkrol 
#1 ·
Has anyone tried to use a cheap digital mV meter and an Apogee SQ222, self powered sensor, to make a semi-DIY PAR meter? I received one of those sensors as a gift, and bought a cheap 200 mV digital meter to use as a readout. So far I haven't been able to make it work. I get a reading around 160 no matter if the sensor is illuminated or blacked out.

Using this version of the sensor requires supplying DC voltage to the sensor, and it gives a 1 mV per PAR unit readout (if it works). The sensor uses a common ground as the negative lead for both the supplied DC voltage and the DC mV output. The mV meter has 4 wires - two for the supplied voltage and two for the output voltage. I wired it with the common ground connected to both negative leads. Does that seem like the right way? I'm using a 9V battery for power, with the negative lead as the common ground.
 
#77 · (Edited)
I picked up a trim pot from Radio Shack, https://www.radioshack.com/products/radioshack-10k-ohm-15-turn-cermet-potentiometer-trimmer then measured the resistance the slider connection gives - it was roughly 50% of full resistance, so I hooked it up as shown in



I used a new 9 volt battery, and measured the voltage at the sensor - 5 volts! So, I tried it out..........................................IT WORKS!!

It gives a zero (actually a 0.1) reading with the cap on the sensor, and with the sensor about a foot from my little reading light, it shows about 20 PAR, which is what I would expect.

My conclusion is that this sensor, which is at least a couple of years old, was made to be used with 5 volts powering it, but later versions were improved so they can use 5-10, or whatever it is, volts.

Now, I need to try it in my tank to see how close it reads to what I am 90% sure is my PAR at the substrate. And, I will take some photos of it, inside and out, to post later.





 
#80 · (Edited)
The down side to using a resistor vs a v regulator is you'll have to use a fresh batter every so often. Say the battery goes down to 8V. The sensor would get less than 5V because of the pot. I'm not sure that would affect the PAR reading or not, but probably will.

I reread the sensor spec, it should stay operational at 2.5V-5V.
 
#86 ·


More good news. It works fine in a water filled aquarium, and the readings I got are very consistent with what I had a year ago, using a standard Apogee Quantum PAR meter (the original sensor type). I now have a acrylic pad attached to it to make it easy to use in an aquarium without your arm obstructing or reflecting light to introduce errors.

Now, I am figuring out details for making this available on loan to other members here. The really nice case I have for it won't fit into a small flat rate box or even a small flat rate padded envelope. So, I ordered a soft case from Amazon. That will fit the small flat rate box. Look for me to list this in the RAOK forum in a few days.

As usual with PAR meters once I made my measurements I may not want to use this for another 3 months, but it feels good to have one.
 
#90 ·
I have been thinking about this. That switch is very easy to turn on. One possibility would be a "cap" over the switch to protect it. Disconnecting the battery is the most reliable possibility, but can easily lead to a damaged battery connection. A piece of tape across the "off" end of the switch would work, but would quickly lead to a gummy, dirty area around the switch. Are there other options???

Incidentally, if the battery had not drained down I would still be stumped as to what the problem was.
 
#97 ·
I am sorry to revive this old thread, but I was wondering if one could provide a diagram how to use the passive version sq120 with raspberry pi. I have the MCP3008 analog to digital converter, but when i hook it up using the 3.3V I get the maximum voltage (3.3) as readout even in the dark. Obviously I should not power it from raspberry cause its passive? But still i cant make it work...Any ideas?
thank you !!
Stay Healthy!!
 
#98 ·
I am sorry to revive this old thread, but I was wondering if one could provide a diagram how to use the passive version sq120 with raspberry pi. I have the MCP3008 analog to digital converter, but when i hook it up using the 3.3V I get the maximum voltage (3.3) as readout even in the dark. Obviously I should not power it from raspberry cause its passive? But still i cant make it work...Any ideas?
thank you !!
Stay Healthy!!
SQ-120 is self powered..
Connect the sensor to a measurement device (meter, datalogger, controller) capable of measuring and displaying or recording a millivolt signal (an input measurement range of approximately 0-500 mV is required to cover the entire range of PPFDfrom the sun). In order to maximize measurement resolution and signal-to-noise ratio, the input range of the measurement device should closely match the output range of the quantum sensor. DO NOT connect the sensor to a power source. The sensor is self-powered and applying voltage will damage the sensor
https://electronicshobbyists.com/raspberry-pi-analog-sensing-mcp3008-raspberry-pi-interfacing/
https://pimylifeup.com/raspberry-pi-adc/


I can only "point " you but the Apogee outputs mA signal not voltage ..



not sure how you digitize 0-800mA...
 
#99 ·
Thanks Jeffkrol. I am aware that is self powered thats why i would like to know the diagram. All the sensors that they describe in the links (others as well) are with sensors that need external power source, or? This TMP36 for example, you counnect the VCC to the 3.3V of the raspberry. Do i miss something?
 
#100 · (Edited)
first you need to convert the mA to a voltage.. then go from there with the ADC converter (technically the easiest? though ??)

since raspberry pi has on analog input...
AFAICT..
https://forum.arduino.cc/index.php?topic=589808.0


https://www.rototron.info/raspberry-pi-analog-water-sensor-tutorial/


Waaay too many error points for my liking..

"As I understand it" you just need to find a suitable resistor across the 2 output wires of the sensor.
That's fed to the ADC to go to the Pi..

https://www.industrologic.com/aninput.htm

You'll have to calibrate the output to the orig specs i.e mA X 5 = y volts.
pg 11
https://www.apogeeinstruments.com/content/SQ-100-300-manual.pdf

Don't forget the immersion effect..
The SQ-100 and SQ-300 series sensors have an immersion effect correction factor of 1.08. This correction factor should be multiplied to measurements made underwater.
 
#101 · (Edited)
But I thought that the output of the sq120 is volt in the range 0-500mV.
If what you say is correct, using a 250 ohm resistor between the the two outputs of the sensor will give me a range of 0-5 Volts (according to your link), which is within the range and i can use the 3.3V of raspberry, right? Are you sure about this calibration? The outcome should be that the ADC should read now volt values in this region and then i have to calibrate mV*5=PPFD (manual pdf page 12, it doesnt say ampere, rather mV).
As you can see, its all new to me. Thanks again for your time!

I was unaware of this 4-20mA thingy...
 
#102 · (Edited)
But I thought that the output of the sq120 is volt in the range 0-500mV.
If what you say is correct, using a 250 ohm resistor between the the two outputs of the sensor will give me a range of 0-5 Volts (according to your link), which is within the range and i can use the 3.3V of raspberry, right? Are you sure about this calibration? The outcome should be that the ADC should read now volt values in this region and then i have to calibrate mV*5=PPFD (manual pdf page 12, it doesnt say ampere, rather mV).
As you can see, its all new to me. Thanks again for your time!

I was unaware of this 4-20mA thingy...

DANG, not sure where I made the wrong turn but yea..


Apogee SQ-100 and SQ-300 series quantum sensors are self-powered devices and output a voltage signal proportional to incident PPFD

Sorry, been a bit stressed out lately...
Technically the sensor part does output a mA or micro amp output but it's "converted" on the sensor head itself here..
It's best to use the mA output for a number of reasons BUT that is also a long story and not applicable here.


So IGNORE most of my prev. posts..and I have to see where I got lost..


you need to go sorting through this..
https://www.reef2reef.com/threads/r...troller-based-on-raspberry-pi.289256/page-279

Only difference between a pH probe and your sensor is calibrating output to ppfd.. instead pf pH..oh and no need to power the sensor (apogee) and you never have negative voltages..

https://raspberrypi.stackexchange.c...ion-and-adc-using-mcp3008-pcf8591-and-ads1115

Attach a BNC end to the 2 wires of the Apogee..
Then use this board..or one like it..
https://www.reef2reef.com/threads/reef-pi-ph-orp-adapter.478158/
https://github.com/reef-pi/pH-Board
SADLY unavailable..
https://www.tindie.com/products/ranthalion/isolated-ph-probe-interface-for-reef-pi/
Nuts and bolts using pH probe as an example.
https://www.atlas-scientific.com/_files/_datasheets/_oem/pH_oem_datasheet.pdf

THIS also should be helpful..
https://www.abelectronics.co.uk/p/69/adc-pi-raspberry-pi-analogue-to-digital-converter
https://www.abelectronics.co.uk/kb/article/27/analogue-to-digital-converter-buyers-guide
 
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