Using Apogee PAR Sensor and mVMeter - The Planted Tank Forum
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post #1 of 40 (permalink) Old 01-10-2017, 08:29 PM Thread Starter
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Using Apogee PAR Sensor and mVMeter

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.

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post #2 of 40 (permalink) Old 01-10-2017, 08:54 PM
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Try testing the mV meter alone to narrow down the possible problem. If you can link its part number or datasheet it might be easier to help.
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post #3 of 40 (permalink) Old 01-10-2017, 09:03 PM
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I'm look at the spec and it has 3 wires.

Green: Positive (signal from sensor)
White: Input power
Clear: Ground (for sensor signal and input power)

So you need to create a circuit for the signal to be read I assume.

White go to positive of the 9V, clear to negative of 9V. Positive lead of meter to green and ground lead of meter to negative of 9V.


I have the SQ-120 I use with a volt meter.


Last edited by mistergreen; 01-10-2017 at 09:09 PM. Reason: +
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post #4 of 40 (permalink) Old 01-10-2017, 10:14 PM Thread Starter
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Quote:
Originally Posted by mistergreen View Post
I'm look at the spec and it has 3 wires.

Green: Positive (signal from sensor)
White: Input power
Clear: Ground (for sensor signal and input power)

So you need to create a circuit for the signal to be read I assume.

White go to positive of the 9V, clear to negative of 9V. Positive lead of meter to green and ground lead of meter to negative of 9V.


I have the SQ-120 I use with a volt meter.
Yes, that's how it is hooked up, but the meter has 4 leads, red for battery +, black for battery -, green for signal +, and blue for signal -. I have the blue and black connected to the sensor ground (transparent), and the green to the sensor green.

I used my multimeter to try to measure the voltage across the green and blue wires, and got zero voltage. The 200 mV meter is: https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

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post #5 of 40 (permalink) Old 01-10-2017, 10:34 PM
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Can you draw out a quick diagram of how you have things hook up or a photo?

Try testing on a simple photo diode you have laying around. No need to supply the diode with power. It'll generate voltage when light strikes it.

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post #6 of 40 (permalink) Old 01-11-2017, 12:45 AM Thread Starter
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Testing the mV meter with a simple diode is a very good idea. I will do so shortly.

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post #7 of 40 (permalink) Old 01-11-2017, 02:00 AM
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AFAICT the output signal of the Apogee is 0-2.5V..
your box is 0- 200mV...
you can't measure (peg the circuit ) at more than 200PAR
1mV = 1PAR
https://www.google.com/url?sa=t&rct=..._HrV-g&cad=rja
All you need is a standard VOM w/ one probe on neg.. the other on signal..
At least that is how I see it..
OR a simple voltmeter gauge

Point of the powered sensor is the low level signal is amplified..

better...
https://www.amazon.com/bayite-wires-...voltmeter+0-30

Quote:
Wiring:
Red wire: Power supply +
Black wire:Power supply -, Measured Voltage -
White wire: Measured Voltage +


Link for meter PDF:
https://www.google.com/url?sa=t&rct=...QCsiMA&cad=rja

red/black power to the meter
green/blue what you want to measure..

My guess is you would need 2 power supplies..

"A man with a watch knows what time it is. A man with two watches is never sure."

Last edited by jeffkrol; 01-11-2017 at 02:30 AM. Reason: edit
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post #8 of 40 (permalink) Old 01-11-2017, 02:32 AM
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Quote:
Originally Posted by mistergreen View Post
Can you draw out a quick diagram of how you have things hook up or a photo?

Try testing on a simple photo diode you have laying around. No need to supply the diode with power. It'll generate voltage when light strikes it.
Still need to power the meter .. just connect the 9v to red/black..
diode goes blue/green

"A man with a watch knows what time it is. A man with two watches is never sure."
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post #9 of 40 (permalink) Old 01-11-2017, 03:17 AM Thread Starter
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Quote:
Originally Posted by jeffkrol View Post
Still need to power the meter .. just connect the 9v to red/black..
diode goes blue/green
Why wouldn't a single battery work? I have the diode in parallel with the meter power leads. That should be exactly the same as two separate batteries. The "ground" is not connected to any real ground, so it is just a common negative terminal. I realize I'm missing something, but what?

I haven't tried the simple diode yet, but may get to it tonight.

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post #10 of 40 (permalink) Old 01-11-2017, 03:26 AM
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You should be able to use one power supply. The apogee meter only has one power supply. It powers the meter and powers the sensor.


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post #11 of 40 (permalink) Old 01-11-2017, 03:33 AM
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Quote:
Originally Posted by mistergreen View Post
You should be able to use one power supply. The apogee meter only has one power supply. It powers the meter and powers the sensor.


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Different sensor...not amplified.. passive..well depending.. and who knows how the meter internal wiring works..

Bump:
Quote:
Originally Posted by Hoppy View Post
Why wouldn't a single battery work? I have the diode in parallel with the meter power leads. That should be exactly the same as two separate batteries. The "ground" is not connected to any real ground, so it is just a common negative terminal. I realize I'm missing something, but what?

I haven't tried the simple diode yet, but may get to it tonight.
From the spec sheet of the 4 wire device..
No no power supply needed for a diode.. it is self powered..so technically you have 2 power supplies..

If you stick the photodiode on blue/green and 9v on red/black it will work..or should if the signal is strong enough
As to your other sensor.. Different animal.. built in circuitry (amp) which needs power..
You meter looks to be "isolated" so to speak and again NOT enough range for over 200PAR..

Happy to be proven wrong.. but don't see it..

Depends on the sensor..


FIND what is wrong w/ the above vs the below:




(tired..)

"A man with a watch knows what time it is. A man with two watches is never sure."

Last edited by jeffkrol; 01-11-2017 at 04:03 AM. Reason: edit
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post #12 of 40 (permalink) Old 01-11-2017, 04:49 AM Thread Starter
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I hooked up a simple photodiode to the meter, and it worked fine. So, the problem is in how I'm using the powered sensor, but as far as I can understand, I am using it as it is designed to be used. Tomorrow I think I will disassemble all of my connections and do them again from scratch. I'm tired too!

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post #13 of 40 (permalink) Old 01-11-2017, 05:42 AM
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Are you using a bread board? Using a multimeter to check the circuit is helpful too.


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post #14 of 40 (permalink) Old 01-11-2017, 06:59 AM
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never mind
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post #15 of 40 (permalink) Old 01-11-2017, 05:48 PM Thread Starter
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It is a very simple circuit, so breadboard isn't needed. Here is the circuit:



And, I think I found my wiring mistake! As I recall, I had the two green wires connected. That wouldn't work at all. So, I will follow my plan and take it apart and rewire it.

It is back together again, and I'm 99% sure the connections are correct, but it now indicates -0.8 PAR at all times, no matter how much light it is sensing. Perhaps a solder joint isn't good, but I will wait awhile before checking it again.


Last edited by Hoppy; 01-11-2017 at 09:18 PM. Reason: add more information and pics
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