I have been interested in adding a PAR sensor to my grow room. I have an Atlas RGB sensor in there now that measures lux, but it really only seems useful in determining if the lights are on or not, and doesn’t give me a lot of insight into how much the LEDs are driving photosynthesis. I’d really like to be tracking PAR, PPFD and DLI. I played around with a TCS34725 RGB sensor with different diffusers and now I think I am ready to spend a little $ on a reliable sensor.
I think I am going to go with a Quantum PAR sensor from Apogee Instruments. They offer sensors in SDI-12, Modbus, USB and analog 0-5v. Since I already have an ADC onboard, the analog 0-5V would be an easy plug-and-play option, but is more susceptible to interference/noise.
Has anyone used one of the Apogee Quantum PAR sensors with mycodo?
However, I’ve never had their communication cable to attempt to get measurements from the handheld meter to a computer. It’s listed at $100, which is too expensive, considering I’ve never had a need beyond the handheld use.
But looking at their comm cable page today, I noticed they offer a newer version they sell for half the price. It’s still very expensive for what is probably a <$1 FTDI chip inside, but I figured why not get one and I can let you all know how to make our own once I crack it open. I just ordered it.
This should allow me to get a working Input Module for Mycodo to read Apogee meters. I’ll give an update once I receive the part and can do some tests.
Cool! Yeah, that’s likely a good margin on those adapters-- thanks for biting the bullet on that! I went back and re-read the PAR discussion thread from a while back. I had looked at/tried some of those ideas (and the LEDGardener forum shut down that had some other DIY-PAR sensor concepts), and still think an Apogee quantum sensor will be my next upgrade-- but I’ll wait to hear your feedback. Thanks!
I have the Apogee DLI-600 meter. I also have one of their old-school USB cables as well somewhere…I did see their newer cable, which is USB-C which is neat. Would love to see what @KyleGabriel finds out about it =).
However, you can also get much cheaper PAR sensors from other places - they’re just not Apogee-brand.
DFrobot has a PAR sensor (SKU SEN0641) which works over Modbus:
Seeed studio also has one as well (SKU ) - I’m not sure why it’s a lot more expensive than the DFRobot one though:
Either way, both of those are a lot cheaper than the Apogee sensors - will be curious to see how they compare. I did pickup some cheap PAR Modbus sensors from Aliexpress before - haven’t had a chance to try them out though.
For reading Modbus - Waveshare make some pretty cheap Modbus-to-Ethernet (i.e. Modbus TCP, or to MQTT) devices.
Also, you’re going to get much better lengths using something like Modbus, than you would using USB - and the connectors are probably more robust (and IP-rated - which is likely better for a potentially damp/humid environment like a grow room).
I mentioned the USB variants because of the ease of use. Apogee even has a page that describes commands and example Python code to build your own software at Apogee USB Sensors and Linux. If I had to choose between the other output options, I would go with the 4-20 mA analog output.
I received the adapter and after removing the poured rubber shell, found it was simply an FTDI chip connected between the mini USB and USB-C. I’ll post photos and a wiring diagram later, once I reverse engineer the traces.
You don’t need an expensive PAR sensor to “track PAR, PPFD, and DLI”. There are now many phone apps that use the sensors in a phone to approximate what an actual expensive PAR sensor does, and calculate all of those things for you… and they are surprisingly accurate.
PPFD isn’t really something that you need to “track”… the PPFD from a quality light source isn’t going to change, you really only need to measure it once to gauge the distance you want your lights from the canopy to maximize light exposure and that’s it.
It took a little thinking to get it hooked up to mycodo. I used a 12-volt AC adapter (1amp) to power the sensor. I wired up the sensor power leads with a female barrel connector for the 12v input and a 3-pin M8 connector plugged in to a bulkhead in the Pi enclosure. That connector carries the sensor ground and signal (and one un-wired pin, there in case I change things around). I already had an ADS1115 wired up inside the enclosure monitoring a current clamp on A0, so it was easy to run the signal lead to the A1 channel and the high side of a 250 ohm resistor. The low side connects to the sensor ground and the ADC/Pi ground. That turns the 4-20ma signal into a 1-5V signal. The sensor’s calibration factor is 250 µmol/m²/s per mA so I have mycodo scale that channel to 0-4000 µmol/m²/s output. Now I have PAR being monitored, and the sensor seems quite accurate.
Nice score… it better be accurate, it’s a $500 industrial-grade sensor
Since you have the sensor working, it would be really interesting to see what the difference is between the $500 sensor and the free phone apps I posted just for comparison.
I received the Apogee adapter a while ago and removed the rubber case, but haven’t taken photos until now. Here are both sides and a close shot of the FTDI chip. The mini USB connects to the handheld meter and the USB-C connects to your PC.
