G+_Reggie Henneman Posted November 2, 2016 Share Posted November 2, 2016 on one of the grow how episodes it was sugested that supplementing grow lights for the sun would save on the electric bill, I have always wanted to dip my toe into circuit design and i was wondering if anyone could tell me weather or not this design would actually function keep in mind none that all components are placeholders only and are only for reference r2 sets the desired light level, t1 and r1 outputs the current light level via a voltage divider. both signals are inputted into an op-amp (ic1) configured to be a differential amplifier that output goes into the collector of t2 and also to another op-amp(ic2) configured to be a comparator just in case ic1 outputs negative voltage. Link to comment Share on other sites More sharing options...
G+_John Mink Posted November 2, 2016 Share Posted November 2, 2016 Just for my understanding, is this designed for a fixed amount of light or is R2 user adjustable? From the circuit diagram in reading R2 as controlled by T1 & IC1 but from your description it sounds more like a dial for the user. Apologies for my confusion.... Link to comment Share on other sites More sharing options...
G+_Eddie Foy Posted November 3, 2016 Share Posted November 3, 2016 I'd just use a plug in timer. Tweak it every couple of weeks for sunset/rise times. Link to comment Share on other sites More sharing options...
G+_John Mink Posted November 3, 2016 Share Posted November 3, 2016 If you want to to buy something, they do make these: http://www.instructables.com/id/Wiring-a-Dusk-to-Dawn-Photocell-Sensor/ But if you want to make it, don't let US stop you ;) Link to comment Share on other sites More sharing options...
G+_Reggie Henneman Posted November 3, 2016 Author Share Posted November 3, 2016 True i could just buy a timer and maybe i will end up doing that but my hobby is technology not buying things Link to comment Share on other sites More sharing options...
G+_Reggie Henneman Posted November 3, 2016 Author Share Posted November 3, 2016 John Mink you may be confused do to the fact that i tend to use the least amount of +5v and gnd symbols, r2 is a POT that receives power from one terminal and is grounded by the other terminal, the wiper outputs an analog signal that is adjustable for possible user tweaking. the voltage divider t1 and r1 output an analog signal to be compared with the output of r2. the purpose of the circuit is to identify how but light on a cloudy stormy or winter day were the amount of sunlight is not enough for an indoor grow and to add more through the use of grow light depending on how much a given plant(s) requires Link to comment Share on other sites More sharing options...
G+_Eddie Foy Posted November 3, 2016 Share Posted November 3, 2016 Keep in mind hobby self made stuff connected to the mains. Likely your homeowner's insurance won't cover it if it goes south in a bad way. Link to comment Share on other sites More sharing options...
G+_Jim Hofmann Posted November 4, 2016 Share Posted November 4, 2016 I agree, enough "Buy Now" sites out there. I like "Know How" :) But it has been awhile since I played with op amps. I found this describing basics. http://www.instructables.com/id/Op-Amp-Comparator-Voltage-Divider-Tutorial-With-/ I tried to evaluate your circuit. The photo sensor and R1 is a voltage divider, as light hits the sensor the reisitance drops and the voltage increases to the + input to op amp 1. R3 is used as a current limiter? Or maybe part of a feedback or latching circuit. The pot, R4 & R6 setup a second divider circuit. The pot is used to set the comparitive "fixed" voltage to the - input to the op amp. Not sure why R6 is on the op amp - input rather than on the pot output but it would still work. That's the easy stuff. SO, the output is 0V initially or when the light is low and +5V once the light is bright enough. R5 appears to be a feedback circuit. It appears to shift the input voltage once the op amp turns on. This means the photo sensor would need to see less light to turn off the op amp than if R5 were not there. IC2 and T2 confuse me. I assume T2 is meant to drive an output souce such as a 5 volt relay. However, the T2 collector is driven by the output of IC1 so why not just drive the relay from IC1? And what is IC2 for? The plot thickens. ;) Interesting, Jim instructables.com - Op-Amp Comparator & Voltage Divider Tutorial With Theory & Lab - Featuring The LM324 - All Link to comment Share on other sites More sharing options...
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