I am new to designing circuits but I have spent a lot of time researching for this project. I have been designing an automated indoor garden for my home. To save space, there will be 3 gardens stacked vertically. The gardens will be self watering using moisture sensors, a pump and solenoid valves. It will also have blue and red LEDs to provide light to the plants.

Here is the link to a google doc of my project for more details: https://docs.google.com/document/d/1jLP35pS16meeRFSbU6V1jtvDDfdHTNM6jPjyyabYSCg/edit?usp=sharing

I have made my circuit using an electronic circuit simulator I found online. Here is the link to it:


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As you can see, I am using 1 pump, 3 solenoid valves (indicated by the green light), 15 blue LEDs, 27 red LEDs, and a laptop charger as the power supply(20V, 4.5A). To control the pump and valves, I am using transistors and an Arduino UNO.

The idea is that the moisture sensors will detect when each level of the garden needs to be watered. When a level of the garden is too dry, the Arduino will send power to the pump to turn it on. The Arduino will also send power to a specific valve to allow water to flow to that level of the garden.

Component Data:





So the question is, can anyone see any problems with the circuit before I actually build it? I am pretty new to electronics so I am worried I am going to damage some of my components.

A more specific question I had was, am I representing my pump correctly in the simulation? I have used a resistor to represent it. Should I be using a diode like I did for my valves?

Please let me know if I need to provide more information. Any feed back I receive will be greatly appreciated! :)


Thank you for all your wonderful suggestions! :) I have used your suggestions to change a few things. I am splitting the watering and lighting portions up into 2 separate circuits, each with their own power source. The watering side will be using a 12V power source, while the LEDs will have a 20V power source. Using separate power supplies also gives me the option to add additional levels to my garden in the future since I no longer have to worry about going over my power supply current rating.

Here is the link to the updated simulation of the watering circuit

I am going to wait until my LEDs arrive in the mail before I design my circuit for them. Since they are from china, I want to test them to see what their specifications actually are. I am also looking into current regulators for them.

  • \$\begingroup\$ Can you add a proper circuit diagram and one that doesn't have moving symbols all over it. Naming components and providing data sheet links to components is also highly recommended if you want decent answers. \$\endgroup\$
    – Andy aka
    Mar 5, 2017 at 20:02
  • \$\begingroup\$ Next time, check out how to insert links and insert images as well. \$\endgroup\$
    – JRE
    Mar 5, 2017 at 20:03
  • \$\begingroup\$ You need resistors in the base leads of the transistors - 1K or so may do. \$\endgroup\$ Mar 5, 2017 at 20:46

1 Answer 1

  1. Simulating the pump: A resistor is not a bad way to model the pump in this case since it will just be on or off. More accurately it would be modeled as an inductor with series resistance, but I wouldn't bother in this case. Mind you I'm not sure how much value there is in simulating any of this circuit as it's fairly straightforward to calculate current draw and voltages. It's actually more accurate to model the valve as a resistor also instead of the diode.

  2. Why did you put the 50 and 7 Ohm resistors on the emitter side of the transistors? You should put those on the collector side to make sure the transistors saturate when turned on. The series resistor would 100 Ohms for the pump ((20-12)/0.08) and it looks like you split it into 50 on top and 50 on bottom. I don't see why. You did something similar for the valves, but here you added 1 Ohm and 7 Ohms for some reason. I think because the valve is modeled as a diode which adds voltage drop. Just do that the same ways as the pump, and again put the resistance in the top side. It would be much better if you could use a 12V supply so you can drive the pump and valves directly, rather than using series resistors which will get hot and waste power. That would require more LED chains, but that should not be a big problem.

  3. The transistors need resistors at the base terminal as Peter mentioned.
  4. You should include flyback diodes on the valves and pump to avoid damaging the transistors.
  5. The LEDs: Assuming you stay with 20V, the 7 Ohm resistor for the Blue chains is probably OK, but I think the 1.3 Ohm resistor for the Red ones is probably too small. It's hard to accurately simulate LEDs like this. I would start with a higher value resistor and measure the current before reducing the resistor value. Otherwise you might overdrive your LEDs and possibly damage them. If you use a lower voltage supply, you would need to reduce the number of LEDs and recalculate the resistors, but again, start with higher values until you get actual readings. Ideally you should use constant current LED drivers, but if you use the resistors, make sure they are rated for the power they will dissipate. This is a pretty cool LED array designer that might help.
  • \$\begingroup\$ Note that the red LEDs, if their voltage is 2 volts rather than 2.2, will draw 1.5 amps per string, while if the blues are 3 rather than 3.4 they will draw 0.7 amps per string. and the power supply will to into current limit. \$\endgroup\$ Mar 6, 2017 at 5:54
  • \$\begingroup\$ Thank you for all the great suggestions! I really appreciate it! I have taken your advice and updated the parts for the motor and valves. I still need to do some research to figure out how to add your suggestion for flyback diodes on the valves and pump. Here is the link to my updated design [Split comments up into 2 parts due to char restrictions] \$\endgroup\$
    – c1eave
    Mar 8, 2017 at 19:17
  • \$\begingroup\$ The calculation you showed me to find the resistor value for the pump worked really well. However, when I tried to do the same from the valves, it didn't seem to work out. I did (20-12)/0.6 = 13.3ohms. When I add a 13 ohm resistor to the circuit, my current is only 427mA when it should be 600mA and the voltage drop is only 8.55V when it should be 12V. I am not sure why. Does it have to do with the value of the resistor before my transistor? How do I figure out what value my resistor should be before my transistor? \$\endgroup\$
    – c1eave
    Mar 8, 2017 at 19:17
  • \$\begingroup\$ You should measure the voltage drop across the transistor (collector to emitter). It should only be about 0.2V. If it's higher then it's not saturated and it will be dissipating more heat than it needs to. You said "Does it have to do with the value of the resistor before my transistor?" Do you still have two resistors, or only one now above the transistor? \$\endgroup\$
    – AngeloQ
    Mar 9, 2017 at 2:16
  • \$\begingroup\$ I had only one resistor on the base side of the transistor (1k ohm). The voltage drop across the transistor (collector to emitter) was 6V. I changed the resistor from 1k ohm to 100 ohm and the Vce is now 56mV. That also fixed my problem in my second comment. The 13 ohm resistor in series with 20 ohm resistor(the valve) now gives me the correct current can voltage drop. Thank a lot! \$\endgroup\$
    – c1eave
    Mar 9, 2017 at 13:15

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