Melon Green is a controller board which is useful to operate any electronically switchable (On/Off) agricultural facilities. You can put it through a variety of setups. This sample setup schematic, shows how to use most of M.G's potentials in a greenhouse:
The older Melon Green v1.0.0 uses a common power path to relays and main electronic parts (including AVR Microcontroller through a 7805 regulator). Because an AVR can tolerate currents less than ~500mA (~50mA for IO pins), sometimes it's wise to separate power sources for relays. In such cases, please use newer versions which have some jumpers to switch between Int/Ext power source for relays.
- J0 is the power source inlet. 7-12 V DC is OK. An AC to DC adapter is needed for normal house outlets. A Nine-volt heavy-duty battery works too.
- J10 & J11 are jumpers which switch the Internal/External current to relays. J10 for negative terminal (Ground) and J11 for positive terminal (Vcc).
Note! Change both of them together. - J12 is the power inlet for the relays, if an external power source is available.
All sensors are optional.
Each sensor helps M.G. to control actions (like Irrigation) based on the related Environmental Variables. If you take a look at the board, you'll find titled sensor terminals (like: J# - Sensor) on the left side of the board. Each Sensor terminal has three pins: (from Left to right) Vcc [~5v] Gnd [Ground] & Data.
Note!
1. Remember to [Customize Melon Green's Code](2. Upload the Melon Green to AVR.md) for the sensors being used.
2. Calibrate Sensors via [Serial CLI](3. Serial Command Line Interface.md) for accurate results.
Allowable Voltage/Current for each I/O pin is ~5v/45ma
One of the most useful parts is a Digital Humidity & Temperature Sensor. DHTxx Family Sensors are cheap and handy. M.G. is compatible with DHT22 (AM2302), DHT21 (--Not Tested) & DHT11 (AM2301) by default. You can directly connect DHTxx to Standalone MG because the board has built-in Pull-up resistor. No need for modules or breakouts.
Four legs are: Vcc (~5v), Data (i/o), Nc (Not connected) & Gnd (-).
| DHTxx | Measurement Range | Humidity Accuracy | Temperature Accuracy | Sampling rate |
|---|---|---|---|---|
| DHT 11 | 20 |
5% | 2° | 1Hz |
| DHT 22 | 0 |
2~5% | 0.5° | 0.5Hz |
Analog Soil Moisture Sensors generally sense the conductivity of the soil. As moist the soil is, less electrical resistance will be there.
Feeding Solution Mixer (Please see below for details) is a useful experimental tool which helps user to mix water & thick liquid fertilizer in a third [Food] tank. If water is used directly (no fertilizer added, so no need for food mixing), you don't need this sensor.
M.G. uses an analog terminal to measure how much food is in the tank. Food level threshold calibration (Min & Max) is possible via serial CLI. Settings for fertilizer/water ratio and food tank volume are in Feeding Solution sub-menu.
Rain Detector which we use, is a simple digital on/off sensor. It passes ~5v from the Vcc Pin to the Rain Data Pin when it's rainy out there [ ~ e.g. Rain Drops Make a Short Circuit ] or ~0v when it's sunny. DIY & don't worry about pull-down, it's built-in to prevent false senses.
Commercial sensors are available out there as well.
You can use any Analog Light Intensity Sensor (Less than 5v output) or a LDR (Photocell). If you would rather use LDR, connect each leg to one of the Vcc or Data pins (Normall LDRs are not polarized). The built-in variable pull-down resistor (trimpot - R1) is useful to change the LDR's sensitivity to darkness and/or lightness. Here is an interesting article about Using a Photocell with pull-down by Lady Ada.
There are many Irrigation Systems or Growth Environments in the real word, like Hydroponics or Drip Irrigation. Some of them need grow light supply and some have heaters or foggers/humidifiers. Melon Green is a controller, so you may use it in any system with customization.
In fact, when it's time to turn solenoid valves open or water pumps on for irrigation (according to settings), or when it's time to turn heater on, AVR makes dedicated SPDT relay HIGH/Active and relay connects COM (far right pole/leg/screw of the terminal) to NO (Normally Open - far left leg/throw of same terminal). The middle leg is NC (Normally Closed throw - It's connected when the relay is inactive.
e.g. Home Drip Irrigation System
For Example, this figure shows how to setup most simple M.G. powered drip irrigation in home:
This setup probably uses time-based functionalities of your M.G.
Sometimes it's necessary to feed plants with mixed water and fertilizer (or other treatments like sanitizers) on a regular base. In such cases M.G. has an experimental functionality to dilute concentrated liquid (= Generally mixing two sources).
