Automated Yard Watering Project – InApps Technology 2022

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Making Connections

Ideally, we’d have a 10-pin 0.1 mm spaced connector to use to wire the relay board to the microcontroller. There wasn’t one handy so I modded the usual obsolete hard-drive cable connector down to 10 pins and soldered the wires into place. Just clamp the connector in a vise and cut the plastic connector with a small saw or Dremel abrasive disk. Here’s a close-up of the connector.

Hacked hard-drive cable connector used on relay board

I found it best to “touch” solder to both the pins and the ends of the wires before trying to join them. Old school hackers call this process “tinning.” The flux in the solder cleans the surface of the pin and makes the solder flow properly. The end of the wire is then positioned against the pin and soldered with a minimum of heat. Try to solder the pins as quickly as possible or the pins will melt the plastic in the connector and possibly short together.

For preliminary testing, I cut all the wires down to about two inches in length and used a small breadboard to connect to the NodeMCU board. Once I made sure the relay board worked, I removed the wires from the breadboard and soldered them to the top of the NodeMCU module pins. This operation is a little tricky since space is pretty tight between pins.

Wires soldered to the NodeMCU module

I prefer to use 22-gauge solid wire when working with breadboards and prototype projects. Stranded wire always separates when pushing it into a breadboard. Straight, solid wire ends go in very easily and minimize the chance of a shorted or open connection.

Finding good documentation for the eight-channel relay board is a bit sketchy on the web. I wasn’t sure if the board worked with 3.3-volt or 5.0-volt logic. Regular Arduino modules use 5.0-volt logic, while the Raspberry Pi and ESP8266 boards (NodeMCU) both use 3.3-volt logic. It turned out not to matter. I just hooked it up and gave it a try. Take a look at a generic internal schematic of the relay board.

I hooked the ground pin on the relay board up to a GND pin on the NodeMCU board. Likewise, the VCC pin on the relay board went to one of the 3.3-volt pins on the NodeMCU. Eight of the 13 digital GPIO pins are connected to the relay board for use and testing, so you can use the remainder for other purposes. There is also an analog input pin labeled A0, which we aren’t using at this time.

relay pin	NodeMCU GPIO	NodeMCU physical pin
N1	GPIO16	D0
N2	GPIO5	D1
N3	GPIO4	D2
N4	GPIO0	D3
N5	GPIO2	D4
N6	GPIO14	D5
N7	GPIO12	D6
N8	GPIO13	D7

Google has plenty of NodeMCU pinout images for your reference and entertainment.

Make sure the configuration jumper at the bottom right-hand side of the relay board (with the connector facing front center and the relays at the back) is positioned between the VCC and JDVcc pins. Ignore the adjacent Gnd pin. This setup should also work for the Raspberry Pi. You couldn’t ask for a cleaner or simpler layout of the NodeMCU and relay board. Connect the USB cable to a Linux notebook for the programming phase.

Upload the Test Firmware

The NodeMCU uses the Lua programming language and comes already loaded in the firmware. IBM has a little mini-intro for the NodeMCU that you might check out if you’re interested in their development kit and using Lua. I don’t have any experience with the language, so instead opted to write regular old Arduino code for this part of the project. Perhaps, we’ll investigate Lua in a future story, seeing as I have two other NodeMCU modules with which to experiment. It looks like it’s pretty easy to use.

Current versions of the Arduino IDE support the NodeMCU modules. I downloaded and installed version 1.8.7 on the ASUS Linux notebook. Be sure to select “ESPduino (ESP-13 module)” for the board type or the firmware upload will fail.

Next, I modded the example code for the ESP8266 blink program to basically blink the eight relays on the relay board. Here’s the code.

/* NodeMCU – relay board test program Sequentially turns each relay on and off for 2 seconds, loops forever */ // the setup function runs once when you press reset or power the board void setup() { pinMode(16, OUTPUT); pinMode(5, OUTPUT); pinMode(4, OUTPUT); pinMode(0, OUTPUT); pinMode(2, OUTPUT); pinMode(14, OUTPUT); pinMode(12, OUTPUT); pinMode(13, OUTPUT); digitalWrite(16, HIGH); digitalWrite(5, HIGH); digitalWrite(4, HIGH); digitalWrite(0, HIGH); digitalWrite(2, HIGH); digitalWrite(14, HIGH); digitalWrite(12, HIGH); digitalWrite(13, HIGH); } // the loop function runs over and over again forever void loop() { digitalWrite(16, LOW); // LOW lights optoisolator LED to ground – turns on relay delay(2000); // wait for a 2 seconds digitalWrite(16, HIGH); // HIGH kills optoisolator LED – turns OFF relay delay(2000); // wait for a 2 seconds digitalWrite(5, LOW); // LOW lights optoisolator LED to ground – turns on relay delay(2000); // wait for a 2 seconds digitalWrite(5, HIGH); // HIGH kills optoisolator LED – turns OFF relay delay(2000); // wait for a 2 seconds digitalWrite(4, LOW); // LOW lights optoisolator LED to ground – turns on relay delay(2000); // wait for a 2 seconds digitalWrite(4, HIGH); // HIGH kills optoisolator LED – turns OFF relay delay(2000); // wait for a 2 seconds digitalWrite(0, LOW); // LOW lights optoisolator LED to ground – turns on relay delay(2000); // wait for a 2 seconds digitalWrite(0, HIGH); // HIGH kills optoisolator LED – turns OFF relay delay(2000); // wait for a 2 seconds digitalWrite(2, LOW); // LOW lights optoisolator LED to ground – turns on relay delay(2000); // wait for a 2 seconds digitalWrite(2, HIGH); // HIGH kills optoisolator LED – turns OFF relay delay(2000); // wait for a 2 seconds digitalWrite(14, LOW); // LOW lights optoisolator LED to ground – turns on relay delay(2000); // wait for a 2 seconds digitalWrite(14, HIGH); // HIGH kills optoisolator LED – turns OFF relay delay(2000); // wait for a 2 seconds digitalWrite(12, LOW); // LOW lights optoisolator LED to ground – turns on relay delay(2000); // wait for a 2 seconds digitalWrite(12, HIGH); // HIGH kills optoisolator LED – turns OFF relay delay(2000); // wait for a 2 seconds digitalWrite(13, LOW); // LOW lights optoisolator LED to ground – turns on relay delay(2000); // wait for a 2 seconds digitalWrite(13, HIGH); // HIGH kills optoisolator LED – turns OFF relay delay(2000); // wait for a 2 seconds }

NodeMCU – relay board test program

Sequentially turns each relay on and off for 2 seconds, loops forever

// the setup function runs once when you press reset or power the board

void setup() {

pinMode(16, OUTPUT);

pinMode(5, OUTPUT);

pinMode(4, OUTPUT);

pinMode(0, OUTPUT);

pinMode(2, OUTPUT);

pinMode(14, OUTPUT);

pinMode(12, OUTPUT);

pinMode(13, OUTPUT);

digitalWrite(16, HIGH);

digitalWrite(5, HIGH);

digitalWrite(4, HIGH);

digitalWrite(0, HIGH);

digitalWrite(2, HIGH);

digitalWrite(14, HIGH);

digitalWrite(12, HIGH);

digitalWrite(13, HIGH);

}

// the loop function runs over and over again forever

void loop() {

digitalWrite(16, LOW); // LOW lights optoisolator LED to ground – turns on relay