Little Monster - Electrical Installation

The following details the steps to build the main electrical circuit which is located under the main hood of the mower and how to connect the other sensors and drivers in the mower.  Please follow carefully the instructions and you will create a step by step electrical circuit for the mower.   


if you consider yourself a beginner  at soldering please spend 5-10 minutes and watch a few soldering videos.  Its good time spent and will improve the quality and fun of your build

Video 1         Video 2




Step 1 - Arrange Components

Arrange the components as shown in the diagram below.  


Step 2 - Create a 5V Circuit

Solder a black wire (negative) and a red wire (positive) to the DC convertor on the IN side.  This will bring 12V power to the DC convertor.  The Dc Convertor is loctaed in the lower section of the mower. 

With 12V running to the Dc convertor turn the adjustment screw anticlockwise so that the 12V IN is converted into 5V out.  Use a voltmeter to measure the output voltage and adjust it to be 5V.

This 5V output will power most of the boards and sensors in the mower.  Make 2 sources for 5V out power.  1 in the lower section of the mower and 1 in the hood area in the location shown.  These 2 sources will lessen the amount of cable required to connect the sensors in the mower. 



Step 3 - Power to the MEGA

Using a separate positive and negative cable bring the 5V power to the Arduino MEGA.


Step 4 - Real Time Clock and NodeMCU

Connect the Real Time Clock and NodeMCU to the 5V power.  The positive and negative cables can be ran underneath the MEGA to keep the install looking as clean as possible.  Run the signal wires from the pins shown on the RTC and NodeMCU to the MEGA. 

NodeMCU D2 -> TX2 MEGA 

NodeMCU D3 -> RX2 MEGA

I really find it best to solder the wires as over time the Arduino wire pins can come loose.



Step 5 - Relay Connection

Again run 5V power to the relay and connect the signal pin to the MEGA.  The relay on the little monster is located in the lower section of the mower.  Try and keep all wires travelling from the upper hood to the lower section in 1 or 2 channels to the left and right of the hood.


Step 6 - Motor Bridge

The Motor Bridges do not require any 5V power supply.  Connect the signal wires to the MEGA as shown in the diagram below.






Step 7 - Volt Sensor

Connect the volt sensor to the 5V power supply and the signal pin to the Arduion Nano pin A1





Step 8 - Amp Sensor

Connect the amp sensor to the 5V power supply and the signal pin to the Arduion Nano pin A2



Step 9 - Nano

Connect the Arduino Nano to the 5V power supply and the serial communication pins to the Arduino MEGA.



Step 10 - Rain Sensor

Connect the rain sensor to A3 on the Nano and connect it to the 5V power in the lower section of the mower.


Step 11 - Compass Prep

The compass will run on 3.3V and requires a SCA SCL communication.  Prepare these wires for the compass.  The wires should be long enough to reach the compass module which will be located at the front of the mower.




Step 12 - TFT Touchscreen Preperation

The TFT Touchscreen is controlled by another Arduino MEGA board which it plugs into.  I will call this the 'TFT Controller MEGA'.  (The other which controls the mower movements I'll use the name 'Mower MEGA') 

Prepare the TFT Controller MEGA with:

5V power, RX1 and TX1 communication wires. 

Solder these wires to the TFT Controller MEGA before installing into the mower.  It is also best to upload the BMP data to the Micro SD card now and insert it into the touchscreen SD slot as it will be difficult to access later.

(If after uploading the code the touchscreen is not responding to touch, see the guide on the Arduino Software page on how to calibrate the screen)



Step 13 - TFT Connection

The TFT touchscreen communicates to the Mower MEGA via serial communication between the TFT Controller MEGA and the Mower MEGA.  connect the wires you prepared in Step 12:

TX3 Mower MEGA -> RX1 TFT Controller MEGA. 

RX3 Mower MEGA -> TX1 TFT Controller MEGA

Also connect the 5V and GND using the common 5V / GND power source.





Step 14 - 12V Switched Circuit via Relay

The 12V power for the wheel motors and the blade motor is switched on and off via the relay.  12V power comes into the relay circuit (COM) from the battery source. The 12V positive wire then exits the relay from the NO (normally open side), one power line to the wheel motor drivers and one power line to the blade motor controller. 

The negative 12V cable is connected to the GND side of the motor controller.  


Step 15 - Prepare Wheel Motor Lines 

Add 2 wires per wheel to the motor driver long enough to reach the wheel motors at the back of the mower.




Step 16 - Connect Sensors in the Lower Body of the Mower

The build should now look this and have the following wires available for connecting the other sensors/motors etc in the mower.  







Step 17 - Connect Compass Module

Connect the compass module to the pre-prepared 3.3V power, SCL and SCA wires.  The ground wire can be connected to the lower GND (5V area)






Step 18 - Wheel Motors

Connect the wheel motors to the pre-prepared wheel motor lines.  If the connector blocks are used the wheel motor wires can easily be switched to ensure forwards, backwards left and right are all working correctly. 


If the left motor turns instead of the right, exchange both motor wires on the motor with the other motor wires.  

If the correct motor turns, but in the wrong direction just swap the 2 wires that are already on the motor with each other.



Step 19 - Blade Motor Controller and Blade Motor

Connect the pre-prepared 12V supply comign from the relay to the blade motor controller as shown in the diagram.  Then connect the 12V GND wire to the GND connection point on the 12V circuit.




Step 20 - Blade Motor Controller Communications

Now connect the blade controller to the Arduino MEGA main board so the blade motor controller can be controlled by the Ardunio MEGA..

3 communication wires go to the Arduino MEGA.  The VCC and GND wires are connected to the lower 5V output point.






Step 21 - Sonar Sensor

The sonar module is now connected.  The sonar module requires a 5V+ GND Trig and Echo wire.  The 5V circuit can be connected to the lower 5V output point.  The Echo and Trig wires are connected to the Arduino MEGA on pins 36 and 37 as shown below.




Step 22 - Wire Sensor

The wire sensor is prepared as shown in the following diagram.  The capacitor on the 200x Audio Amp shoudl be bridged by soldering the 2 pins on the lower side of the board.


The wire sensor is then connected to the circuit using again the 5V lower output as shown below.  The signal wire is connected the the Arduino MEGA pin A5.


Step 23 - Switch and Battery

The main 12V LiIon battery is connected to the 12V circuit as shown below.  The main power switch cuts power to all components once turned off.  A positive lead from the 12V circuit is ran to the volt sensor to measure the mowers battery voltage.




Step 24 - Charge Plugs & Amp Sensor

The battery needs to be charged even when the main switch is off.  For this reason the charge cables are ran to the battery plug before the main power switch.  The positive lead of the charge cable is ran through the amp sensor to measure when a charge is present.




Step 25 - Tip and Tilt Sensors

Prepare the sensors and fix them into the 3D printed plate.  Ensure that the sensor head of the tip sensor is bent by 90°




Connect them to the circuit as shown below.



Step 26 - Bumper Microswitches

The Front bumper microswitches are loctaed at the front facia of the mower.  They require a GND and a COM wire per microswitch.  (no 5V+ supply is required)




That completes the full electrical install.  All the components can be tested using the test function in the TFT display.