PCB 1.2 (English)

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Pcb top.jpg

This page describes how to assemble the Ardumower PCB and how to add the modules.

Required parts for the Ardumower

Overview

All modules can be purchased as complete kits via the shop Shopping.png .

What is needed for building your Ardumower:

Abstract

The controller is built around a ready microcontroller board (Arduino Mega 2560 using 54 I/O pins).

Needed modules

All modules can be purchased as complete kits via the shop Shopping.png .

PCB

The printed circuit board (PCB) connects all electronic modules. The PCB is made with the following design parameters:

  • PCB dimensions 241x114mm
  • All modules (motor driver, Bluetooth, etc.) can be soldered (or plugged) on the PCB (modules are available in the Ardumower shop)
  • Uses the Arduino Mega 2560
  • Optional: can use Arduino Due via additional adapter PCB
  • Optional: integrated charging circuit (current limiting)
  • All connections are available on connectors as well as +5V and GND
  • Max. trace current (for motors): 8A

PCB building manual

Robot PCB v0.5 (initial prototype, please do not use anymore)

Robot PCB v1.2 (minor layout changes)


NOTE: The schematics and PCB files were created with KiCad. They can be downloaded from github and can be edited by open source KiCAD software (Download here or here).

PCB building videos

PCB jumpers

Feature used YES NO Comment
Integrated charging control via adjustable

voltage regulator (LM350T) with potentiometer

for adjustable charging voltage (recommended: NO)

D7: DIODE

D3: DIODE

C1, C4, U4, RV1: used

D7: SHORT-CIRCUIT

D3: SHORT-CIRCUIT

C1, C4, U4, RV1: not used

Do not use if using external battery charger
External power while charging (recommended: NO) JP6: CLOSE

JP7: OPEN

D4: DIODE

C5: not used

JP6: OPEN

JP7: CLOSE

D4: SHORT-CIRCUIT

C5: used

Use to power your PCB from externally (disconnect battery from PCB) while charging
Arduino controlled charge relay (recommended: YES) JP4: CLOSE

JP5: OPEN

JP4: OPEN

JP5: CLOSE

Use for Arduino controlled charge relay (not automatic charging)
Arduino Due (3.3V I/O) LP0, ..., LP15: OPEN LP0, ..., LP15: CLOSE Do not use if using Arduino Mega
Bluetooth VCC=3.3V JP8: OPEN

JP9: CLOSE

JP8: CLOSE

JP9: OPEN

Many latest modules use 3.3V
Bluetooth programming mode JP2: CLOSE JP2: OPEN Use for reprogramming baud rate etc.

PCB modules

Note for Marotronics INA169: Short pads for 5A operation
Module Feature Pinout Optional Comment
U1 DC/DC converter (10V) GND, Vout, Vin, GND No
U2 Bluetooth (HC-05) VCC, GND, TXD, RXD, Key, LED Yes
U3 Current sensor (charging) VCC, GND, OUT, IP+, IP-5 Yes
U4 Charge control (LM350T) AJD, OUT, IN Yes
U5 Current sensor (charging) VCC, GND, OUT, IP+, IP-5 Yes
U6 DC/DC converter (3.3V) GND, Vout, Vin, GND No
U7 DC/DC converter (5V) GND, Vout, Vin, GND No
U8 Realtime clock (DS1307) Batt, GND, VCC, SDA, SCL, DS, SQ Yes
U9 Wifi (ESP8266) TX, CH_PD, Reset, VCC, GND, GP_IO2, GP_IO0, RX Yes
U10 Level shifter 5V->3V (Arduino Due) Yes
U11 Wifi (ESP8266) TX, CH_PD, Reset, VCC, GND, GP_IO2, GP_IO0, RX Yes alternative mount position

PCB connectors

Connector Feature Pinout Optional Comment
P1 Sonar center (HC SR-04) 5V, GND, Trigger, Echo Yes
P2 Sonar right (HC SR-04) 5V, GND, Trigger, Echo Yes
P3 Sonar left (HC SR-04) 5V, GND, Trigger, Echo Yes
P4 reserved Yes
P5 IMU (gyro,acceleration,compass) (GY-80) Yes
P6 Lawn sensor Yes
P7 Status LEDs Yes
P8 Odometry right Yes
P9 Odometry left Yes
P10 GPS (GY-NEO6MV2) Yes
P11 Bumper GND, GND, right, left Yes
P12 Perimeter coil (center or left) 5V, GND, perimeter Yes
P13 R/C remote control 5V, GND, mow, steer, speed, switch Yes
P14 Measurement points 5V, GND, (Depending on JP15: 3.3V, 5V or Arduino 3.3V) Yes
P15 Wheel motor left M1OUT1, M1OUT2 No
P16 Optional motor driver input Yes Do not connect
P17 Optional motor driver input Yes Do not connect
P18 Wheel motor right M2OUT1, M2OUT2 No
P19 Tilt sensor 5V, GND, tilt Yes
P20 Button (Start/Stop) No
P21 Drop sensor right Yes
P22 Reserved Yes
P23 Reserved Yes
P24 Reserved Yes
P25 Reserved Yes
P26 Reserved Yes
P27 Reserved Yes
P28 Reserved Yes
P29 Reserved Yes
P30 Perimeter coil right Yes
P31 Drop sensor left Yes
P32 GND Yes
P33 5V Yes
P34 3.3V Yes
P35 Mower motor RPM Yes
P36 Reserved Yes
P37 Mower motor No
P38 Reserved Yes
P39 Reserved Yes
P40 User switches Yes
P41 Rain sensor Yes
P42 Charging pins Yes
P43 Battery (24V) No
P44 Wifi module (ESP8266) Yes
P45 Reserved Yes
P46 Reserved Yes

Power supply

Please also read the section 'Voltages' under Motor driver for more information on motor voltages.

It is recommended to use a voltage step-down converter (e.g. module using LM2596) to generate the 5V voltage for the Arduino and all additional modules. Before connecting, set the voltage of the converter to 5V.

Warning.pngWarning : never connect more than 5V on the Arduino 5V pins, or you will damage the Arduino. Therefore, always measure the 5V voltage before connecting it to the Arduino 5V pin! All components together (as shown in the schematics) need about 5W power.


Motors

Ardumower uses two different types of motors (all motors can be purchased via the shop Shopping.png):

  • Two motors (with integrated gearing) for driving (wheel motors) and with integrated encoders (for distance and speed control)
  • One motor (with high rotation speed) for mowing (mower motor)

To control the motors, it requires motor drivers. In addition, the motor driver measures the motor current, and allows us to detect obstacles as motor current increases at obstacles. Ardumower uses two dual MC33926 motor drivers, so two channels for left and right motor and two dual channels (connected in parallel) for the mowing motor.

It is not safe to connect motors directly to the motor driver. Especially, when quickly turning motors from forward to reverse (or vice verse), high voltage spikes appear, and these could damage the motor drivers in the long run. Therefore, we developed driver protector boards that are connected between motor driver and motor.

Ardumower motordriver overview.png

Voltages

As in all modern systems, Ardumower uses 24V motors.

Motor driver assembly (dual MC33926)

Motor driver features: up to 3A with integrated current sensor and thermal shut-down protection

For wiring of motor drivers, protector and motors, please open manual in section Protector PCB.

Protector PCB

Warning.png When quickly tunring motors from forward to backward (or vice versa), high voltage spikes appear. These high voltage spikes could damage the motor driver in the long run. To eliminate high voltage spikes, it is adviced to use a Protector board between motor driver and motor. Two Protector PCBs are required, one for the gear motors, and one for the mowing motor.

Wheel motors wiring

The two left and right gear motors are controlled independently (aka 'differential driving') to:

  • drive the robot forward/backward
  • steer the robot left/right

Wheel motor features:

  • A rotation speed up to 31 rpm allows to move the robot at sufficient speed (at up to meter/sec = 31rpm/60 * PI * 0.25m = 0.4m/sec using 250mm diameter wheels)
  • A high torque (2.45Nm) guarantees that the robot can climb small hills as well (with 2 motors, 0.125 radius wheel, 31rpm = 0.4m/s, acceleration = 0.2 ( 1/2 of nominal speed) see calculator
  • Integrated encoders, so it can measure the rotation speed and the distance
  • 24V (load current ~1A)

The left gear motor is connected as follows to the protector board:

Motor wiring (left motor):

Motor (black)  ==== Protector board Motor_1_OUT(1)
Motor (red)    ==== Protector board Motor_1_OUT(2)

For right motor, use Protector board Motor_2_OUT(1,2) accordingly.

Wheel motors odometry wiring

The Ardumower gear motors have integrated encoders. These encoders help us to compute speed and traveled distance. Here's how you connect the motor odometry wires to the PCB.

Motor odometry wiring (left motor):

Motor (brown)  ---- PCB VCC
Motor (green)  ---- PCB GND
Motor (blue)   ---- PCB OdometryLeft (3)
Motor (purple) ---- PCB OdometryLeft (4)

For right motor, use PCB OdometryRight accordingly.

IMPORTANT: PCB v0.5/1.2 are missing pull-up resistors! You need to add them yourself at the PCB:

PCB OdometryLeft(3) --- 4.7k --- 5v
PCB OdometryLeft(4) --- 4.7k --- 5v

Mower motor wiring

The Ardumower mower motor features:

  • Fast enough to cut the lawn (3150 rpm)
  • Enough torque (140 mNm / 46 W)
  • Quiet mowing (you cannot hear it)
  • 24V, load current ~1.0A (L=2.8mH, R=1.9ohm)

Warning.pngSecurity note: For security reasons, always remove mower blades in your first tests!


Here's how you connect the mowing motor to the protector board:

Motor (black)  ==== Protector board Motor_1_OUT(1)
Motor (red)    ==== Protector board Motor_1_OUT(2)

Motor decrease noise

Here's how you can decrease motor noise:


Charger

For the charger, we are using a Lithium Ion e-bike charger (29.4V, 1.5A current limitting) that can be purchased via the shop Shopping.png. The charger is placed in a protected area (house etc.) and connected to the robot charging station. The charger should accomplish the following things (in this case Lithium-Ion, lead battery is similar, but less critical):

  • Charge battery pack via the charging pins of the robot
  • Maximum cutoff voltage / charge voltage compliance (charging voltage limit)
  • Maximum charging current compliance (charging current limit)

If you are using an existing charger, these things are implemented with high probability already in it. If you don't want to use a charging station, the charger can be connected directly to the Ardumower.

Total power balance

  • 2 x Gear motors each 1A (under heavy load): 2A, 27 volt (measured at max. 80% accuracy by motor drivers)
  • 1 x Mower motor 1A (under normal load): 1A, 27 volt (measured at max. 80% accuracy by motor drivers)
  • PCB: 1A, 5 volt (not measured by PCB)


Total: 3A * 27v + 1A * 5v = 81W + 5W = 86W

Battery

Sony Konion 7S2P battery pack (29.4V, 4500 mAh)

For the battery, we are using a 'Sony Konion 7S2P' Lithium Ion battery pack (Sony Konion US18650V3 2250 mAh cells, Li-Mn), 29.4V x 4500 mAh = 132 Wh, 500 recharge cycles, 126 x 36 x 65 mm (LBH).

Using this battery with the Ardumower motors, the mowing time is about 1.5 hours (132 Wh / 86W).

battery charge/discharge conditions for optimal battery life time:

  • charging per cell: max 4.15v (0.3A - 0.1A charging cutt-off)
  • discharging per cell: min 3.1v

Here you can see the charging without charging station. If you don't want to use a charging station (or for your first tests), the charger can be connected directly to the Ardumower:

Ardumower battery overview.jpg

Standby-off / Under-voltage protection

You can add an undervoltage protection to your Ardumower. There are two reasons for a battery switch (standby-off mechanism):

Reason1: If the robot was not started within 5 minutes, it should turn battery off to save energy.

Reason2: Modern batteries should not be completely discharged. When the robot isn't able to charge for some reason and when the battery is below a certain threshold, it should be able to switch off the battery itself (undervoltage protection)

schematics

Videos

  1. Driving into charging station
  2. Drive in and out
  3. Tracking and docking
  4. Final version

Bluetooth module

On the robot, you'll need a Bluetooth HC-05 module supporting Bluetooth Serial Port Profile (SPP). SPP uses Bluetooth Service Discovery Protocol (SDP) and the RFCOMM protocol.

Bluetooth HC-05

Wiring:

Bluetooth HC05 VCC --- PCB VCC
Bluetooth HC05 GND --- PCB GND
Bluetooth HC05 TX  --- PCB RX 
Bluetooth HC05 RX  --- PCB TX

For Programming the Module, you must connect the Key Pin from the BT Module to the 3.3 V from the PCB and disconnect after programming.

Ultrasonic Sensor

Ultrasonic.jpg

An ultrasonic sensor (HC-SR04) allows Ardumower to detect obstacles.

Distance 2 to 450 cm

Wiring

Ultrasonic Module VCC (+5V)  — PCB VCC (+5V)
Ultrasonic Module GND        — PCB GND
Ultrasonic Module Trigger    — PCB Digital Pin
Ultrasonic Module Echo       — PCB Digital Pin

An internal schematics of the sensor can be found here.[1]

Rain sensor

Using a rain sensor, your Ardumower can stop mowing when it starts to rain. Additionally, it can drive into your charging station.

NOTE: If using YL-83 module, we have no long-term experience regarding corrosion!

Wiring

                    GND o-----o GND Rain sensor module 
                    +5V o-----o VCC Rain sensor module           
      Ardumower pinRain o-----o D0  Rain sensor module
                                    Rain sensor module IN o----- rain sensor
                                    Rain sensor module IN o----- rain sensor

Photos

Videos

  1. Rain sensor test
  2. Simulated rain

Further links

  1. Principle schematics
  2. Rain sensor example

GPS

With the help of a GPS receiver (e.g. GY-NEO6MV2, ublox 6m), the long-term position can be calculated. Therefore, the GPS position values will be averaged.

Currently, GPS is used

  • to receive current date and time

Wiring:

GPS VCC -- PCB VCC
GPS GND -- PCB GND
GPS TX  -- PCB GPS RX
GPS RX  -- PCB GPS TX

Model R/C

The Ardumower can be controlled via a model R/C. For remote controlling your robot mower you'll need:

  • a model remote control (e.g. 2.4 Ghz)
  • a suitable model remote receiver (4 channels or more)

Wiring

The channel assignment is:

 left stick (left/right):  pinRemoteSwitch
 left stick (up/down):     pinRemoteMow
 right stick (left/right): pinRemoteSteer
 right stick (up/down):    pinRemoteSpeed

Videos

  1. demo


WIFI

This is an advanced topic - only use a WIFI module if your Ardumower is fully working. A WIFI module can be used as an alternative for Bluetooth communication. Again, pfodApp is required to connect WIFI and the phone.

https://github.com/FredericG-BE/ardumower/wiki/Using-ESP8266-WIFI-module-on-Ardumower

Realtime clock (RTC)

The robot requires a clock, so that it can start mowing automatically at certain time intervals (timer).

A realtime clock (RTC) returns current time (minute, hour) and date (day of week, day, month, year) - by the help of a battery (Lithium Ion LIR2032, 3.6v, 48 mAh) the time continues to run even if the robot mower is switched off.

Additionally, the RTC module contains an EEPROM memory (non volatile memory) that can hold 4K of permanent user data.

DS1307 module

Troubleshooting "Tiny RTC I2C module"

If your module is losing time/date, fix the circuit like this:

  • Remove D1, R6 and R4
  • Solder jumper wire in place of R6
  • Inspect crystal soldering - fix if necessary
  • Replace battery

Wiring

The RTC module is connected on the I2C bus of the Arduino Mega (in parallel with any other I2C modules).

 DS1307 Module SDA       — Arduino SDA Pin
 DS1307 Module SCL       — Arduino SCL Pin
 DS1307 Module VCC (+5V) — Arduino VCC (+5V)
 DS1307 Module GND       — Arduino GND

Note

If you experience communication problems when using multiple I2C modules on one I2C bus, it is recommended to reduce the length of the cables.


Arduino Dropsensor - Absturzsensor

Funktion:

Der Arduino Dropsensor oder auch Absturzsensor ist dafür gedacht den Mover vor abstürzen vor Treppenabsätzen oder ähnlichen zu schützen. Ebenso kann dieser eingesetzt werden um Inseln von Bäumen und Blumenbeeten zu erkennen. Voraussetzung dafür ist allerdings das dieser an der Graskante hin zur Insel mit einem kleinen Graben umgeben wird damit dieser zuverlässig erkannt werden

Anschluß:

Benötigt werden 2 IR Entfernungssensoren. Am besten sind solche geeignet die bereits in einem externen Gehäuse eingebaut sind. Diese haben auch auf der Rückseite eine Einstellmöglichkeit für die Entfernung bzw Empfindlichkeit. Die Standard Ausführung benötigt 3 Anschlussleitungen . +5V, GND, Signalleitung und haben eine Empfindlichkeit von ca 30mm – 800mm. Bei den Sensor den ich verwende handelt es sich um einen der gegen GND geschaltet wird. Dort habe ich zusätzlich eine Diode in die Signalleitung mit eingebaut um eventuelle positive Spannungen zum Bord zu blockieren und um einen eindeutigen Schaltzustand zu gewährleisten.


ohne eingbaute Diode

IR leuchtet bei Kontakt zur Oberfläche

Messung:

+ nach Signalausgang = 4,96V

- nach Signalausgang = 0V


IR leuchtet nicht über den Abgrund

Messung:

+ nach Signalausgang = 0V

- nach Signalausgang = 3,72V ( das hat mich gestört ) deshalb habe ich die Diode eingebaut


jetzt das ganze mit Diode in der Signalleitung

IR leuchtet bei Kontakt zur Oberfläche

Messung:

+ nach Signalausgang = 4,7V

- nach Signalausgang = 0V

IR leuchtet nicht über den Abgrund

Messung:

+ nach Signalausgang = 0V

- nach Signalausgang = 0V

jetzt 0V gemessen zwischen - und Signalausgang

Ich hatte bedenken gehabt das die 3,72V ein undefinierten Eingang schaffen was evl Probleme bei der Auswertung geben könnte.


Bekannte Probleme:

Ich habe die Beobachtung gemacht das wenn man die Entfernungseinstellung auf den Gras gegebenenfalls noch nach justiert werden muss. Ebenfalls ist mir aufgefallen das wenn die Sensoren auf eine nasse Betonoberfläche stoßen, irrtümlich annehmen das ein Abgrund erkannt wird. Da ich an meinen Testmower die Sensoren nur provisorisch angebracht habe, kann ich mir vorstellen das Fremdlicht zu Problemen in der Erkennung führt. Ich vermute daher, das wenn man die Sensoren vor Fremdlicht schützt, sich die Zuverlässigkeit auch weiter erhöht.

Evl ist es nötig mit Hilfe einer LED die Fläche zu beleuchten um immer eine gleichmäßige Helligkeit zu gewährleisten.


Relay

Using a relay, you can switch on/off external functions (light, horn etc.) on your Ardumower via pfodApp.

Wiring

                      GND o-----o GND Relais module 
                      +5V o-----o VCC Relais module           
 Ardumower pinUserSwitch1 o-----o IN1 Relais module
                                      Relais module  K1 o-----LED-----o LED supply voltage
                                      Relais module  K1 o-------------o GND

Pictures