Getting it all together -- Raspberry Pi talking to the Arduino UNO talking to the L298N dual H-bridge makin’ wheels turn

All setup for some code and connection testing

My project manager (Kylie) is back home now so the project engineer (me) is trying to get a step or two ahead of her…  She’s expecting progress by the time we get together again!

Power:  I’m using a rechargeable LiPo USB battery to power the +5V for the RPi and Arduino and a separate set of 8 rechargeable NiMH AA’s (9.6V) for the motor power to the L298N.

Motors and motor drivers:  The chassis we’re using has 4 DC motors (3-12V) and I’m using a SainSmart L298N dual H-bridge module to drive each pair.  At the moment I only have one H-bridge, so for testing I’m driving the two rear motors.  My plan is to connect the second H-bridge to the front motors in a way that the code will drive the left and right wheels as pairs for maneuvering (if anyone knows why that’s a good or bad idea please let me know…). 

Arduino to L298N:  The connections from the Arduino to the L298N are pretty straightforward.  See the pics at the side of this page for reference.  If you want to vary the motor speed you have to remove the jumpers the ENA and ENB pins in order to provide a PWM signal from the Arduino. Then you have to provide a digital output pin for each of the four inputs on the L298N (IN1 & IN2 control motor A and IN3 & IN4 control motor B).  Finally, don’t forget to connect GND – GND.  Of course the NiMH battery pack is connected to the motor power block with + to VCC and – to GND.  You can leave the 5V empty since the board has an onboard regulator to provide the logic circuits the 5V from the motor power inputs. 

So, my pin connections are:

Arduino (digital)           L298N            Comment

pin 2                               IN1                  motor A direction

pin 3                               ENA                motor A speed; needs to be a PWM output pin

pin 4                               IN2                  motor A “brake”

pin 5                               IN3                  motor B direction

pin 6                               ENB                motor B speed; needs to be a PWM output pin

pin 7                               IN4                  motor B “brake”

In the Arduino sketch, you control the motor direction by setting IN1 (or IN3 for motor B) to HIGH or LOW and then “releasing the brake” by setting IN2 (or IN4 for motor B) to the opposite.

i.e.:

IN1 = HIGH  using digitalWrite

IN2 = LOW   using digitalWrite

ENA = 127   using analogWrite to set PWM

Will spin the motor in one direction at 50% (PWM values go from 0 – 255).  Reversing IN1 and IN2 will reverse direction. 

Hope that was clear enough…  I’ll post the code as soon as I get it initially tested.

BTW, here is a good place to make some acknowledgements:

1.    Username cbrittian1 provided a super “Instructable” (see link) that I followed pretty closely to get up and running and I’ve shamelessly “stolen” his code as the core for my project.  That’s the beauty of open source…  hopefully I’ll contribute some modifications and improvements along the way.

2.    At work we have an excellent robotics team, and Scott in particular has been a key “consultant”, turning me on to the Raspberry Pi in the first place, explaining the electronics details, and  pointing out a few things that should have been more obvious to me but weren’t.

3.    And of course there are many, many other great discussions and contributors out there that I’ve leveraged for this project.  For example, this YouTube video  is excellent for setting up your USB WiFi dongle.  It gives a link to a script as well.

RPi talking to the Arduino:  I plan to use the I2C for communications to / from the RPi and Arduino.  That’s the way cbrittian1 did it.  I’ve written and tested some very basic USB serial code but I didn’t want to rewrite his code, so I2C it is, at least for now.  Plus, by powering the Arduino from the 5V GPIO from the RPi, the vehicle won’t have to carry around the USB cable and I can still use it for code development and uploading.  I’ve ordered a couple 4-channel I2C-safe Bi-directional Logic Level Converters but haven’t received them yet.  Even though there are a few articles out there saying if you have the RPi set up as MASTER that it’s OK to direct connect the SDA / SCL pins because they have pull up resistors, I don’t want to take that chance yet so, now I wait…