In this, part 3 of the “Giving new Life to an Old Toy Car” series, we will be adding some flashing lights to the toy car project. This will ultimately serve two purposes, with the most obvious being to give some life and excitement to the project ( as the final user will be a young boy of 7, the visual aspect is important). The second purpose is more obscured, and mostly only useable to programmers and coders, or those that will debug the project… The flashing lights will function as status indicators, at startup, as well as during the normal operation of the toy. Obviously, the diagnostic nature should be well obscured so as to not distract from the visual aspects.

A short test of the display unit, disguised as a “police-style” flasher unit

The flasher unit is made up of an extremely simple circuit, with only a PCF8574 IO expander, bypass capacitors, some LED lights, and current limiting resistors.

The bottom layer of the flasher unit, shows the Io expander, bypass capacitors, and current limiting resistors.

The top layer is designed to be as clean as possible, with only LEDs and some labeling

Schematic

Schematic

The schematic is straightforward, with no surprises, consisting only of a few components, like the PCB8574, bypass capacitors, current limiting resistors, and of course the LEDs. It is also important to remember that I plan to use this entire robot car to teach a young boy to program microprocessors. I believe that visual is best, thus, all the lights ??

Coding

As this is still a project in quite a lot of development stages, I will not publish my exact code at this moment. You can however look forward to the future conclusion post, which will contain all my code at that stage.

For now, however, we need to keep in mind that the PCF8574 is an I2C port expander, with an 8-bit IO port.

It is thus possible to do something simple like the below:

#include <Wire.h>

void setup() {

wire.begin();

wire.beginTransmission(0x20);

wire.write(0b11111111); // All LEDS off

// our circuit is sinking current into the io expander

wire.endTransmission();

delay(1000); // delay for illustration purposes, production code will use

// non blocking code

wire.beginTransmission(0x20);

wire.write(0b10100101); // All blue LED on

// our circuit is sinking current into the io expander

wire.endTransmission();

delay(1000);

}

void loop() {

}

Obviously, this is just a very quick example and is meant to just test functionality. Your own application will ultimately determine the exact code that you would need.