Robotoy v3

simple robot v3 simple robot v3 simple robot v3
(click image for better view)

Here's my take on a simple microcontroller driven autonomous robot.  This is semi-permanent build of the previous robots, driven by a more powerful PICAXE 20M2 microcontroller.  The PICAXE and L293D motor controller are mounted on veroboard (stripboard) with screw terminals for the motor hookups.  But because I always think that I might want to add just 1 more feature, I mounted the I/O devices (LDRs, LEDs, and piezo) on solderless breadboard.  In addition to allowing the addition of new sensors, this also permits some flexibility in physical LDR placement.

The whole build is pretty simple, but here are some misc comments and observations:
  • As with all my projects, the code identifies itself on power-up.
  • I used too small a piece of veroboard and almost needed to mount components on top of each other.  You know you're too stingy on veroboard when you need to drill holes in the board margin just to add a sliding power switch.
  • The veroboard is mechanically attached to the solderless breadboard through a 4 pin header.  This doesn't provide any electrical connection, but is convenient for orienting the veroboard vertically.
  • This circuit needs a slide power switch because the standby current of the L293D is substantial.  A FET to power the L293D under PICAXE control would have reduced power draw, but is overkill for a toy.
  • Sharing a single power supply between the microcontroller and motors is, in my experience, always problematic.  Electrical noise can reset the microcontroller randomly and lead to tricky debugging sessions.  The L293D has built in diode protection, and I've mounted caps across the motors, and also across the supply for the PICAXE.  This seems to filter the supply voltage adequately.  But reducing electrical noise takes a bit of voodoo, so more filtering may be necessary with a different build configuration.
  • The M2 series can sense voltage.  Upon turning on, the robot indicates the battery charge by flashing the red LED up to 6 times (6=max charge).  btw, the red LED is mounted on the serial line (port a.0) so it doesn't consume one of the 20M2's real i/o output lines.
  • The motors are driven by a simple photophile (or photovore) algorithm.  When the light difference on the LDRs is large enough, then the robot turns toward the light.  As you can see from the video below, it's pretty neat how 2 LDRs can provide some semblance of object avoidance. 
  • The 4 LEDs in the front play random patterns, or flash with the music.
  • The robot will randomly stop and play any of about 20 different tunes.  If you're lucky enough to witness the Addams family tune, then you'll see the robot dance. 

Robotoy3 in action:
The electronics should drive almost any simple robot chassis.  I had the Pololu robot chassis and Tamiya twin-motor wheel assembly from a previous version of this robot.  The rear third wheel is a "ball caster".  All of these items are well made and compatible.

The following schematic/layout drawing was generated from this file using PEBBLE (Picaxe Electronic Bread Board Layout Emulator - V3.1).

simplest clock schematic

(click to enlarge)

Parts count:

  • 1 Picaxe-20M2 microcontroller
  • 1 L293D H-bridge motor controller
  • 2 light dependant resistors
  • 5 LEDs
  • 1 piezo speaker
  • 2 resistors (10K, and 22K; for in-circuit programming)
  • 1 3-pin programming header
  • misc wire, DIP sockets, a battery holder, veroboard, solderless breadboard
  • Pololu robot chassis rrc01a (transparent yellow)
  • Tamiya 70097 twin-motor gearbox kit
  • Tamiya 70101 truck tire set kit
  • Tamiya 70144 ball caster kit

My schematic is above, and here is the code.  My style/documentation is pretty rigorous, but I strongly advocate good coding practice regardless of the machine; all software only becomes more obfuscated over time.

This code is explicitly released under the GPL. And this page is licensed under a Creative Commons Attribution 2.5 License.  

Write me if you find this project interesting. Link to this page if you find it relevant..

Warning, may cause loss of time. This project is provided without any warranty and probably isn't suitable for anything.

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