Introduction: Obstacle-Avoiding Robot With a Personality!

Unlike most roaming 'bots, this one actually roams in such a way that it actually seems to be 'thinking'! With a BASIC Stamp microcontroller (Basic Atom, Parallax Basic Stamps, Coridium Stamp, etc.), a chassis of some kind, a few sensors, and some sophisticated code from this instructable, you can create a robot that will execute movements you never even programed into it!

Here's a video (it's kind-of low quality, but I'm working on that. (I am still trying to work out the part that it's too slow.)

Step 1: The Sensors

The (name?)...Well, let's just call it Bob. Bob has five sensors

  • Ultrasonic Rangefinder (aka "sonar")
  • 2 Sharp GP2D12 IR Sensors
  • 1 Standard IR Assembly (more on this later)
  • 1 CdS (Cadmium Sulphide) Photocell

The ultrasonic rangefinder helps Bob see obstacles that are right in front of him; they also tell him what distance the object is from him. This can be obtained from many sources. You can find them from (Parallax ; they call it the "Ping)))"), Acroname, HVW Technologies, and so many more sites. No matter where you go to find them, they all cost about the same (~ $30). The two IR sensors made by Sharp are very easy to use when used for simple object detection as in this case. You can get them at may online stores, such as the ones listed above. They help Bob see obstacles that the ultrasonic rangefinder can't; obstacles that are coming too close to the sides of the chasis. They cost about $12 to $15 depending on where you get them. The "IR assembly" I made myself; see step 2 for assembly. The CdS Photocell (or light-variable resistor, whatever your preference) is for detecting changes in ambient lighting. Bob uses them to know when he's in a dark or light room.

If anyone who has prior experience with any of the Sharp IR rangers, FYI, they are not being used for actual distance measurement in this robot. I do not have an ADC (Analog-to-Digital Converter), neither do I know how to use them that way. They are simply providing a HIGH or LOW signal to the BS2 microcontroller.

The datasheets for the Sharp IR's as well as the Ping))) sensor can be found on the net, but if you're lazy like me, you can scroll down a little further an there they are!

Step 2: The Hardware, Brain, and Other Components

Ok. To start off, the hardware that was used for this robot was part of a kit I got. It is the "Boe-Bot" kit from Parallax (, but this design is very flexible; you can use any chassis you want, just be sure that 1) the ultrasonic rangefinder is at the highest elevation on the robot so it doesn't hit bottoms of railings, etc, and 2) the IR sensors are angled in such a way that they can even detect objects that are about 1" away from the robot. This keeps it from hitting edges of things that may hit the wheels.

Mounted on the chassis is Parallax's Boe-Board which came with my Boe-Bot kit, which is simply a development board that can be used with any Stamp microcontroller with the same voltage requirements and pin layout. There are many different Stamp development boards on the internet. It is $65 from Parallax.

On the dvelopment board, as Bob's brain, is the BS2e (BASIC Stamp 2 e), which is basically the same as the BS2, except with more memory (RAM and EEPROM). The EEPROM is for program storage, and the RAM is for storing the variables (temporarily, of course). Bob may not be the fastest thinker in the world (~4,000 instructions/sec), but hey, that's good enough.

Bob moves via two continuous rotation servos from Parallax which, as many servos do, have a LOT of torque. For the juice, he has a 4-cell AA battery pack (for a total of 6V) connected to the 5V regulator on the development board, which gives a steady output of, you guessed it, 5V as to not fry the components. Many devices for robotics run on either a 5V or 6V supply; for some reason, it's a standard. And you DON"T want to fry these components; they're expensive. The BS2e has an internal regulator, but don't give it more than 9V if you are not using a development board! Also, if you don't use a development board (which always have regulators), then BE SURE to use a 5V regulator.

NOTE: As for power consumption, Bob is very greedy. Use RECHARGEABLE batteries for this; they last a LOT longer. I used 4 Energizer rechargeables @ 2500ma each, which definitely prolongs the life.

Step 3: Assembling the Light Sensor Circuit

The light sensor requires a circuit for the BS2e to properly utilize it. I got this circuit right out of one of Parallax's books (actually, the one that came with my kit). NOTE: PIN 6 IS ACTUALLY PIN 1; THIS MUST MATCH THE CODE OR YOU MAY DAMAGE OTHER COMPONENTS. BE CAREFUL NOT TO MESS THAT UP.

Step 4: Assembling the Dropoff Detector

This can be put together on some bare PCB. I just ran over to RadioShack and got one, and snipped the board to fit the circuit. This part is CRUCIAL. If you mess this up, poor Bob may die. The IR detector is a Panasonic PNA4601, but you can get them from RatShack, as well as the resistors and the IR LED. It does not matter what size IR LED you get, juts make sure it's not an IR PHOTOTRANSISTOR. That is a TOTALLY different device. Also, you must use heat shrink tubing or some sort of straw (you can spray-pain it black) to narrow the beam of the IR LED, but it has to be completely sovered (except the end of the LED), or the sensor will NOT work. I used a plastic casing from Parallax. You can order the LED and the casing on their website.

Unfortunately, the frequency range on the IR detector I used was very wide, which means it is much more prone to interference. Luckily, RadioShack offers ones only tuned to 38Khz, which means Bob is less likely to act strange around remote controls and other devices that use IR. The DP2D12's are great because they are virtually interference-free because of advanced optics (the lenses) and circuitry. In future projects, I will not be using regular IR detectors. The Sharp IR's are preferable over simple IR receivers.


Step 5: Bob Needs Sound!

Connect a piezo speaker to PIN 5, and - to ground. Bob needs to express himself! The best kind of piezospeaker to use would be a surface mount one. They are almost always 5 volts. Otherwise, if you use one rated below 5V, you are going to need a resistor.

Step 6: Adding the 'Headlight'

To make Bob look cooler in the dark, he turns on a headlight when he enters a dark room. Any white LED will work for this. Since the circuit is so darn simple, I am just going to tell you: just use a 220ohm resistor to limit the current. And or course, - goes to ground.

Step 7: Fill Up Bob's Brain!

Here is the code for Bob. It is broken up into sections: declarations (constants and variables), initialization, the 'main' loop, and subroutines. The type of programming that I used is Subsumption-Based FSM (Finite State Machine) Architecture. Basically, it makes the robot run faster, and better organizes the code. If you want to venture into that relatively complex realm, read the PDF on this page. I have added comments (the text in green) to help identify different parts of the code.

All the connections to the BS2e are listed again below

  • PIN 0 - 220ohm resistor to the CdS photocell
  • PIN 5 - positive lead of piezo speaker
  • PIN 6 - SIG (signal) line of left GP2D12 (left when looking at the robot from above)
  • PIN 8 - SIG line of right GP2D12
  • PIN 9 - OUT (output) line of the IR detector (dropoff sensor)
  • PIN 10 - 1Kohm resistor to the positive lead of the IR LED
  • PIN 15 - SIG lead of ultrasonic rangefinder

Bob's code is written in such a way that

1) He, or course, avoids objects and dropoffs
2) counts the number of times each one of the sensors was triggered, and determines if he's in a spot that cannot be maneuvered in
3) generates pseudo-random numbers to randomize movement
4) turns on "headlights" after determining that he's in a dark room by using timers and IF...THEN statements

I am still working out the 'lag' part. It has to do with the discharge time of the capacitor for the light sensor, as well as an over-burdened BS2e.