Encoder Front Page
SRS Home | Front Page | Monthly Issue | Index
Google
Search WWW Search seattlerobotics.org

Back to main article

Upper section: sonars, servos, voice board and heat sensor.

The upper section was intended to hold the sensors. The black box is the sensor pod. Which holds five Polaroid sonar units and one Pyroelectric heat sensor which will detect the heat wave lengths of humans and candles.

The two eyes in front allow it look forward and see in "stereo". We humans need that for depth perception, but the sonar gives depth readings. But with only one sonar the robot can know something is out there at four feet, but if the object moves you can not know if it moved left or right, just the fact it moved. But with two sonar if a object moves to its left, then the left sonar will still "see" an object, but the right will not, thus you know which direction the object is moving in relation to the robot.

As a test, I wrote a program that allows the "head" to track, as I u walked around the front of the robot. As I walked back and forth the head can follow me as I move.

robot sensor pod.jpg (37054 bytes)
Picture to the right is a view from the side and back. On each end of the sensor pod is a sonar, which I call the left and right ears.

The purpose of these "ears" is to look sideways to walls so they can be easily tracked without the pod being moved.  I went ahead and put a sonar in the back of the head so it could look back (like your mom with eyes in back of her head). By having a sensor at the four corners of the pod, the robot has to only rotate its head 90 degrees to map its surroundings all 360 degrees around it.

I tried putting all the sonars as close to the center of the robot as possible. The sonar has about a 5 inch minimum distance it can measure and it can not give you distances any closer than that. The front and back sensors are about 4 inches from the edge of the robot so that the robot will be able to see things just 1 inch from its front and back edge. The ears are about 3 inches in from the side and so they can see things that are as close as 2.5 inches from its side.

Also pictured here is the V8600 voice board. It provides a text to speech capability. So your robot can talk back to you using very little memory since you only have to give it text words and this board does the converting into speech. It is a very cool board.  Click here to go to the page that has a demo wav file to hear what it sounds like.  The text file it plays from is a standard ASCII text file with some control codes.

robot sensor pod back.jpg (33536 bytes)
The pod is placed on two servos that allow the pod to rotate 180 degrees left to right and almost 180 degrees up and down. So the robot can look around  its environment without moving its body.

Controlling the servos was one of the easier things to do with the B32. B32 has four different pulse width modulation (PWM) sub-systems that can put out pulses that can directly control two servos and the two motors, having a different duty cycle for each.

Once the B32 CPU gives the sub-system the parameters, it never has to take CPU cycles again from the main processing.

robot sensor pod servos.jpg (42470 bytes)
Pictured to the left is the back of the sensor pod opened up. Stuffed inside are the five sonar transducers, five relays and one heat sensor.

Having five sonar sensors on one robot did not prove to be that simple. The problem was whether to have one module for each transducer and multiplex the modules together or to have one control module multiplexed to the five sonars.

I tried multiplexing five of the modules together but they did not work correctly. So I went to having one control module multiplexed to five sonars. Each module is tied together to a common ground, the line that delivers the 400V pulse and then listens for the return is what was multiplexed together.

I tried using solid state switches for the multiplexing for speed and no noise, but I could not get the right solid state switch to work with the module and sonar. So I decided to use reed switches. I was surprised how fast they switched. I was afraid I would have to wait for the reed switches to close and stop bouncing, but these switches were switching in the sub-millisecond range which is as fast as some of the solid state switches. They are Hamlin HE721A0510 from Digikey ($2.70). They have built in voltage suppression diode.

robot pod inside.jpg (47225 bytes)
The picture to the right is the bottom of the top section. You can see the servo bottom sticking out and the sonar module, and also the DB9 connector that the middle section plugs into.

I will go into detail about this whole setup in a future article.

Robot top bottom of.jpg (28650 bytes)
Not pictured here and not mounted yet is the speaker for the voice board and the serial transmitter.

I used to have the Ming TX-99 and RE-99 which would transmit the serial data allowing the robot to be tested as it roams around. But I found them too slow and they would drop data. So I spent the big bucks and bought InfoWave serial transmitters which will be mounted on the upper section somewhere.

I haven’t even had time to test the InfoWave unit yet. It runs on a 5V supply and is a transceiver of serial or parallel data at 85kb tranmitting using 900mhz spread spectrum and is supposed to be good for 300 feet indoors and 800 feet indoors.

I have also bought one of the X10 2.4 GZ video transmitters. Someday, but not for the Fire Fighting contest, I will put in a small camera mounted on top of the sensor pod.  We have tried transmitting DVD video from Benjamin's computer upstairs and receiving the signal downstairs on the TV.   They work great and the price was right.

In future months, I will write articles going into detail the various sub-systems.

 

Back to main page.

Go to  lower section.

Go to middle section.