To date, this is my most successful design. It is powered by an Atmel 8535, which means you can write fairly complex applications (8Kb flash). It has 4 tactical sensors, two eyes based on LDR resistors placed in a tube to have directional sensory, one RC5 Ir diode to be able to command the robot using a standard remote control unit and expansion bus on the top of the vehicle (Wireless module has been build).
This small robot measures 75x38x50 mm, and is powered by two geared DC motors . Four NiMH cells, delivering 120mAh at 1.2 V each provide enough power for approximately 1 hour autonomy. The brains of the robot are made up of a AT90LS8535 running at 4MHz in a TQFP package. The motors are driven by a 74AC244, an octal buffer/line driver which I used to make 2 H-bridges.
The robot has 8 sensors; 4 touch sensors on each corner, two directional LDR light sensors, one IR sensor (TSOP1736, RC5 type) and one proprioceptive sensor indicating battery status. This sensor package seems to be enough to provide for rather intelligent behavior.
The robot has a tank like locomotion. I've grown fond of this type of locomotion as it provides traction on all wheels. Also, I really enjoy the skid steering.
The robot has 4 connectors; one to charge the batteries, another one to program the robot, a serial connector and one expansion bus, exposing 8 data lines, from which 4 our ADC capable. I've build a wireless module to put on top of the robot. More on that will follow, sufficient to say now that it uses a BIM2 transceiver from radiometrix. I've experienced some troubles getting the PCB ready for the PC host adapter, as I had to redo the PCB for a few times to get it right . Hence, I put the wireless module on a lower priority.
The next code is a small BASCOM program that can drive the MicroRover. It is a simple subsumption architecture, using 3 behaviors; photofobic, wandering and react to touch.
You can read more about the subsumption architecture in the following wikipedia article about subsumption architecture .
'( r o v e r --------- test code for rover based on 8535 ') M1A alias portd.7 M1B alias portd.6 M2A alias portc.1 M2B alias portc.0 BAT_CONTROL alias portc.4 const BAT_LEVEL = 5 TOUCH_BACK_LEFT alias pinc.5 TOUCH_BACK_RIGHT alias pinc.6 TOUCH_FRONT_LEFT alias pind.4 TOUCH_FRONT_RIGHT alias pind.5 EYE_CONTROL alias portc.7 const EYE_LEFT = 7 const EYE_RIGHT = 6 config Adc = Single , Prescaler = Auto config debounce = 10 config Rc5 = pind.2 enable interrupts ' -- subroutine declarations declare sub forward declare sub backward declare sub turn_left declare sub turn_right declare sub halt declare sub diagnostics declare sub motor declare sub touch declare sub photofoob declare sub wander ' -- variable declarations dim eye_l as Word dim eye_r as Word dim bat as Word dim tch_bl as bit dim tch_br as bit dim tch_fl as bit dim tch_fr as bit dim c as byte dim rc5_address as byte, rc5_command as byte dim temp as byte dim i as integer ' -- define behaviours ' . global settings const BEAT = 50 ' -- unit of execution time ' a behaviour will use this as a standard ' time tick for action const BEAT2 = 100 ' . touch dim touch_state as byte ' - state of the 'touch' behaviour dim touch_dur as word ' - duration dim touch_turn as byte dim touch_direction as byte ' . motor dim motor_vector as byte ' - drive vector for motors const M_STOP = 0 const M_FORWARD = 1 const M_RIGHT = 2 const M_BACK = 3 const M_LEFT = 4 ' . photofoob dim photofoob_state as byte dim photofoob_turn as byte dim photofoob_dur as word dim photofoob_offset as word ' . wander dim wander_state as byte dim wander_turnorgo as bit dim wander_dur as long const WANDER_RUN = 200*BEAT ' -- main DDRD = &B11001011 DDRC = &B10011111 start Adc set PORTC.6 set PORTC.5 set PORTD.5 set PORTD.4 wander_state = 0 photofoob_state = 0 photofoob_offset = 50 touch_state = 0 motor_vector = 0 do ' pull in data from the sensors gosub latch_sensors ' behaviours photofoob wander touch ' override controls now with RC5 commands ' gosub remote ' motor control motor temp = inkey() if temp > 0 then call diagnostics end if loop ' -- control the engine sub motor select case motor_vector case M_STOP: call halt case M_FORWARD: call forward case M_BACK: call backward case M_LEFT: call turn_left case M_RIGHT: call turn_right end select end sub ' -- Pull the sensory data into globals latch_sensors: set EYE_CONTROL waitus 250 c = EYE_LEFT eye_l = getadc(c) c = EYE_RIGHT eye_r = getadc(c) reset EYE_CONTROL set BAT_CONTROL waitus 250 c = BAT_LEVEL bat = getadc(c) reset BAT_CONTROL tch_bl = TOUCH_BACK_LEFT tch_br = TOUCH_BACK_RIGHT tch_fl = TOUCH_FRONT_LEFT tch_fr = TOUCH_FRONT_RIGHT return ' -- remote: getrc5( rc5_address, rc5_command) if rc5_address <> 255 then rc5_command = rc5_command and &B10111111 select case rc5_command case 32: motor_vector = M_FORWARD case 33: motor_vector = M_BACK case 16: motor_vector = M_RIGHT case 17: motor_vector = M_LEFT case 12: motor_vector = M_STOP case 14: call diagnostics end select end if return ' -- print out some diagnostics sub diagnostics print "el "; eye_l print "er "; eye_r print "ba "; bat print "wd "; wander_dur print "bl "; tch_bl print "br "; tch_br print "fl "; tch_fl print "fr "; tch_fr print "vc "; motor_vector end sub ' -- move forward sub forward set M1A reset M1B set M2A reset M2B end sub ' -- move backward sub backward reset M1A set M1B reset M2A set M2B end sub ' -- turn right sub turn_right set M1A reset M1B reset M2A set M2B end sub ' -- turn left sub turn_left reset M1A set M1B set M2A reset M2B end sub ' -- stop rover sub halt reset M1A reset M1B reset M2A reset M2B end sub ' ------------------------------------------------------------------------ ' -- B E H A V I O U R S ' ------------------------------------------------------------------------ sub touch ' we always react to touch, even when processing a touch if tch_bl = 0 then touch_turn = M_RIGHT touch_direction = M_FORWARD touch_state = 1 touch_dur = BEAT2 end if if tch_br = 0 then touch_turn = M_LEFT touch_direction = M_FORWARD touch_state = 1 touch_dur = BEAT2 end if if tch_fl = 0 then touch_turn = M_RIGHT touch_direction = M_BACK touch_state = 1 touch_dur = BEAT2 end if if tch_fr = 0 then touch_turn = M_LEFT touch_direction = M_BACK touch_state = 1 touch_dur = BEAT2 end if select case touch_state case 0: case 1: motor_vector = touch_direction if touch_dur = 0 then touch_state = 2 touch_dur = BEAT2 end if decr touch_dur case 2: motor_vector = touch_turn if touch_dur = 0 then touch_state = 0 touch_dur = 0 motor_vector = M_STOP end if decr touch_dur end select end sub sub photofoob select case photofoob_state case 0: ' we kick into action when it is too light if eye_l > photofoob_offset or eye_r > photofoob_offset then photofoob_turn = M_LEFT if eye_l > eye_r then photofoob_turn = M_RIGHT end if photofoob_dur = BEAT photofoob_state = 1 end if case 1: motor_vector = photofoob_turn if photofoob_dur = 0 then photofoob_state = 2 photofoob_dur = BEAT end if decr photofoob_dur case 2: motor_vector = M_FORWARD if photofoob_dur = 0 then photofoob_state = 0 motor_vector = M_STOP end if decr photofoob_dur end select end sub sub wander select case wander_state case 0: i = rnd(100) i = i * 10 wander_dur = i * BEAT wander_state = 1 case 1: if wander_dur = 0 then wander_state = 2 wander_turnorgo = 0 wander_dur = WANDER_RUN end if decr wander_dur case 2: if wander_turnorgo = 0 then motor_vector = M_LEFT if eye_l < eye_r then motor_vector = M_RIGHT end if else motor_vector = M_FORWARD end if if wander_dur = 0 then wander_state = 0 motor_vector = M_STOP end if decr wander_dur i = wander_dur mod BEAT2 if i = 0 then toggle wander_turnorgo end if end select end sub
The most primitive behavior is reaction to touch, this behavior can subsume over all other tasks. Most of the time, the robot is in a photofobic state, it will wander of to a dark place by constantly steering in the most dark direction. Light values are measured by an ADC channel on the AVR MPU. Whenever the robot reads the light intensity on its two eyes, it'll power the LDRs for a short time and - enough time for the ADC to setlle - and then read out the intensities (lines 149-155). This intermittent powering of the LDRs prevent battery drain. When the light intensities falls below a certain threshold, the robot will sit happy until light levels are up again.
Whenever an object hits one of the touch sensors, the robot will try to turn away from the obstacle by reversing its direction and turning towards the opposite site of the touched sensor. If both front or aft sensors are touched, the robot just reverses direction, no turn takes place (lines 250-302).
After a random time, the rover wants to wander around. This wandering behavior has priority over its photofobic state, but lower priority than the touch behavior. When in wandering state, the robot is attracted to light. It will run of as fast as it can to brightest spot it can detect. The time that the robot wanders around is determined by another random number. I've found that this wandering state is very usefull for the robot to roam the complete room. If the wandering behavior would not be included, the robot would simply drive to a dark spot and sit there until light intensities are high enough to get it moving again. With the wandering behavior, though, the robot can sit idle on a dark spot, come to life again and run straight into the light. When the wandering behavior shuts down, the robot gets a panic attack and hurries to the nearest dark spot it can find (lines 337-374).
Lines 171 to 190 implement code to steer the robot via a TV remote control. The remote control can steer the robot in all 4 directions. Moreover, it can let the robot dump its internal state to its serial port. This can come in handy when debugging.
Although the battery level is already measured (lines 157-161) , by comparing a constant voltage drop over 3 diodes against the battery voltage, nothing is done with it. The idea is to have a small hardware extension on the robot that allows it to charge automatically. This extension can be made of just two wires that can connect to a docking station, composed of two metal plates. The idea is to let the robot navigate to a charging station as soon as battery levels drop below a certain treshhold. Moreover, the idea is to use the LDRs to navigate to the charging station. A LED, pulsating at a low enough frequency can be easily detected by the LDRs. The LED would indicate the position of the charging station.