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AUTONOMOUSE HEROBOT T   Pt 1: By JOHN CLARKE This clever little robot runs around the floor and stops if it finds anything in its way. It then turns to one side or the other and moves forward again. Light chasers run in one direction or another, depending on what it’s doing. 18  Silicon Chip Fig.1: the block diagram comprises three main sections: light sensing, forward/reverse motor control and the light chas­ers. A UTONOMOUSE THE ROBOT is autonomous – it runs around by itself without any need for its controller (you) to direct it in any way. It will “see” objects in its way and can turn away from them or reverse to avoid collisions. It also has a variety of light displays which vary according to its actions. Its features include: •  Forward and reverse light chaser. •  Clockwise and anticlockwise turning light chaser. •  Rear flashing light. •  Steers away from objects. •  Reverses from potential collisions. •  Adjustable speed. •  Adjustable sensitivity of object detection range. •  Object sensing immune to effects of normal ambient light. •  Automatic slowing before reversing to prevent motor/gear damage. Autonomouse the Robot moves on three wheels, with two at the front and a swivelling castor at the rear. The side wheels are independently driven to allow the robot to steer and reverse. Autonomouse is built as a basic shell using several PC boards soldered together. The two “eyes” are located on the front of the case and provide the robot with straight-ahead and periph­eral vision. It is dressed with red transparent acrylic on its front, top and rear. Autonomouse will steer away from an obstacle it detects with its peripheral vision. If this is not effective in avoiding the object, the robot will stop, reverse up and turn around. An object directly in front of the robot will cause it to reverse up and turn directly. When Autonomouse travels forward, a row of eight LEDs at the front flash sequentially from top to bottom to show the direction of travel. If Autonomouse reverses, the LEDs chase from bottom to top. At the top of the robot are eight LEDs arranged in a circle which sequentially chase clockwise or anticlockwise whenever it turns left or right. This chaser does not operate if the robot is going forwards or in reverse. Fig.1 shows the block diagram of the Robot. It comprises three main sections: light sensing, motor control and the light chasers. The light sensing section has a 38kHz driver which modu­lates infrared LEDs. There is an IRLED and sensor associated with each sensor, one for the right, one for the centre and one for the left. The IR sensors will detect infrared signals at 38kHz and reject any other light signals. This makes them much less sensi­tive to natural light or other September 1999  19 Fig.2: the circuit has several sections which are duplicated, such as the left and right motor drivers, the two 8-LED chasers and the left and right timers (IC2, IC4). 20  Silicon Chip September 1999  21 Fig.3: these waveforms show the operation of the 38kHz drive to the infrared LEDs. The top trace is the output at pin 3 of IC1 at 4V peak-to-peak. The lower trace is the voltage at the base of transistor Q1. Fig.4: these waveforms show the operation of the infrared detec­tors. The top trace shows the output from one of the infrared detectors in the presence of a relatively strong 38kHz IR signal. The output is low for most of the time. The lower trace is the infrared detector output in the presence of a weaker 38kHz sign­al. It is low for only some of the time. Fig.5 (left): these oscilloscope waveforms show the operation of IC8a which produces the pulse width drive for the H-bridge drive circuits to the motors. The lower trace is the triangle waveform at around 400Hz. This triangle waveform is compared with the voltage at pin 2, shown by the straight line. The output is the top trace which goes high whenever the triangle waveform is above the voltage at pin 2. light sources such as incandescent or fluorescent lights which produce a 100Hz modulated signal. When a sensor detects a 38kHz signal, it will produce an output to indicate that there is an obstruction in the way. The robot will steer left if it detects a relatively weak signal from the right detector and steer right if it detects a weak signal from the left sensor. If any of the detectors receive a strong reflected signal, the robot will reverse to avoid the obstacle. Output from the left sensor is used to trigger right timer IC2 and reverse timer IC3. Similarly, the right sensor output triggers the left timer IC4 and also reverse timer IC3. When a weak signal is received by the left infrared detec­tor, the right timer is triggered but there is insuf22  Silicon Chip ficient signal to trigger the reverse timer. A strong signal received by the left infrared detector will also trigger the reverse timer. Similarly a weak signal to the right detector will only trigger the left timer, but a strong signal will trigger the reverse timer as well. The right timer drives the forward/ reverse circuitry which controls the right motor. If the right timer is not triggered by the left infrared detector then the motor is driven in the for­ ward direction. The motor reverses whenever the right timer is triggered. The two LED chasers each comprise an up/down counter (IC10 or IC12) which drives a one-of-10 decoder (IC11 or IC13) which then drives eight LEDs. Reverse timer IC3 makes the counters count down rather than count up and this changes the direction of the LED chaser. Circuit description Fig.2 shows the full circuit details. IC1 is powered from a 6V battery via switch S1a while the other ICs are powered at 5V via low dropout regulator REG1. The motors are powered from a separate 6V battery and switch­ ed via S1b. We use two battery packs so that the heavy load drawn from the motors does not have any effect on the control circuitry. IC1 is separately powered from 6V to prevent its oscillation entering the 5V supply rail and being injected into the very sensitive infrared detectors IRD1 & IRD2. IC1 is a 555 timer running at 38kHz to drive the IR LEDs. The 38kHz output at pin 3 is clamped to an am- plitude of 0.6V by diode D1. This is done to maintain a constant signal level re­gardless of the battery voltage. Following D1, the signal is lightly filtered with the 3.3kΩ resistor and .0033µF capacitor and fed to trimpot VR2 which sets the signal level to transistor Q1 which functions as an emitter follower to drive the three IRLEDs via separate 470Ω resistors. The oscilloscope waveforms in Fig.3 show the operation of the 38kHz drive to the infrared LEDs. The top trace is the output at pin 3 of IC1 at 4V peak-to-peak. The lower trace is the voltage at the base of transistor Q1. Note that the vol­tage is nominally at +2.6V with a 360mV 38kHz modulation swing. Note that each IRLEDs is driven at a nominal 1.2mA which is then modulated at 38kHz. This is to make sure that the 38kHz signal from each LED is about the same. The infrared light from the three IR LEDs is picked up by infrared detectors IRD1 and IRD2. These comprise an infrared optotransistor, preamp­ lifier and 38kHz filter circuitry. A strong 38kHz infrared signal will cause the IRD output to go low. This is shown in the waveforms of Fig.4. The top trace shows the output from one of the infrared detectors in the presence of a relatively strong 38kHz IR signal. The output is low for most of the time. The lower trace is the in­frared detector output in the presence of a weaker 38kHz signal. It is low for only some of the time. The output from IRD1 triggers the right timer IC2 via the 27kΩ resistor and diode D2. Pin 2 of IC2 needs to be pulled below about +1.7V in order to switch the timer output at pin 3 to a high level. This means that the output from IRD1 must be low for more than 2/3rds of the time. IC2’s output stays high until pins 2 & 6 reach about +3.3V and then pin 3 goes low. The 1µF capacitor at pins 2 & 6 effectively integrates the output of IRD1. So pins 2 & 6 are pulled down by IRD1 and pulled up by the 390kΩ resistor. The output from IRD1 also triggers reverse timer IC3 via diode D3 but here the filter components at pins 2 & 6 are a 10µF capacitor and a 100kΩ resistor. These components mean that the output from IRD1 must be low most of the time in order to trigger IC3. In fact, if IRD1’s output were permanently low, the voltage at pin 2 Parts List 1 PC board, code 08409991, 114 x 145mm (Board 1) 1 PC board, code 08409992, 114 x 128mm (Board 2) 1 PC board, code 08409993, 114 x 72mm (Board 3) 2 motor/gearbox drives (Jaycar YG-2725) 2 4 x AA cell holders and battery snaps 8 AA alkaline cells 1 DPDT miniature toggle switch (S1) 1 plastic panel, 75 x 110 (battery support panel) 1 piece of double sided PC board, 114 x 69mm (rear panel) 1 piece of single sided PC board, 45 x 105mm (castor bracket) 2 35 x 20mm pieces of PC board (motor/gearbox mounting) 3 pieces of red transparent acrylic, 60 x 90mm, 60 x 140mm and 60 x 60mm 2 64mm diameter wheels (see text) 1 30mm furniture castor 12 15mm long tapped spacers (Perspex or Acrylic mounting) 6 9mm long tapped spacers (rear Perspex panel and motor mountings at motor end) 4 6mm long tapped spacers (motor mounts gear end) 26 M3 x 6mm screws 4 M3 x 15mm screws 5 M3 Nylon insulating washers (to insulate PC tracks for some screws and spacers) 1 5mm LED bezel 1 20mm length of 5mm black plastic tubing (IRLED1 & IRLED3 1 70mm length of 5 x 0.75mm sheet brass or equivalent (rear panel support) 1 500mm length of red hookup wire 1 500mm length of black hookup wire 1 300mm length of yellow hookup wire 1 300mm length of green hookup wire 1 300mm length of blue hookup wire would be +1.5V, just below the 1.67V threshold. This means the IRD1 must detect a very strong signal in order to stay low long enough to trigger IC3. 1 600mm length of 0.8mm tinned copper wire (links) 29 PC stakes 3 50kΩ (503) horizontal trimpots (VR1,VR3,VR4) 1 10kΩ (103) horizontal trimpot (VR2) Semiconductors 2 IRLED receivers (IRD1-IRD2) (Jaycar ZD-1952 or equival­ent) 3 5mm infrared LEDs (IRLED1IRLED3) 6 555 timers (IC1-IC4,IC7,IC14) 2 4030 quad 2-input XOR gates (IC5,IC9) 1 4081 quad 2-input AND gate (IC6) 1 LM393 dual comparator (IC8) 2 4029 4-bit up/down counters (IC10,IC12) 2 4028 1-of-10 decoders (IC11,IC13) 16 3mm red LEDs (LEDs1-LED16) 1 5mm red flashing LED (LED17) 1 LM2940-T5 low dropout 5V regulator (REG1) 4 BC640 PNP transistors (Q2,Q3, Q10,Q11) 4 BC639 NPN transistors (Q4,Q5, Q12,Q13) 10 BC338 NPN transistors (Q1, Q6-Q9,Q14-Q17,Q18) 14 1N914, 1N4148 diodes (D1D14) Capacitors 1 2200µF 25VW PC electrolytic 2 470µF 25VW PC electrolytic 14 10µF 16VW PC electrolytic 4 1µF 16VW PC electrolytic 4 0.1µF MKT polyester 1 .039µF MKT polyester 1 .0033µF MKT polyester 1 330pF ceramic or MKT polyester Resistors (1%, 0.25W) 3 390kΩ 8 2.2kΩ 3 100kΩ 3 1kΩ 2 27kΩ 3 470Ω 3 22kΩ 4 56Ω 22 10kΩ 4 22Ω 1 3.3kΩ Miscellaneous Double-sided adhesive tape. The timeout period for IC3 is 2.9 seconds and this sets the reversing time for the robot. The triggering time is also signif­icant; it takes one September 1999  23 Table 2: Capacitor Codes  Value  0.1µF  .039µF  .0033µF  330pF IEC 104 393 332 331 EIA 100n 39n 3n3 330p tied high, pin 12 must be low for pin 11 to go high and so IC5a operates as an inverter. With pin 8 tied low, if pin 9 goes high, so will pin 10 and so IC5b operates as a buffer or non-inverter. IC5c is set up as a timer. When its pin 5 goes high, pin 6 stays low until the 10µF capacitor charges via the 10kΩ resistor. Thus the output goes high for this period then goes low. Similar­ly, when pin 5 input is taken low, the output goes high again until the 10µF capacitor discharges via the 10kΩ resistor. This output controls the motor speed voltage at pin 2 of comparator IC8a via diode D10. It does this by momentarily pulling the 1µF capacitor voltage high whenever the output of IC2 changes. Pulse width modulation Comparator IC8a provides the pulse width modulation signal to drive the right motor. It compares the speed voltage at its pin 2 with the triangle waveform at its pin 3. The triangle waveform is generated by 555 timer IC7, operating at around 400Hz. If the voltage at pin 2 is low, the resulting pulses from the output of IC8a will be high most of the time (ie, wide puls­es) and the motor will run at full speed. By pulling pin 2 of IC8a high whenever the output of IC2 changes we effectively stop the motor before applying a reverse voltage. Fig.6: this is the component overlay for board 2. Note that the IRLEDs and IR detectors will be angled to optimise collision avoidance. second for the timer to be triggered due to the 100kΩ resistor and 10µF capacitor time constant. The reverse timer is activated when the robot encounters a solid obstruction that it has not been able to avoid by simple steering manoeuvres. IRD2 and IC4 operate in the same way as IRD1 and IC2. IRD2 also triggers IC3 via diode D4. IC2 drives IC5a, IC5b & IC5c via diode D6. IC5a, IC5b and IC5c are 2-input exclusive OR (XOR) gates. The gate outputs only go high when one input is at a different logic level to the other. Thus, with pin 13 of IC5a Table 1: Resistor Colour Codes  No.    3    3    2    3  22    1    8    3    3    4    4 24  Silicon Chip Value 390kΩ 100kΩ 27kΩ 22kΩ 10kΩ 3.3kΩ 2.2kΩ 1kΩ 470Ω 56Ω 22Ω 4-Band Code (1%) orange white yellow brown brown black yellow brown red violet orange brown red red orange brown brown black orange brown orange orange red brown red red red brown brown black red brown yellow violet brown brown green blue black brown red red black brown 5-Band Code (1%) orange white black orange brown brown black black orange brown red violet black red brown red red black red brown brown black black red brown orange orange black brown brown red red black brown brown brown black black brown brown yellow violet black black brown green blue black gold brown red red black gold brown SMART FASTCHARGERS® 2 NEW MODELS WITH OPTIONS TO SUIT YOUR NEEDS & BUDGET Now with 240V AC + 12V DC operation PLUS fully automatic voltage detection Use these REFLEX® chargers for all your Nicads and NIMH batteries: Power tools  Torches  Radio equip.  Mobile phones  Video cameras  Field test instruments  RC models incl. indoor flight  Laptops  Photographic equip.  Toys  Others  Rugged, compact and very portable. Designed for maximum battery capacity and longest battery life. AVOIDS THE WELL KNOWN MEMORY EFFECT. SAVES MONEY & TIME: Restore most Nicads with memory effect to capacity. Recover batteries with very low remaining voltage. CHARGES VERY FAST plus ELIMINATES THE NEED TO DISCHARGE: charge standard batteries in minimum 3 min., max. 1 to 4 hrs, depending on mA/h rating. Partially empty batteries are just topped up. Batteries always remain cool; this increases the total battery life and also the battery’s reliability. DESIGNED AND MADE IN AUSTRALIA For a FREE, detailed technical description please Ph (03) 6492 1368; Fax (03) 6492 1329; or email smartfastchargers<at>bigpond.com 2567 Wilmot Rd., Devonport, TAS 7310 The oscilloscope waveforms of Fig.5 show the operation of IC8a. The lower trace is the triangle waveform at around 400Hz. This triangle waveform is compared with the voltage at pin 2, shown by the straight line. The output is the top trace which goes high whenever the triangle waveform is above the voltage at pin 2. The left motor circuitry, comprising IC9a, IC9b, IC9c and IC8b, operates in the same way as just described and IC8b is fed with the triangle waveform from IC7. IC6a and IC6b are AND gates which have the pulse signal connected to one of their inputs; they control the right motor H-bridge circuit, depending on the outputs from IC5b & IC5c. The H-bridge for the right motor comprises transistors Q2-Q9. When IC6a’s output is high, Q6 and Q9 are on and they turn on Q2 and Q5 which drive the motor in one direction while transistors Q3 & Q4 are off. When IC6b’s output goes high, Q7 & Q8 are turned on and they turn on Q3 and Q4 to drive the motor in the opposite direc­tion. The lefthand motor H-drive circuit is the same as for the right and uses transistors Q10-Q17 controlled by IC6c & IC6d. Both H-drive circuits are powered from the 6V supply reserved for the motor drive and they are each decoupled with 470µF capacitors to suppress the voltage spikes which can occur with the pulsing of the motors. LED17, a flashing LED, is connected across the battery supply to provide further visual activity. LED chasers The forward/reverse chaser comprises IC10, IC11 & IC14 and LEDs 1-8. IC14 is a 555 timer operating at •  RESELLER FOR MAJOR KIT RETAILERS •  PROTOTYPING EQUIPMENT •  CB RADIO SALES AND ACCESSORIES •  FULL ON-SITE SERVICE AND REPAIR FACILITIES •  LARGE RANGE OF ELECTRONIC DISPOSALS (COME IN AND BROWSE) Ph (03) 9723 3860 Fax (03) 9725 9443 Come In & See Our New Store M W OR A EL D IL C ER O M E Board 2 sits on top of the unit, while board 1 sits beneath it and forms the base of the chassis. Board 3 is mounted vertically, at the front. ELECTRONIC COMPONENTS & ACCESSORIES Truscott’s ELECTRONIC WORLD Pty Ltd ACN 069 935 397 27 The Mall, South Croydon, Vic 3136 email: truscott<at>acepia.net.au www.electronicworld.aus.as September 1999  25 Fig.7: this diagram shows the component layouts for boards 1 & 3. Take care to ensure that the correct part is used at each location. about 16Hz to clock IC10 which is a 4029 4-bit up/down counter. This has its pin 9 connected to ground to select binary coded decimal (BCD) mode so 26  Silicon Chip that it counts up to 10 only. The up/ down input at pin 10 connects to pin 3 of IC3 which goes high when the robot is in reverse. Thus, IC10 counts down when the robot is going forward and counts up when reversing. The 4-bit outputs from IC10 connect to IC11, the BCD-to-decimal decoder, and it drives the eight LEDs in sequence. Why only eight LEDs when IC11 has 10 outputs available? Well, we have to let the bean counters have their way on some occasions so they got to eliminate two LEDs! The turning chaser comprises counter IC12, decoder IC13 and LEDs 9-16. The circuit is very similar to the forward/reverse chaser but there are some differences incorporated to enable the LEDs to be switched off and also to ensure that during the chase sequence, at least one LED is always lit. IC14 clocks IC12 which is set up as a binary counter with pin 9 tied high. Thus IC12 counts in a binary sequence from 1-8 and we use only three out­puts. The Q4 output from IC4 is not connected but we play around with the D input (pin 11) of IC13 to make it do what we want. Taking the D input high prevents any of the eight LEDs from lighting. This is because a high D input represents a count beyond 8 and we are only decoding the first 8 counts; any count over 8 will not be decoded and the LEDs will be off. So the D input is pulled high by the two 10kΩ resistors associated with transistor Q18. Q18 is turned on via diode D12 or D13 when either the left or right motor timers (IC2 or IC4) have a high output at pin 3 and so pin 11 of IC13 is pulled low. This starts the LED chaser sequence, because the low D input means that the robot is turning left or right. The direction of the chaser depends on the voltage at the up/down input at pin 10 of IC12. It counts up whenever the right motor timer (IC2) output is high. In this case, the up count means a clockwise rotation of the chaser since the LEDs are in a circle. If Q18 is turned on via the left timer output, then the up/down input is low and the counter counts down and gives an anticlockwise direction for the chaser. If the reverse timer, IC3, has a high output, then the D input to IC13 is pulled high via diode D14 and the LEDs go out. Construction Autonomouse is built on three PC boards: Board 1 is coded 08409991 and measures 114 x 145mm; Board 2 is coded 08409992 and measures 114 x 128mm and board 3 is coded 08409993 and measures 114 x 72mm. A piece of double-sided PC board (114 x 69mm) forms the rear panel. Fig.8: these are the full-size etching patterns for boards 1 and 3. Check your boards carefully before installing any of the parts. The three PC boards and rear panel board are soldered to­gether to form the robot body. The front, top and a section of the rear are covered in red transparent Acrylic or Perspex to house the LED chasers and flasher and are mounted on tapped brass spacers. The 6V batteries each consist of a September 1999  27 This view shows how Autonomouse goes together. The motor/gearbox assembly is mounted on board 3 (details next month). Fig.9: actual size artwork for board 2. 28  Silicon Chip 4-AA cell holder and these are mounted on a platform panel measuring 75 x 110 x 2mm which attaches to board 1 on tapped spacers. The battery holders are held in place with double-sided adhesive tape. The two motor/gearbox sets are located on board 3. They are located with metal standoffs and held with brackets made from pieces of PC board measuring 35 x 20mm. You can start construction by checking the three PC boards for defects such as shorts or broken tracks. Repair these if necessary before assembly. Note that board 1 requires a couple of notches in its front edge nearest transistors Q4 & Q12. The shape of the notches is marked out in the copper pattern and is necessary to allow clearance for the screws for the spacers on board 3. Figs.6 & 7 show the component layouts for the three boards. Insert and solder in all the wire links and PC stakes on the three boards. The resistors can be installed next, and you can use Table 1 as a guide to the resistor colour codes. Next, install the ICs, taking care to mount each in its correct position and with the correct orientation. Trimpots VR3 & VR4 should be mounted on the copper side of board 1 to allow adjustment when the robot is assembled. VR1 & VR2 are mounted on the top side of board 2 in the normal manner. The transistors and diodes can follow, again taking care with their orientation; don’t get the BC338s, BD639s and BD640s mixed up. The capacitors can be mounted next and note that the elec­trolytic types must be placed with the polarity as shown. Table 2 shows the relevant capacitor codes. All the red LEDs should be mounted with their tops about 12mm above the board. This will allow clearance for the red acrylic which is supported on 15mm spacers. The three infrared LEDs are mounted at right angles to the PC board by bending their leads over in a gentle arc (not with pliers). The two infrared detectors, IRD1 & IRD2, are mounted with 1mm of lead protruding from the copper side of the PC board; don’t shorten their leads. That’s all we have room for this month. In Pt.2, we shall complete the construction and tell you how to test SC your Autonomouse.