Robot Electrical & Mechanical Block Diagram

Transcription

1 Robot Electrical & Mechanical Block Diagram loudspeaker (output) 100 ufd cap. 5V G Basic Stamp II OEM Kit ( wires f wheelcontrol signals Programming cable detach to run serial cable to serial pt (Windows) OR Keyspan USBtoSerial converter to USB pt (Mac Windows) holder "mot" 4 AA cells 6 volts 6V G L298 Hbridge board (custom) 9V G "logic" 9 volt holder set screws hub wheel plastic bearing axle shaft coupler left mot wheel & drive components right mot wheel direct drive alternative The Block Diagram This block diagram is to help explain the electrical system of your robot. It should also help in planning the physical size of your robot to make sure everything fits. This drawing is not to scale however, so be sure and lay out the actual parts on the body and trace them befe you start cutting any materials. Below is a list of some of the maj components with a very brief explanation of how they wk. Parallax Basic Stamp II OEM Kit: This is a small computer (referred to as a microcontroller in industry) that has 16 pins, which can be programmed to act as inputs (and read senss) as outputs (and drive mots loudspeakers). Our Basic Stamps come in kit fm and we will build them together in class. The Basic Stamp is, logically enough, programmed in the BASIC programming language. You may download the programming environment f free at and program your robot at home. You will need a serial cable and a PC with a serial pt, a Keyspan USB adapter if you have a Mac. After the B.S. is programmed, the cable can be detached and the Stamp will run the program on its own, as soon as the power is applied. L298 HBridge Board: The Basic Stamp alone is not able to provide enough current (electron flow) to drive the mots of our robots. The L298 is a specialized integrated circuit (IC) that is engineered f this job. It takes signals from the computer and outputs high current mot signals to start, stop and turn the robot. (Only one wheel activated creates a turn, f example.) The L298 board also has some convenient features such as switches to turn on off the mots and Basic Stamp and some pilot lights to tell when things are turned on and wking properly. It acts as the main power controller f the robot. Senss: We will primarily use two types of senss on our robots. Bump sens which look like wire whiskers, and photocell s which look like small buttons attached to wires. Both are simple to hookup and can be used to generate a surprising number of behavis. Toward the end of class, interested students may wish to try to hook up some other senss with parts available online at Radio Shack. Loudspeaker: The loudspeakers can produce a fairly low volume melodies and sound effects that can be programmed into the Basic Stamps. It can be made louder with the addition of a one transist amplifier, a special amplifier IC. Our computes/loudspeaker cannot reproduce sound files sampled sounds. We can however hook up voice chips talking pictureframe type devices to accomplish this task under the controll of our robots. s s light emitting diodes are small light emitting devices that can be used on robots to signal behavi states, help debug software, just f fun and artistic effects such as light up eyes in an animalrobot. Students should have four each of red, green and yellow in their kits. In

2 Connecting the Hbridge board to the computer BASIC Stamp 2 OEM mot connects solder joints VDD VSS VIN RES P6 P7 P8 P hot glue to reinfce solder joint. header pins inserted into breadboard mot wires to 6V "mot" to 9V "logic" to left mot to right mot The Hbridge input lines A1 & A2 control the left mot and lines B1 & B2 control the right mot. If you trace the lines to the Basic Stamp you will see that they are controlled by pins 1&2 and 3&4 respectively. What this means is that ifzzzz you want to turn both mots on to make your bot move fward you need to make pins 1 and 3 of the Basic Stamp high. Incidentally, what we will refer to it as logic 1 high is really 5 volts. The opposite concept is low which we will also refer to as logic 0, 0 volts and ground. Below is a chart, sometimes referred to as a truth table that shows how to make your robot move by controlling the pins of the Basic Stamp. Note that pins 0 & 3 are labelled Enable. These pins, if used, will turn on and off the mots no matter what other direction the mot pins are set f. F the sake of clarity, and easier programming, we will not use these pins at first, so the numbers filled in f pins 0 & 3 will just be zero. Mot control logic ' Mot test program Enable left wheel A1 A2 Enable B1 B2 right wheel Direction B.S. Command use f general purposes dirs = % fward outs = % backward outs = % braked stop outs = % coast stop outs = % soft left outs = % soft right outs = % hard left outs = % hard right outs = % use f speed control dirs = % fward, etc. outs = % x x 0 x x coast stop outs = % ' Lines with single quotes " ' " are comments ' They don't do anything, but make program me readable ' Use lots of comments to explain how your program wks ' Begin program here dirs = % 'percent sign means number is binary ' makes pins 1,2,4,5 outputs; 0,3 inputs 'the colon means "" is an address label outs = % 'set pins 1,4 "high" robot moves fward 'if it doesn't swap mot wires pause 2000 'pause 2000 milliseconds (2 seconds) 'the computer pauses but the robot keeps going 'because the mots are turned on outs = % pause 2000 'set pins 2,5 "high" go backward 'pause 2000 milliseconds (2 seconds) outs = % 'soft left turn because only right mot is on pause 2000 'pause 2000 milliseconds (2 seconds)

3 L 2 L298 Hbridge board 2 header pins 6 header pins note stripes on is positive Note capacit and polarities note stripes on diodes (8 places) red wire black wire to mot batteries 4 "AA" batteries 6 volts 1N400x 2 header pins Assembly instructions to 9 volt "logic " General Ideas: Solder in resists, diodes, smaller parts first, switches, IC and header pins last. Be sure to observe polarities on electrolytic capactis, diodes, s. StepByStep: small switch red wire First solder in 6, 10k resists (brownblackange) and 2, 2k resists (redblackred). Solder in 8, 400x diodes. These are polarity sensitive so be sure you get the stripe going in the direction shown in the image above (stripe facing up). Install 2,.1 ufd capacits (they will be marked 104), these are not polarized. Install the 1 ufd capacit and the two 100 ufd capacits. These are polarized and must be inserted the right way. The s are positive and the negative side is marked on the capacits. Solder in the two s. The is positive which is marked on the board. Install the two slide switches. The leads on the larger one neede to be bent carefully with thin nosed pliers. This will be covered in class. Install the header pins. Inserting them into the breadboard first will make soldering them easier. Note that the mot connects need to be intstalled on the TOP of the board. black wire 2 header pins, 2 places solder on TOP side of board Parts List Semiconducts 1 L298 Hbridge voltage regulat 8 1N400x diodes 2 's different cols Resists 2 2 k 1/4 watt resist 6 10 k 1/4 watt resist Capacits 2.1 ufd 25 volt monolythic capacits 1 1 ufd 25 volt mono. tant. capacit ufd 25 volt electrolytic capacit Hardware 1 large SPDT switch Jameco CK 1 small SPDT switch Jameco CK 1 14 header pins 1 4 cell C AA holder 1 9V holder Solder in the L298 chip. Hook up the wires to your holders. Make sure you get the red wires hooked up to the positive "pads" on the board. Now you are ready to test your Hbridge board.

4 L298 Hbridge board, thesting and they of connect Testing the board 5V L298 Hbridge board The mots must be connected to test your Hbridge board. Please see page 2 on how to construct the mot connects. To test your Hbridge board, insert your batteries and briefly turn on your switches. The pilot lights should light. If they do not, turn off the switches immediately and take a out of each holder. Ask f help in troubleshooting your circuit. If the s wk, clip a jumper lead to the 5 pin of the header, taking care not to also touch the ground lead (and shting the circuit.) Now touch the logic leads one at a time. If all is well when you touch the A1, and B1 leads the mots will run in a fward direction, and when you touch the A2, and B2 leads the mots will run in a reverse direction. If this is not the case then just reverse the connect to the mot that is wking in the opposite direction that it should. If the mots do not run at all run very slowly, you have a problem with your board, and should ask f help in troubleshooting. & Hbridge they 98 DC (direct current) mots will reverse if the polarity of the electrical supplies is reversed, as in Figure 1. There are several ways to do this conveniently. One way is with a switch that can switch two wires at the same time. This is called a doublepole, doublethrow switch, as shown in Figure 2. It is possible to automate one of these switches with an electromagnet. This would be called a relay, specifically a DPDT relay. However this still involves a mechanical switch which is prone to failure, so solidstate (transistized) methods have been invented to do the wire switching. Figure 3 is a much simplified diagram of this scheme, which is called an Hbridge. The geometry of the circuit diagram is where the Hbridge gets its name. It requres four switching elements. In this drawing the schematic symbol f switches have been used but in practice these would be either transists MOSFETs (a special kind of transist). When control 1 is activated, switches 1 and 3 close and the mot rotates in a fward direction. When control B is activated, switches 2 and 4 close, the mot rotates in the reverse direction. Note that control lines 1 and 2 can never be activated at the same time power will flow directly from positive to negative creating a sht circuit. Your L298 integrated circuit contains two separate Hbridge circuits. Each circuit has the control lines 1 and 2. There is some logic circuity that insures that the switches aren t turned on at the same time, even if the control lines are activated. There is also an Enable control not shown in this diagram. It turns off the power to the whole circuit, which lets the mot coast to a stop. V F Off R Figre 2: A DoublePole DoubleThrow (DPDT) switch wired as an onoffreverse mot controller Control 1 Fward Figure 1 S1 V (positive) S2 Reverse Control 2 S4 S3 (Ground, negative) Figure 3: A simplified schematic of an Hbridge

5 Connecting senss to the Basic Stamp computer BASIC Stamp 2 OEM 5 V 10k resists springs music wire pullup resist 10k bump switch Vss Vdd Vin RES P6 P7 P8 P schematic diagram The Hbridge and mots are not shown here f clarity. solder 103 is positive on.01 ufd capacit photocell Wiring two es Pins 14 and 15 which are connected to the springs and are also connected to two, 10k resists. These resists are called "pulldown" resists because they make sure that the pins are kept "low" (at ground) until the switches are activated. When the wire of the gets pushed hard enough, it will contact the sping. This connects the spring (which is also connected to the ) to 5 volts. Now the voltage at the pin is "high" (5 volts). To add me es just duplicate this setup. 'Basic Stamp code fragment of how to read switches IF IN15 = 1 THEN gosub BackUpAndTurnLeft 'these addresses would need ELSEIF IN14 = 1 THEN gosub BackUpAndTurnRight 'to be defined below ENDIF 470 ( standard) schematic diagram 5 V.01 ufd capacit 100 pfd omit entirely f phototransist phototransist Wiring an When the pin is made an output, and also made high, there is 5 volts present at the pin and current flows through the. The resist is necessary because 's won't limit current on their own and will burn themselves ( the B.S.) out if installed without a resist. The particular resist used determines the current through the, in this case about 2.5 milliamps. If you want slightly brighter 's then use 470 resists (yellowvioletbrown) but they will drain your 9 volt faster. Duplicate circuit f me 's. Each needs its own resist. 'Program Blink con 6 '"" is a constant, defined as 6 'using constants makes programs easier 'to read, and the hardware easier to change 'if you need to switch pins high 'the "high" command makes the pin (pin 6 in 'this case) an output and makes it high (5) pause 1000 'computer pauses 1 second stays on low 'turn the off pause 1000 'pause 1 second RCTime schematic diagram Reading a Photocell with RCTime RCTime is used to read a photocell other sens that acts like a resist (such as a potentiometer thermist). It measures the time it takes to charge a capacit through the sens, which is proptionate to the sens's resistance. 'Basic Stamp code RCTime rcpin con 10 'change "10" to the pin used result var wd HIGH rcpin ' discharge the cap PAUSE 1 ' wait 1 ms f cap to discharge RCTIME rcpin, 1, result ' measure RC charge time DEBUG DEC? result ' display result goto main goto main 'do it again