Design Modular Planning

Transcription

1 Phys253 - Lecture 7, Part II Circuit Components & Layout Design Modular Planning Design by assembling simple circuit modules, such as filters or amplifiers Modules may be separated by buffers, where required Labs contain useful examples of modules 1

2 Design RC Tuning Resistor and capacitor values are only calibrated to within a few percent Where high precision: R/C matching is required, add a 10-turn trim potentiometer: Design Protecting Your HB Zener diodes prevent inputs from frying Handyboards Use a ~1 KΩ resistor to limit current & protect the Zener diode : Field Testing Without Zener Diodes 2

3 Design General Tips Place each important circuit on its own board, e.g. H-bridges - Makes swapping easy Run grounds from all power sources / circuits directly to a single point Layout Diagrams Layout diagram advantages: Circuits are easy to wire Circuits are consistently wired 3

4 What We See Layout What You See Note: Dramatization Layout - Printed Circuit Boards Can be cut to size on the sheet metal shear in the Student Shop. Ground Plane Side place all components & wires on this side Power Line Side - do all soldering on this side Look at trace width! Max ~2A on most traces, Max ~0.5A on header traces 4

5 Construction General Tips Soldering to PCBs Be Neat! Watch out for solder shorts Use sockets for IC s e.g. TL082 s MOSFETs Bad Good Construction - Wire Stranded wire for all flexible wires (careful with frayed wire can short to other components) Solid core wire for stationary wires on PCBs Multi-conductor Shielded wire for noise isolation Ribbon cable in place of multiple stranded wires, easy to make connectors (~1A max) Check the wire gauge rating for high-current lines (max for AWG ~1.5A) **TIP: solder wire to header pins instead of sticking bare wires to HandyBoard ** 5

6 Debugging by Modules Debug your circuits by modules Look at modules in order using the oscilloscope. Look at inputs & outputs of modules first do you see what you expect? Connectors & Cables Planning Loose connectors become an increasing problem as your robot becomes more complex Make connectors distinct wherever possible. Minimize # of 2 or 3- wire connectors gets confusing quickly. Label your connectors! Don t make cables absurdly long. ** TIP combine several wires into one large connector to HandyBoard (far easier to swap out HB) ** 6

7 Connectors in the lab Header pins polarize all your connections to prevent putting them in backwards or off by one position Molex terminals -for high-current connections Connectors not in lab Screw terminal block Speaker connections D-sub connectors Ribbon Cable Connectors Telephone jacks 7

8 Shrink Tube / Strain Relief Use shrink tubing around each solder joint from wire to pin/connector Strain relief all wiring leading off the PCB with a mechanical connection (e.g. tie-strap, another piece of wire, etc) Switches High-current toggle switch to: -block power to motors -block battery to electronics (better than pulling out connectors in a hurry!) DIP switches / Jumpers lead directly to digital inputs useful for controlling robot state, rather than using menu system. 8

9 Switches position sensing Microswitches are sensitive, but not mechanically strong don t do this. Optical Switch (QRD) Wall, edge, tape sense, non-contact block sensor Magnetic reed switch are good for non-contact detection 5 V Regulators used to get a steady 5V supply from a 7-15V supply 9

10 Shielding Noise avoidance sensitive circuits (IR detectors) Shield in a grounded box Amplify signals at the source. Send amplified signals to the Handyboard Standoffs To prevent your circuit board from shorting, keep it from touching the chassis of your bot. Cardboard or nylon bolts work great. Electrical tape doesn t. 10

11 Very different performance specifications for DC motors in lab Motors Geared Barber Coleman motor info (at 12V): 500 rpm no-load speed, 0.1A 30 oz-in stall torque, current = 1.5A Un-geared Barber Coleman motor info (at 12V): 7500 rpm no-load speed, 0.13A 6 oz-in stall torque, current = 2.5A ESCAP motor specs (at 12V): 60 rpm no-load 23 oz in stall torque, current = 0.17A Futaba Servo Motor S3003 operates just like servo-motor from lab (motor + built-in encoder), but all in one unit max 44 oz-in torque Instructions in Sec of IC Manual ** TIP: for max torque with Futaba, use external 5V supply ** Final Tips LABEL all important wires and signals. Use IC sockets for 8-pin components Protect back tab of Mosfets (back tab = drain) Use a SINGLE WIRE to separate IC s from the power rail for debugging Leave room for test-sockets on board for removing/inserting MOSFETS during H-Bridge testing Use external trimpots to analog inputs for tuning PID inputs. ** Optimize (e.g. desktop PC ), but don t over-optimize (e.g. laptop ) very difficult to repair/replace parts ** 11

12 Design Review Comments ~15-20 minute presentation, rest of hour for discussion Goal of all calculations convince us and yourself that your design will work as specified. Design for Ease of Use: Ease of assembly/dissassembly (HB, battery, fasteners) Ease of redesigning (i.e. leave room for improvement) Ease of fabrication (stock material vs. machining) Recognize the biggest risks/obstacles for your design during fabrication and operation. Design Review Comments S M Construction Time T W H F S Balance your time between incremental steps to completion ( test beds ) vs. fabricating only once for your final robot Time Trials Competition Take-Down 12