project prototyping - northeastern university college of ...jkimani/eece4790/project...

Project Prototyping

Project Prototypes

Prototype Definition: Initial Electrically Functioningmodel of a product which demonstrates primaryfunctions and modes

Good prototypes should; Be constructed in a durable and portable fashion Facilitate requirement verification Enable demonstration of operating modes and features Be integrated from functional blocks of all team members

Prototypes do NOT necessarily exhibit allfacets of mass production design andconstruction

Basic Prototype Methods

Breadboard or PlugboardAdvantages

– Solderless, Easy Mods– Very Rapid Prototyping– Well suited to TH 0.3” and 0.6” DIP IC’s & Low Power Discretes– Used in previous Labs

Disadvantages– Holes limited to #18-22 AWG “solid” leads/wires on 0.1” centers– Circuit must be transported with extreme care– Boards are subject to wearout, wire breakages, warping, etc– Expensive, cumbersome for larger circuits– Not suited to SMT, connectors, displays, power devices,

switches, etc– >10pF row-row capacitance

Breadboard Circuit

Image Source: https://tangentsoft.net/elec/breadboard.html

Breadboard Circuit

Image Source: http://electronics.stackexchange.com/questions/186974/breadboard-computer


Wirewrap or TermipointAdvantages

– Can be solderless or used in with solder– Relatively Rapid Prototyping– Well suited to DIP and SMT Conversions– Easy Mods but Very Reliable

Disadvantages– All parts must fit into WW sockets/headers on 0.1” centers– WW Wire is small, #30 AWG, <100mA, 250nH/ft– WW Tool and special solid WW Wire required– Best Results with Pre-stripped Wire– Requires special WW sockets, bottom ID’s and perf board

Wirewrap Circuit

Image Source: https://learn.sparkfun.com/tutorials/how-to-use-a-breadboard


Perfboard without PadsAdvantages

– Used with top or bottom side solder wire-wire connections– Can be used with DIP and SMT Conversion Sockets– Mods possible but require unsoldering– Reliable if used with hold down adhesives

Disadvantages– All parts must fit into sockets/headers on 0.1” center hole

pattern– Solder connections made with wire-wire or wire-pin– Insulation on wire connections can be compromised with heat– Slower than Wirewrap or solderless breadboard– Requires higher degree of soldering skills


Perfboard with PadsAdvantages

– Used with top or bottom side solder wire-wire connections– Can be used with DIP and SMT Conversion Sockets– Mods possible but require unsoldering pads (vacuum required)– Available with Gnd Planes, Power Traces/Busses– Better solder connections than w/o pads, More Reliable

Disadvantages– All parts must fit into mountings on the hole pattern– More expensive than std perfboard– Slower than Wirewrap or solderless breadboard– Requires moderate degree of soldering skills

Perfboard with Pads

Image Source: http://dos4ever.com/uTracerlog/tubetester.html

The µTracer, a miniatureTube Curve Tracer /Tester

Perfboard with Pads

Image Source: https://en.wikibooks.org/wiki/Practical_Electronics/perfboard

Perfboard with Pads

Image Source: http://forum.arduino.cc/index.php?topic=111021.0


Deadbug BoardAdvantages

– Access to connection side of all parts– Allows an excellent ground plane(s), Great for HF, VHF, UHF, RF– Copper board can be scraped to provide power traces as well– Inexpensive, Reliable if used with hold down adhesives

Disadvantages– Part markings are upside-down– Not suited to digital or nodal intensive circuits– Requires adhesive to “deadbug” parts– Slow Method, Can be very delicate when part legs extend vertically– Requires very high degree of soldering skills

Deadbug Board

Image Source: http://www.freestompboxes.org/viewtopic.php?f=20&t=16902

Deadbug Board

Image Source: http://kd1jv.qrpradio.com/ap80/AP_80_ugly.jpg


CNC Routing Circuit BoardAdvantages

– Access to connection side of allparts

– Allows a single ground plane(s),Great for power supply, RF

– Can be std 62.5mil, 93mil, 125 mil or thicker board if needed– Immediate Turn Around

Disadvantages– Limited to single and double sided boards– Limited component density, thru-hole & 1st generation SMT– Must use compatible CAD tool to generate artwork

CNC Routing Circuit Board

Image Source: http://buildsmartrobots.ning.com/profiles/blogs/pcb-isolation-milling


Printed Circuit Board – PCBOutsourcedAdvantages

– Professional, repeatable performance for RLC, mass producible– Can be used with or without component sockets, SMT or Thru Hole

Parts– Fast assembly once PCB is procured– High current capability for any conductor– By far the most reliable prototype method– Circuit can be matched by computer to intended schematic

Disadvantages– Procurement Time of PCB Fab takes ~1-2 weeks, (quick turn is an

option)– Changes or mistake fixing can require “unsoldering” skills/tools– Extra Design Task of Creating Board Layout File/Artwork

Printed Circuit Board – PCB

•ExpressPCB - Full schematic capture and PCBlayout•Pad2Pad Custom PCBs - Layout package andordering•CadSoft EAGLE PCB Design Software -Schematic and layout editor•DesignSpark PCB - Schematic and layout editor

Total Nodes

Temp Sensor Circuit

• 3 ICs: LM35 SO8, OP07 Dip 8

• 6 Capacitors: Ceramic MonolithicAxial

• 4 Resistors: 0.125W Axial

Designing PCB

Device

NumberMfg PartNumber

Description Qty Package

U1 LM35DCN Precision Temp Sensor 1 SO8

U2,3 OP07CP Low Noise Bipolar OpAmp 2 DIP8

R1-4 10K, 1%, 1/4W Metal Film Res 4 Axial2

C1-6 0.1uF, 50V, 20%, Ceramic Mono Capacitor 6 Axial2

Bill of Materials Example for Thermal Sensor Circuit

Circuit Layout

PCB Board

10 Guidelines

1. Make good power supply and ground connections A 30 AWG#, daisy-chained wire-wrap connection from chip to chip is very

inadequate. For similar reasons to the decoupling, you must make low impedancepower supply and ground returns.

For single and double sided boards use 20mil or larger (wider) traces. For multilayer boards use separate planes for power(s) and ground(s) when

possible Check ALL wire & trace gauges for proper current capacity.

2. Decouple ALL IC power inputs This includes analog, digital and data conversion IC’s Employ a 0.1 uf ceramic capacitor from each supply to ground as close to the IC

as possible. Switching internal to the IC can cause momentary voltage drops dueto package and line length inductances. A local capacitor helps counteract thiseffect by providing local energy.

Include separate bypass capacitors for both the positive and negative supplies Each circuit board should have additional “bulk” capacitors such as solid tantalum

depending on local current draw

10 Guidelines

3. Keep digital and analog circuitry physically separated if possible Digital switching, especially at microprocessor bus or video card speeds, can

inject switching noise and other unwanted effects into analog circuitry. When possible use separate analog and digital power and ground return runs,

planes and/or wiring back to a central point as close to the DC power source aspossible. This will keep the digital noise out of the analog circuitry.

4. Assume you may need to make changes! Choose a suitable prototyping method that allow for changes, leave yourself

enough space on your boards

5. Account for ALL your pins! Terminate all unused inputs in some fashion which allows them to be utilized if

needed without substantial rework. For example, spare op-amps can beterminated by creating unity gain followers and grounding the input.

Do NOT leave unused input floating unless the device is specifically designed forthis condition.

10 Guidelines6. Make sure your parts are available before locking in your design

7. Construct in circuit blocks Construct and test functional blocks verifying performance as you go. Do NOT

assemble more than a few blocks at a time before verifying functionality. Themore circuits that are assembled and integrated, the harder it is to debug.

Whenever powering up circuitry the first time, ALWAYS check the DC supplycurrent as the circuit powers up with your hand on the ON/OFF switch. If there isa wiring or connection mistake, many times it shows up as an over currentscenario. Be ready to turn off the supply in the event of an overcurrent.

8. Cleanliness of circuits is essential for low signal analog performance Don't use silicon sealant to tie down high-impedance or low current analog circuits!

It may leave ionic laiden residue that can leak small currents which may bedetrimental to circuit performance.

9. Use IC sockets on prototypes along with Thru-Hole technology if possible. The “product” design can be very different in its packaging technology. Do NOT

assume you need to use the same IC packages in your prototype.

10. Treat the PCB and other interconnect systems as part of the circuit design. All PCB’s, wiring, breadboards, etc have resistance, capacitance and inductance

Soldering

Solder Pump Removal ToolNote: Some Solders Contain LeadAlways Wash Hands AfterContacting!

Best Practice•ESD and heat protective lab bench top

• Heated Soldering tool (25W min iron) with small tip forelectronic work

• Adequate ventilation

• Safety glasses and other protective clothing/equipment

• Small gauge #18AWG or smaller Sn63Pb37 rosin coresolder wire

• De-soldering tool (wire braid or suction tool)

Easy to see the difference between good-badsolder joints

Bad (COLD) Solder JointsGood Solder Joint

SMT to TH Adapters

• SMT IC’s may need to be converted to Thru-Hole in order for prototyping

• Useful adapters are available as shown below; www.arieselec.com/products/correct.htm www.beldynsys.com

TSSOP32 to DIP32 AdapterPQFP44 to DIP44Adapter

SocketPLCC44 to DIP44 Adapter

QFP80 to PGA80AdapterPLCC20 to DIP20 AdapterSOL16 to DIP16 Adapter

Plan the Project Prototype

1. Partition the Electronics, Determine # of Circuit BdsConsiderations

– Annotated block diagram showing mapping of blocks to boards– Functional Separations, Block Separations, Displays & User

I/O– Power Supply or Safety Circuits from Analog or Digital– EMC and ESD protections, RF Circuits and Shielding– Power and Heat Dissipation, Heat Sinks, Fans, Cooling– Battery attachments and compartments– Total path length and “inductance” from power source(s)– Total surface area of components

2. For each design block, determine:– Footprint area for or each unique part including mounting– Total area of design block prototype parts– Total area required for each circuit board (min 5X part area)

3. For each circuit board, select the type(s) of substrates& mfg– Printed Circuit Board

• Outsourced• Handmade Transfer• Handmade Photo-Litho

– Pre-Perforated Boards• Plastic, no pads, no busses• Plastic, pads, no busses• Plastic, pads, busses

– Flat Insulating Substrate– Bread Board– Other

Project Prototyping Plan

http://www.minute-man.com/acatalog/Online_Catalog_Prototyping_Printed_Circuit_Boards_and_Materials_246.html

http://www.radioshack.com/


4. Determine the type(s) of component attach– Direct Solder or IC Socket

• For Cu PCB or Perf Boards• Adapters for SMT

– Wirewrap Socket• For Cu PCB or Perf Boards

– Deadbug– Other Mechanical


5. Determine the type(s) of interconnection, toolsrequired per board

– Solid Wire Solder Connection• Use #18-22AWG for power• Solder all connections

– Wirewrap #30 AWG• For small signal connections• Less than 25 mA• No Soldering Necessary

6. Determine the type(s) of interboard connections– Parallel or Buss Connections

• Ribbon Cable, Headers– Power Connectors

• NEC, IEC320, DC, Molex– Individual Signal Connectors

• Audio: RCA, Motorola• Video, RF: BNC, F, N, S, SMA/B• Telecom: Sub-D, RJ-11, RJ45, USB



7. Determine the overall enclosure types and numbers;– Metal Enclosures (Provide Shielding, Grounding)– Plastic Enclosures (Provide Durability, Workability, Impact

Resistance, Insulation, Matched with Displays)• Both are available in numerous off-the-shelf products http://www.vectorelect.com/

project prototyping - northeastern university college of ...jkimani/eece4790/project...

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