11 Hand-Made Prototype PCB Guide

 

Laser printouts

·        Top layer — Holes (vias), top copper, outline only

·        Bottom layer — Mirrored Holes (vias), bottom copper, and outline

·        Laser printer (select highest dpi)

·        Take printouts only on Photo papers (for a better-quality heat transfer), magazine laminated papers shall be used

Equipment

·        Fr4 copper board

·        Dry iron without water vapor

·        Surgical sprite or any liquid alcohol

·        Stain removing chemical (Brasso) or sandpaper

·        Low humidity room (for better results)

·        Thin metal single-core wires for aligning (0.5mm gage) — alternatives — metal wire of resistors or 0.3mm gauge coil wires

·        Double side PCB — vias — 0.7mm coil wires (coating should be removed cleaned)

·        Hand drill — Dremel and drill

·        drill bits 0.3mm /0.7mm

Process

·        Cut the required size of copper board

·        Clean the copper board both sides using Brasso, all the stains should be removed

·        Cut laser printed photo paper

·        Clean the copper board with alcohol before start heat transfer, before pacing printout on copper board

·        Take a printout of one side only (prefer top side first)

·        Place laser printout on copper board

·        Heat transfer should be started immediately after taking the printout — otherwise, the humidity will damage the quality of the heat transfer process

·        Heat transfer for 10min 15min

·        During ironing do not pat photo paper to slip or move on the copper board, hold it until it gets to stick with the PCB board

·        Heat transferring more than 15 min will damage the printout — damages transferred tonner — damages copper paths in the PCB board

·        Clean the PCB — use water to wet the sticked photo paper, use a smooth brush to the pill of the paper, do this carefully otherwise tonner will come off from the PCB board

·        Small tonner damaged areas can be repaired with a permeant marker- not recommended for complex PCBs with many damaged areas — redo the process if you have messed up

·        For double-sided PCBs — make 3 holes (0.5mm/ 0.3mm or less) for aligning if holes are bigger the PCB will misalign — go for random places on PCB — ( eg- not square- random places will align the PCB properly)

·        Take a printout of the other side (mirrored bottom side)

·        Place bottom side mirrored print out on the other side of the copper board

·        Make the same three holes on bottom side printout

·        Use 0.3mm/0.5mm metal wires for aligning

·        Heat transfer for 10min 15min

·        Do not let PCB boardslide on the surface, transferred tonner on the other side (top side layout) will damage

·        Clean the PCB — use water to wet the sticked photo paper, use a smooth bush to peel off the wet photo paper, do this carefully otherwise tonner will come off from the PCB board

·        Use ferric chloride for etching — hot water — speedups the process

·        Room temperature water also fine

·        Use ferric chloride powder- this speed up the process

·        Don’t use stiffed ferric chloride — it is not soluble in water

·        Don’t breathe the smoke comes during the etching process — this is harmful chlorine gas

·        Once all the unwanted copper is etched PCB is ready for soldering.

 

10 Importance of floating bus voltage for current sensing

 

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Importance of the floating bus voltage for current sensing

This is used in high voltage >100V, high side current sensing applications

For some application 400V common the mode is prepared but ic available on market will support only somewhere around 100V, but the circuit can be modified slightly to support them to 400V, its called a floating supply voltage to the current sensor where the current sensor is not referred to GND but supply rails are between supported voltage, this is done but using Zenor diode which will float supply rail of the current sensor between 400V and 395V if 5V Zenor is used.

The following reference is from Texas instruments

Rail-to-rail opamp OPA333 used to mirror the sense voltage across the shunt resistor on a precision resistor R1.

OPA333 is mirroring the sense of the voltage across Rshunt to the R2

The opa333 is floated up to 400V by Zener diode, so the OPA333 is not referred to as the GND, it sits somewhere between 395V to 400V so supply rail difference is 5.1V, also inputs are not referred to the GND in this circuit.

The 600V P-Fet is used to perform the current following where the gate is controlled by OPA333, the P-Fetis never fully turned on, gate voltage will be adjusted by opa333 precisely to mirror the Vshunt across R2.

The voltage across R1 sets the drain a current of the FET and by matching the resistor R2 in the drain of the FET to be equal to R1, VSENSE voltage is developed across R2 (VR2).

Additional INA226 is not also on 400V, so it does not need higher common-mode voltage, voltage divider has used to drop 400V to INA226,

INA226 measure only 100mV across the R2

9 Instrumentation Amplifier Selection Guide

 

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IA selection guide

IA — Instrumentation Amplifier

CMRR — should be higher, this will suppress common-mode unwanted signals

The low input bias current

Low drift

Low input voltage offset

Low input voltage noise

Slew rate —select according to application

Supply voltage range — rail to rail range, single-supply range

Gain bandwidth — select according to gain and bandwidth requirements of the application

Input impedance — this is usually higher than general op-amps

Low input current noise

Price — high precision IAs are very expensive, be aware of the application requirements against the required IA specifications

Package size

PCB layout guidelines- usually provide in datasheet or application notes

8 BLE Application Data Rate

 

BLE Application Data Rate

Is it 1Mbps as you can find on the net? No, Typically bandwidth is defined as the whole bits of the frame per second. In other words it the raw bit rate, user data + packet payload

The actual maximum user data rate will be 0.27Mbps, this is also with only a few devices, it changes depends on manufacture and OS as well, so be careful when doing rate calculation for your project when using any sort of wireless communication

Manufacturers mention only bandwidth which misleading Starters !!!

When to use BLE?

BLE shall be used for a short burst data advertising, where especially lower power consumption is considered

 

7 Usage of Electronic Reference Designs

 

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Usage of Electronic Reference Designs

The following sites contain tons of reference designs where an electronic designer could replicate design ideas easily rather than design from scratch, at the same time it will increase design skills asl well.

Reference designs will accelerate designing and designer does not have to read datasheet deeply

Reference designs are opensource as well.

3rd party manufacturers

• Adafruit
• Spark fun
• Groove
• Seeed studio
• Mikroe click boards
• Cjmcu.com
• Tindie
• Hockaday

Evaluation modules from the manufacture

• Texas instruments
• Analog devices, linear technology
• Maxim integrated
• Renesas
• Microchip
• St microelectronics

Optional

• Bangood
• Farnell
• Amazon

6 Lipo Fast Charging Current

 

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• If no charge rate is defined in the battery, (mostly unbranded batteries )then C/2 is safe…
• If 1000mAh (1Ah)/ 35C(discharge) battery/ 3.7V/ no charge rate is defined, Then charge at 500mA is safe.
• If 1000mAh (1Ah)/ 2C battery/ 3.7V, Then charge current max 2A (1A x 2C).
• If 5000mAh (5Ah)/ 3C battery/ 7.4V, Then charge current max 15A (5A x 3C).

5. Importance of DC to DC Converter Efficiency

 

If you are doing amps simulations you will find SMPS having 40%, efficiency over 70% or 85%

Higher the better !!!

why this efficiency matters?

40% efficiency — It’ll get hot, and waste heat.

What about output voltage? will it be floating?

Efficiency and stability aren’t necessarily related.

Will lower efficiency booster burn out due to its heating?

it depends. For every 1 watt you put in, you’ll get out 400mW, and 600mW will get burnt up as heat. If your booster’s thermal design isn’t up to handling that heat with proper thermal spreading or heat sinks, it’ll get too hot and burn up.

Also, the main disadvantage of low efficiency is energy loss

A with low efficiency may also produce more EMI due to the higher current it requires. This may affect other circuits as well

2. Designing Custom Fly back Based On TI Design Tools

 

source — fuiji electric

Designing custom flyback based on TI design tools

• Perform TI simulation web bench — web bench is not capable of providing transformer spec most of the time, but it will provide tech details
• Select a suitable ic
• Use TI selected IC’s design tool .xlx file
• Recalculate circuit spec
• Find a suitable transformer supplier — based on inductance/i peak/ input-output voltage/ frequency
• If standard/premade transformers are not available, the transformer has to be custom made

General guide

• Switch Mode Power Supply Topologies Compared
• Fly-back transformer design instructions

3. Why Digikey is the best choice for mass production component searching?

 

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Once you are done with prototyping,

How to reduce the cost of mass production?

Where to search for alternative components?

How to find alternative components to reduce PCB size?

Digikey Pros

• Digikey has 99.99% of the components from worldwide manufactures
• Digikey has all technical data listed
• Digikey has all pricing types this is useful for mass production
• Offers the lowest price for mass production
• Quick delivery worldwide
• Quality products — no Chinese replicas

Digikey Cons

• Digikey does not have 3rd party testing modules as in eBay and Aliexpress.
• Only has manufacturer evaluation boards which very expensive

Other Sites For Quality Products

• Arrow
• LCSC electronics
• Farnell
• RS component
• Tindie
• Mouser
• Amazon

4. Ki CAD Assembly Drawing Design Tips

 

Finalized Assembly Drawing PCB House-Top

 Finalized Assembly Drawing PCB House-Button

  

Download Libs from snap EDA or Ultralibrarian

Edit footprints

• Fab layer — ref designators %R
• Height 0.5mm
• Width 0.5mm
• Thickness 0.15mm
• Fab layer outline of the component
• Delete existing fab layer — hard to see in print format
• Draw in Fab layer on top of cortyad
• Keep fab layer designator inside the fab layer outline

Fab layer important

• Led cathode
• Diode cathode
• IC pin no 1
• Pin header pin no 1
• Multi-pin connecter pin no 1
• Electrolyte capacitor cathode
• Led cathode
• Etc..

Silkscreen designator is not must for mass production or for PCB house