PCB Know How

Generic Standard on PCB Design (IPC2221A)

PCB

Rigid Laminate material (FR4, typically) consisting of a glass epoxy substrate clad with copper on two sides for double sides (0.062” typically)

PCB fabrication Gerber data requirement

1   1) Top Electric (Artwork)

2   2)    Bottom Electric (Artwork)

3   3)    Top Silk (Artwork)

4   4)    Top Resist (Artwork)

5   5)    Plated Through Hole (N.C Drill)

6   6)    Non-Plated Through Hole (N.C Drill)

7   7)    Board Outline (Artwork)

8   8)    Drill Table

    Electrical Clearance

    AC and pulsed voltage > 200V must consider the dielectric and capacitive effect of the substrate in addition to spacing.

     

     Minimum spacing requirements according to withstand voltage are as below

Withstand Voltage (V)	Minimum Spacing (mil)
0 ~ 30	3.9
31 ~ 150	24.0
151 ~ 300	49.2
301 ~ 500	98.4

Electrical Isolation (Creepage Vs Clearance)

     Creepage is the shortest path between two conductive parts measured along the surface of the insulation. Clearance is the shortest distance between two conductive parts measured through air.

     Copper Weight

     1 oz of copper will cover one square foot area when rolled out to a thickness of 0.0014 inch or 1.4 mil.

Copper Weight (oz)	Thickness (inch)
½	0.0007
1	0.0012 ~ 0.0014
2	0.0028

     PCB Surface Finishing

     Different types of PCB finishing are as below

     1)    Hot Air Solder Level (HAL or HASL)

     2)    Hard Gold-Electro plated gold

     3)    Electro Less Nickel Emersion gold

     4)    White Tin

     5)    Organic Solderable Preservative (OSP)

     

     The most common surface finishing we can see is Hot Air Solder Leveling. In this process, Panels are processed through a bath of molten solder, conversing all exposed metal surfaces. High-pressure hot air, directed at both sides of the panel simultaneously, removes excess solder from the holes and surfaces.

     PCB Trace Width vs. Current Table

       A PCB trace width vs. current table helps you understand the relationship between PCB trace width and current carrying capacity so you can determine the required trace width for your printed circuit board design.

Microphone Pre-amp

Low Noise Microphone Preamplifier Circuit

R1, R2, R3, R4 & R8: Low excess noise metal Film

C1, C2 & C3: Input and output coupling

C4 : Noise filter, C5: bypass

NOTE: Input Cable to microphone must be shielded

Relay Circuits

Momentary Relay Activation Circuit

The relay will energize momentarily until the capacitor is fully (or partially) charged.

Protection Diodes for Relays

The relay coil produces brief high-voltage spikes when switched off. These voltage spikes can destroy transistors and ICs in the circuit. To prevent damage, a protection diode must be placed across the relay.

Controlling Multiple LEDs

Multiple LED Control Using Minimum I/O pins



A truth table for controlling six LEDs using three I/O is shown below:

H = Output Set high (5V)

L = Output set low (ground)

I = Input

More LEDs can be controlled by using this equation:

Numbers of LEDs = (Numbers of PINs) x ( Numbers of PINs – 1)

For example:

Number of LEDs = 4 x (4-1)

                        = 4 x 3

                        = 12 LEDs

Speaker Volume Control Circuits

Speaker Circuit with Adjustable Volume Control



This is how we usually build an 8/4/16 Ohm speaker with adjustable Volume Control. It can handle up to 15W speakers without any issues.

100V Line Audio Volume Control with Bypass Option

This is a 100V line speaker volume control with an Emergency bypass. It requires DC 24V to bypass the audio level control.

Buzzer Control

Simple Buzzer Control Circuit



This is a simple buzzer control circuit with one resistor and  FET. The circuit is suitable for magnetic buzzer indicators.

DC Motor/ Fan Monitoring

DC Motor/ Fan Failure Detection Circuit

It is essential to monitor the health status of fans in some systems to ensure that cooling fans are operating reliably and efficiently. This helps prevent damage to sensitive components and equipment.

Explanation of How the Circuit Works:

Rsense acts as a Fan Current Sensing Resistor with a high power of 30.1W. R1 and C1 establish an average DC level at the midpoint of the transistor of the current waveform and apply this voltage to the base of Q1. Silicon NPN transistors are suitable for Q1.

This DC motor/fan failure detector is designed to detect fluctuations in current through Rsense. It promptly triggers a high output when a static current is detected, effectively signalling a potential failure.

Understanding Earth Leakage Monitoring for 100V Lines Audio Systems

Understanding Earth Leakage Monitoring for 100V Lines

This information is about understanding Earth Leakage Monitoring for 100V Lines.

What is a 100V Line audio system?

A 100V Line audio system, also known as a "constant-voltage system," is a cost-effective and straightforward multi-speaker sound system to set up. These systems are commonly used in large areas where multiple speakers are needed across significant distances, such as in shopping centres, outdoor events, schools, and bars & restaurants.

There are many advantages to using a 100V line PA system, such as running numerous speakers from a single amplifier over large distances without losing audio quality.

What exactly is earth Leakage?

Earth leakage occurs when the current flowing in a system finds an alternative return path other than the active and neutral conductors. In audio systems, earth leakage can lead to mysterious hums and buzzes.

It is crucial to monitor earth leakage in the audio system using the monitoring circuit depicted below.

Digital Input Sensing

Digital input/ Dry Contact input Sensing Circuit



When NC (normally closed) is detected at the input, the microcontroller will receive a Low (0V) signal and a high (5V) signal will be received for NO (normally open).

Short Circuit Monitoring

Comparator Circuit for Open/Short Detection

The Comparator Circuit for Open/Short Detection works as follows:

1. Open Circuit Detection: When there is an open circuit across the input connector, the voltage at V- will be approximately 5.1V, which is higher than the V+ voltage of 2.5V. As a result, the output to the microcontroller will be Low (0V).

2. Short Circuit Detection: In the event of a short circuit across the input connector, the voltage at V- will drop below 2.5V, causing the output to go High (5V).

In addition to open and short circuit detection, this circuit can also be utilized as a simple continuity test by connecting an LED and Buzzer at the output.

Telephone Ring Detector

Analog Telephone Ring Detector

This circuit is designed to detect the ringing signal of an analog telephone. When the circuit detects the telephone ringing signal (60 to 105-volt RMS 20-Hertz sine wave) across the tip and ring, it triggers the Optocoupler's phototransistor output to provide a Low (0V) signal to the microcontroller. If no ringing signal is detected, it will give a High (5V) signal to the microcontroller.

To prevent fault triggering from unwanted signals, a 12V Zener diode is added to the circuit. Additionally, a 0.1uF, 250V capacitor is used for DC blocking, and a 10k 0.5W resistor limits the current passing through the optoisolator.

The output of this circuit can either drive a relay or be directly interfaced with other outputs such as LEDs.

Fuse Monitoring Circuits

Monitoring the fuses from the microcontroller with backup power is a good idea for our design.

AC Fuse Monitoring   



This is a simple AC Fuse monitoring circuit, which will give Low (0V) to the microcontroller when the Fuse is okay and give High (5V) if the fuse is faulty. 4N26, an industry-standard single-channel phototransistor coupler senses the AC voltage and provides good isolation between the main AC input voltage and microcontroller input. The optocoupler consists of a gallium arsenide infrared LED and a silicon NPN phototransistor. The diode 1N4007 with 12V Zener at the optocoupler input prevents false triggering due to abnormal voltage drop on the main input. Another diode with a 120k resistor limits the return current on the neutral line.

DC Fuse Monitoring   

This DC Fuse monitoring circuit is designed to supply the microcontroller with a 5V signal when the monitoring fuse is intact and a 0V signal when the fuse is faulty.

 Under normal conditions, the DC current flows through the fuse, and the forward current of the Optocoupler's LED is below the threshold level, causing the Optocoupler to remain in the OFF state.

 Once the fuse is faulty or blown, the optocoupler is switched ON, pulling down the logic output to the controller.