PCB Design Guidelines

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Simple Security Wire Loop Alarm Circuit

A wire loop is used to protect valuable objects in this simple alarm circuit. The electronic hobby circuit is powered by a 9v battery. The alarm beeper is activated if the wire loop is severed. The standby current is so low that the 9v battery should last for many years.

Light to Frequency Converter

This circuit uses a CMOS version of the classic 555 timer, to form a light intensity to frequency converter. A small PIN photo diode is used as the light detector. The pulses produced are short, so in some applications you may want to stretch them or feed them through a flip/flop to produce a square wave signal. Although the circuit shown is designed for a 5v supply, it could operate from almost any voltage from 3v to 15v.

The 555 timer circuit is configured as a free running oscillator. When a PIN photodiode is reversed biased, it leaks current proportional to the light intensity hitting lt. The photodiode leakage current charges the 0.01uF capacitor. When the voltage of the capacitor reaches about 2/3 of the supply voltage, the pin 3 output of the 555 timer swings low. This state quickly discharges the capacitor through the photo diode, until the capacitor voltage is less than 1/3 of the supply voltage. This causes the pin 3 output of the 555 to swing high again, for another charge cycle. With the component value chosen, the frequency of the oscillator will range from about 1Hz in total darkness to about 25KHz in sunlight. Other frequencies are possible by changing the value of the 0.01uF capacitor.

Click on Schematic below to view PDF version of this Circuit

3v Low Battery Voltage Flasher Circuit

Many battery powered devices use two AA alkaline cells. Often you will not know when it is time to replace the batteries until the device powered by them actually stops operating. The hobby circuit below can be connected to a 3v battery, to give you some warning when the battery is nearing its end of life. It will flash a LED when the battery voltage drops to about 2.4 volts. The electronic circuit draws only 1ua of current in standby mode and jumps to only 20ua when flashing, so it can safely be included without depleting the battery energy. A voltage detector IC from Panasonic (Microchip also makes similar devices) is used to monitor the battery voltage. The device’s open drain output swings low, when the battery voltage is below 2.4 to 2.5 volts. This action turns on the two transistor oscillator circuit, which drives the LED with short current pulses lasting only 2ms. I published this Flasher circuit in the January 2 issue of EDN magazine in 1997.

Remote LED Indicator Light

There are times when you would like to transmit a signal from one LED indicator light to second LED at another location. The circuit below works well for this application. It takes advantage of the fact that the internal infrared LED inside an opto-isolator has a lower voltage drop than the visible LED being tapped into. Using a darlington type opto-isolator also means very little current needs to be diverted to the isolator. The photodarlington side of the isolator can be used to turn on the remote LED using any convenient DC source. In automotive applications, this is often 12v. You can also use the output of the opto-isolator to drive a low power beeper. This might be handy for something like a “check engine” or a “windshield washer fluid” light.

Click on Schematic to view PDF

PCB Design with TINA

Create single, double-sided or multilayer PCBs of your circuits with a single mouse click, using automatically-placed and routed components. All components in TINA are "PCB-ready" and have associated footprints. If necessary, you can review and edit a component's footprint using the components' spreadsheet. TINA's unique 3D capability displays a schematic with the physical parts in place of their electronic symbols. You can also view the PCB in 3D from any angle to see how it will look after manufacture.

The fully integrated layout module of TINA 7 has all the features you need for advanced PCB design, including powerful autoplacement & autorouting, flexible PCBs, manual and "follow-me" trace placement, DRC, forward/back annotation, pin/gate swapping, keep-in/out areas, thermal relief, fanout, plane layers, Gerber file output and much more.

Single layer SMD circuit

Schemaric diagram

Schematic with 3D view of parts

Single sided layout

3D view of the circuit

Double layer through-hole circuit

Schematic diagram of a double-sided design

3D part preview on the schematic

PCB layout with Top (red) layer selected

PCB layout with Bottom (green) layer selected

3D view of the top side

Looking at the bottom layer

4-layer SMD circuit

Schematic diagram of the 4-layer SMD design

PCB layout of the 4-layer SMD design

3D view of the top side

3D view of the bottom side

Flexible PCB Layout (Flex PCB)

Flex PCBs are PCBs whose electronic devices are mounted on flexible plastic substrates. They are widely used in modern electronics where space is a critical factor e.g., cameras, mobile phones, etc. TINA supports Flex PCB design, which we will introduce by way of an example. Our example will consist of a conventional rigid PCB with two flexible extensions.

Example file „PIC Flasher DIP4SW flex top.TSC” from the Examples\PCB folder of TINA.

TINA can present a 3D view of the circuit board. Press the rightmost button (3D View) in the TINA PCB Designer program see the PCB as presented in the next figure.