PWM Generator Circuit

PWM Generator with Current Limit Circuit


PWM using 555

IC1 astable gives a fixed square wave at pin 3, C1 and R1 derive
uS trigger pulses from IC1 and this will trigger IC2 monostable or
single shot, the voltage at pin 5 of IC2 will change the pulse width
output of IC2, to get it working all the three RC combinations
have to be figured out


A Simple PWM Circuit Based on the 555 Timer

The 555 timer in the PWM circuit is configured as an astable
oscillator. This means that once power is applied, the 555 will
oscillate without any external trigger. Before the technical
explanation of the circuit, let's look at the 555 timer IC itself.


PWM generator

Here is an assembly very simple to get an oscillator giving
a fixed frequency signal but variable duty cycle. It can - after
amplifier transistor - serve to control the rotation speed of a motor
with direct current or to adjust the power of a dew-heater. We use
once again a logic gate of a CD4093 circuit.


Opamp PWM Generator Circuit

This uses the LM324, a 14-pin DIL IC containing four individual
op-amps and running off a single-rail power supply.
The sawtooth is generated with two of them (U1A and U1B),
configured as a Schmitt Trigger and Miller Integrator, and
a third (U1C) is used as a comparator to compare the sawtooth
with the reference voltage and switch the power transistor.


PWM Generator Circuit by Digital register method

an example circuit using the digital comparison method
when a microcontroller is available to set the 4-bit digital register
value. A write strobe is required from the micro to latch the 4 data
bits into the register. The 74HC161 counter is free-running,
the frequency being set by the 74HC14 oscillator section, where
it is roughly f = 1/(6.3RC). The resulting frequency of the PWM
signal will be 16 times less than this counter clock frequency,
since it requires 16 pulses to complete one "revolution" of the
counter. With R=2k and C=1nF this results in a counter
frequency of approximately 80kHz which will result in a PWM signal
frequency of 5kHz.


0 - 100% PWM generator Circuit

The next circuit I found is actually a concoction of 2 separate
designs that cunningly come together to form a 0 - 100% PWM
generator. The first stage uses a single 555 timer to generate a
constant saw tooth waveform.

Yes I know that we don’t want a saw tooth but it can be easily
converted to PWM. If you look at the saw tooth you can see
that it is a wonky triangle, but wonkyness aside it has a fat bottom
and a thin top (just like most triangles).

Intercom circuit

2-Line Intercom-Cum-Telephone Line Changeover
Circuit
The circuit presented here can be used for connecting two
telephones in parallel and also as a 2-line intercom.
Usually a single telephone is connected to a telephone line.
If another telephone is required at some distance, a parallel
line is taken for connecting the other telephone. In this
simple parallel line operation, the main problem is loss of
privacy besides interference from the other phone. This
problem is obviated in the circuit presented here.

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Doorphone Intercom
A simple 2 way Intercom based on the LM386386 using 8 ohm
speakers.

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High Quality Intercom
This circuit consists of two identical intercom units. Each
unit contains a power supply, microphone preamplifier, audio
amplifier and a Push To Talk (PTT) relay circuit. Only 2 wires
are required to connect the units together. Due to the low
output impedance of the mic preamp, screened cable is not
necessary and ordinary 2 core speaker cable, or bell wire may
be used.

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Low-cost Transistorised Intercom
The circuit comprises a 3-stage resistor-capacitor coupled
amplifier. When ring button S2 is pressed, the amplifier circuit
formed around transistors T1 and T2 gets converted into
an asymmetrical astable multivib-rator generating ring
signals. These ring signals are amplified by transistor T3 to
drive the speaker of earpiece.

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Multi-station intercom uses CB microphones
This intercom unit can connect any number of units together,
rather than the limit of two, as with most designs. In practice,
the number of stations required would normally number less
then 10.

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Simple Intercom
Very simple and useful circuit for communication between two
person. The Q1 is used to amplify the weak output signal
of speaker when one push his (her) side push-button to speak.

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TWO-WIRE INTERCOM

This is a very interesting circuit using 2 transistors in each
station to drive a high impedance speaker. 8R speakers will
work quite well and this is an ideal project to connect between
your work-room and the kitchen so you can be told when dinner
is ready!

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STAGE INTERCOM SYSTEM
The intercoms were designed so that they can be added at will to
any part of the link line. The Link is a 2 core 14 strand speaker
cable of pretty standard quality but it provides almost a noise free
connection.

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The Ferris Intercom
The movie "Ferris Bueller's Day Off" is a high school comedy
from 1986. It was a rather popular movie at the time and
for years afterward. Anyway, in the movie, there was a scene
where Ferris's high school principle (Mr. Rooney) comes to
Ferris's home and pushes the intercom button. Ferris should
be at home sick, but of course he is out for a day, living it up.

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