Dummy Alarm Project

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This Dummy Alarm project makes an LED flash briefly once every 5 seconds to imitate the indicator light of a real alarm. The circuit is designed to use very little current to prolong battery life so that it can be left on permanently. An on/off switch is not included, but could be added if you wish.
The 7555 timer IC used is a low power version of the standard 555 timer. A 'superbright' red LED is used because this provides a bright flash with a low current. The LED is off for most of the time so the average total current for the circuit is less than 0.2mA. With this very low current a set of 3 alkaline AA cells should last for several months, maybe as long as a year.
The circuit will work with a standard 555 timer IC (such as the popular NE555) but this will increase the average current to about 2mA and the battery life will be much shorter. You can use a greater supply voltage (15V maximum) for this circuit but the 1k resistor for the LED should be increased to keep the LED current low at about 3mA. For example to use a 9V PP3 battery change the 1k resistor to 3k3. Note that AA cells will last longer than a 9V PP3 battery.
This project uses a 555 astable circuit.

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Parts Required

• resistors: 1k, 10k, 680k
• capacitor: 10µF radial
• LED: red superbright, 5mm diameter
• 7555 low power timer IC
• 8-pin DIL socket for IC
• battery clip
• 4.5V battery box for 3 AA cells
• stripboard: 8 rows × 16 holes

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Stripboard Layout

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Circuit diagram

Flashing LED Project

LED stands for Light Emitting Diode
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This project is designed as an introduction to soldering, identifying common components, using the resistor colour code and placing components correctly on stripboard. The LED flashes at about 3Hz (3 flashes per second). This project uses a 555 astable circuit.

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Parts Required

• resistors: 470, 1k, 220k
• capacitor: 1µF 16V radial
• red LED (or orange, yellow or green if you prefer!)
• 555 timer IC
• 8-pin IC holder (a 'DIL socket') for the 555 IC
• battery clip for 9V PP3
• stripboard: 6 rows × 21 holes

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Instructions

1. Solder the 8-pin IC holder in the correct place on the stripboard.
2. Break the 4 tracks under the IC holder with a track cutter tool. You can allow extra holes if your piece of stripboard is large enough.

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3. Use the resistor colour code to identify the resistors which are marked with coloured bands to show their value.
4. Insert and solder the resistors in the correct position, they can be put in either way round, but you must line them up correctly with the IC holder.
5. Identify the other parts, then solder them in the correct position and the right way round. To help you identify the parts please see our page on soldering.

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6. Solder the 2 wire links in place around the IC holder, it is easier to use plastic-coated single-core wire. (The flexibility of stranded wire is not needed for connections like this and the strands can be difficult to push through the small hole).
7. Finally insert the 555 timer IC and connect a battery!

Water level buzzer

Specifications

Water Level Buzzer is a simple kit which will buzz when water reaches the sensor level. Input - 9 VDC @ 40 mA Output ??? Buzzer Terminal pins for Supply voltage Power-On LED indicator Four mounting holes of 3.2 mm each PCB dimensions 32 mm x 35 mm

Schematic

Parts List

PCB

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2500W Phase Control
author: Hans-Juergen Zons [hjzelec @ freenet.de]

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This circuit controls resistive and inductive loads up to 2,500W. Its main functional device is an integrated phase control circuit - Siemens TLE3103. It contains its own power supply, a zero voltage crossing detector circuit and a logic driver. An additional feature is the low voltage input to enable/disable triac firing enabling/disabling the logic driver. The function is as follows: pin13 TLE3103 open (floating), trigger output active, tied to ground trigger output disabled.

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Description

An UP and a DOWN pushbutton control a 32-step digital potentiometer (IC2, AD5228) via the debouncer IC1 (MAX6817). The digital potentiometer has a power on reset pin which might be tied to ground causing the potentiometer to start at midscale, or to VCC causing it to start at zero scale. The desired function is selectable using jumper JP1. The triac (capable of driving 40A loads) is a bit overkill for the desired power but the BTA41 has an isolated body and therefore handling of the board under voltage is less dangerous as it is with phase on the package. The snubber circuit uses a 68μH inductance but this might be replaced with a 100 resistor. When replacing the inductance C5 should have a value of 47nF.

Board: Purely single sided, measurements: 3.54X2.15 inches (87.63X54.61mm)

Remark: The debouncer circuit is manufactured with a SOT23-6 package. It might be soldered directly onto the board (DIP-6 package) using thin wires or an adapter board.

Circuit designed by: Hans-Juergen Zons 102 Moo 9 Lampasak T. Dong Mon Lek Mueang, Phetchabun Phetchabun 67000 Thailand Email: hjzelec@freenet.de

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Parts List

Part Value Package
C1 100n C-5
C2 100n C-5
C3 100/16 ELC3,81
C4 22n C-5
C5 10n/250VAC C-15
D1 1N4005 DO41-10
IC1 MAX6817 AD-SOT23
IC2 AD5228 DIL08
IC3 TLE3103 DIL-14
J1 TE-03 TERMINAL 5.08
J2 TE-03 TERMINAL 5.08
J3 TE-03 TERMINAL 5.08
L1 68H/3A DS30A
Q1 BTA41-600 TOP3
R1 120R R-10
R2 18K/2W R-18
R3 820K R-10
R4 180K R-10
R5 56K R-10
S1 UP BUTTON-02
S2 DOWN BUTTON-02

PCB

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Sound Level Indicator

INTRODCTION:


This project uses an LM3915 bar-graph IC driving two sets of ten LEDs for a 30dB range. The circuit is unique because it has an additional range of 20dB provided by an automatic gain control to allow it to be very sensitive to low sound levels but it increases its range 20dB for loud sounds.

The LEDs are operating at 26mA each with the brightness control at maximum, which is very bright. The circuit has a

DIGITAL GEAR INDICATOR

 Introduction


This is a new design for a universal gear indicator that can be fitted to any motorcycle as an aftermarket accessory. Its main advantage is that its operation depends entirely on the gear shift lever movement, instead of connecting to speedometer and tachometer sensors (found in expensive commercial devices), which are rarely available in older motorcycles. It consists of a main circuit including a 7‑segment LED indicator, two Hall sensors that are attached to the motorcycle frame, and a small magnet placed on the gear shift lever.

10W Mini Audio Amplifier

Generally, an amplifier or simply amp, is a device for increasing the power of a signal.
In popular use, the term usually describes an electronic amplifier, in which the input "signal" is usually a voltage or a current. In audio applications, amplifiers drive the loudspeakers used in PA systems to make the human voice louder or play recorded

Free Electronic Project Schematics - Audio Signal Tracer

Free Electronic Project Schematics - Audio Signal Tracer Circuit

This schematics function is to enable one to trace an audio signal through a maze of wires running around the house.

 

Message Recorder Digital Electronics Project

Introduction

The purpose of this digital electronics project is to record messages using a dedicated voice recorder integrated circuit. Recordings are stored in a non volatile memory cells, which means that the message will still be saved even though power has been removed from the device.
Winbond’s ISD2500 Series provide high-quality, single-chip, Record/Playbacksolutions for 60 seconds to 120 seconds message applications. The CMOS devices include an on-chip oscillator, microphone preamplifier, automatic gain control, antialiasing filter, smoothing filter, speaker amplifier, and high density multi-level storage array. In addition, the ISD2500 is microcontroller compatible, allowing complex messaging and addressing to be achieved. Recordings are stored into on-chip nonvolatile memory cells.

Circuit Description

The ISD25120 has several modes of operation. The mode used here is as a multi-message recorder. You may record as many messages as you want up to 120 seconds of memory space.
Put the SPDT switch into the Record position and just push & release the Start/Pause button to start recording. The Record LED goes on. Push the Start/Pause button to Pause - stop recordingThat is the end of Message 1. Sometime later you can record a follow on message, Message 2, by pushing the Start/Pause button again. When you put the switch to Play the messageswill playback. Only one message will be played back at a time. You must push Start/Pause again to get the next message. The Reset switch will move the internal address pointer back to the start of the memory space.