You Have Mail!

Posted on Feb 5, 2014

If your letterbox is some distance from your house, you will find a monitoring device useful to indicate when new post has arrived. This can take the form of a US-style visible flag; a more modern alternative uses a 433 MHz radio transceiver. The big advantage of the solution presented here is that is can use an existing two-core bell cable, witho

Click here to download the full size of the above Circuit.

ut requiring any further power source. The arrival of post is signalled by a blinking LED; for added effect, a digital voice recorder can also be connected which will, at regular intervals, announce the fact that the letterbox needs emptying. The device is silenced by a reset button. The circuit uses one half-cycle of the AC supply to power the bell or buzzer, and the other half-cycle for the post indicator. Suitably-oriented diodes in the device and in the letterbox ensure that the two signals are independent of one another (Figure 1). The bell current flows from K1. A through D3, bell-push S2, D1 and the relay back to K1. B. C1 provides adequate smoothing of the current pulses to ensure that the relay armature does not vibrate. The bell is operated by the normally-open relay contact. If the bell is actually a low-current piezo buzzer, then it can be connected directly and the relay dispensed with. During the half-cycle for the letterbox monitor current flows from connection K1. B on the bell transformer through current-limiting resistor R1, the LED in the optocoupler, reed contact S1 (a microswitch can also be used) and D2 and finally back to K1. If the reed contacts are closed, the LED in the optocoupler will light and switch on the phototransistor. A positive voltage will then appear across R3 which will turn the thyristor on via C6. The red LED will indicate that post has arrived. Pressing S3 shorts out the thyristor,...

Visit page

Leave Comment

characters left:

Related Circuits

Tesla Coils Wiring

Because of the high voltages found in a Charge & Primary sections it seems natural to look for cable with high voltage ratings, such as neon sign cable, medical X-ray equipment cable & car engine...

simple bus level-shift / I2C mosfet level converter Fairchild BSS138

While doing some background reading about the Philips I2C bus I came across an application note written by Herman Schutte (of Philips Semiconductors Systems Laboratory in Eindhoven). Mr. Schutte...

making a coolpix e990 dual USB / serial cable

How to make a combined / dual serial and USB cable for the Nikon Coolpix 990 (e990) camera.

PC/CP120 Digital Logic Design

A Dual Inline Package, or DIP switch can be used to select between 0 and 5 volts at some point in a circuit. Since the dip switch does not have any power or ground connectors this must be done...

Vehicle Sensor Control for Parking Lot Management System

As the title indicates the goal of the project was to develop a parking lot management system. In this project we had reduced our project into 5 design phases. In order to acheive the goal, we...

thermostat design

We are planning to use a Programmable Logic Device to control our seven-segment displays. This will be accomplished by using the 8 outputs from the Analog to Digital converter as the inputs to the...

The Cylonduino Arduino Experiement

I`ve been putting in a lot of extra hours at work the last week in anticipation of an editing deadline. Despite this, I thought it was about time that I attempt a little hardware hacking. Even...

measuring battery capacity with an arduino

I needed a couple of AA batteries and found the display at the supermarket where they were all arrayed. Normally when I`m shopping in the supermarket, I tend to look at the price/kg or price/l when...

New Circuits

Zero consumption Anti-theft High power Code Switch for E-Bike Batteries

This project fits more for custom made battery casing that can have more space to hide things inside. This switch with few alterations can be used for any other project as well but is designed based on e-bike needs! This project use a clever functionality of....
Ultrasonic distance finder circuit

The circuit described here uses ultrasonic oscillations and operates based on the propagation velocity of these oscillations in the air. Thus, we can easily determine the distance of two points if the time within which the wave travels this distance is....
Simple Metal detector circuit with CD4030

Sometimes the precious metals are hidden too deep and are not detected except with complicated devices. In many cases, however, small pieces of precious metal buried near the surface can be detected by relatively simple means. Everyone is very attractive to....
Fully automatic watering circuit for flower pots

Many times for various reasons we forget or can not water the plants that we have in our homes. And many humidity sensors units just notify us with a beeping sound or with a flashing light, that the pot needs watering. But what if we are away from home? This....
Simple deep searching metal detector circuit

The principle behind a metal detector is really very simple. Proof of this is the circuit that follows, in which it proves that the construction of a metal detector can be done in the minute, with few components that we find very easily everywhere. With the....
Sub-Harmonic Bass Converter for Electric Guitars

The sub-harmonic bass generator is a sound producing unit for guitars. The sound it produces looks very much like that of the bass guitar. The octave generator is sometimes quite unusual since it does not produce any of the usual ways of coloring the sound,....
Echo Depth Sounding Sonar for Boats

In the past the sounding (sea bottom measurement) was done with the "bullet", that is, with a heavy lead object that the seamen plucked into the sea hung from a calibrated rope. As soon as the "bullet" reached the bottom, the depth appeared directly from the....
100W HiFi Audio Amplifier Circuit

This Amplifier was designed to have the following specifications: Distortion less than 0.1% at full power of 100W even at 20KHz. Power has to be attributed to an extended bandwidth. The output transistors must be protected against short circuits. The power....
Plant-Pot Water Level Indicator Circuit

A series of LEDs serve to alert the gardener when plants need water. Using two conventional digital integrated LEDs and a series of LEDs, we make a very useful device for gardening. The device detects the amount of water in the pot and alerts the grower.....

Create NOW your QR MENU for your Restaurant / Hotel / Bar / Caffe,

Comprehensive ordering/paying features. fully personalized to suit your Business.

Update Anytime! Easy and Simple!

Popular Circuits

Magnetic Gun

Picured in Figure 1 is a miniature magnetic gun. When optimally tuned, it will propel a small...

touch alarm system

Touch Alarm circuit is widely used for security, which is installed on the door. The advantages...

Simple Audio amplifier Using Transistors

Build a simple audio amplifier using transistors. I know there are IC designs specifically for...

wave antenna circuit

The circuit presented here illustrates the fact that in spite of all kinds of new component and...

Simple Telephone Timer Circuit PCB

Telephones are reaching its death point all over the world. however there is more than 350...

Simple Stereo VU Meter

This project will indicate the volume level of the audio going to your speakers by lighting up...

Simple Microphone Preamplifier Project

This is a simple microphone preamplifier circuit which you can use between your microphone and...

Audio Equalizer Circuits

This discussion continues on from the audio tone control topic, which introduced both passive and...

Simple lock circuit can alarm

Circuit works: Figure 5 -2a in S. Alarm switch. If you press S, after the relay K. Electrical...