Feld-Hell electronic circuitry and schematics

Posted on Feb 7, 2014

The 900 Hz tone is generated with an LC-oscillator. The `L` part of the `LC` is provided by the inductance of the oscillator`s output coupling transformer T1. It is a variation on one of the two standard Hartley oscillator configurations (named after its inventor Ralph Hartley, who was awarded the patent in 1920). It has two series-connected (and

Feld-Hell electronic circuitry and schematics

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

coupled) inductors and a single capacitor (here: C18). The two inductors are formed by the tapped windings on one side of coupling/isolation transformer SG ("Summer-G bertrager"). So this transformer cleverly fulfills two functions. When a key is selected via the keyboard, the continuous 900 Hz tone is keyed by the associated track of the character drum ("Geberwalze"). See the " raster can " section of the "how it works" page. The tone can also be keyed with the "Morse" telegraphy key of the keyboard. The keyed tone is output via transformer T2 to the telephone line I/O port ("Leitung" connectors La and Lb/E), and the telephone jack that is connected in parallel to this port. The "Leitung" port has an impedance of 800 ohm (at 900 Hz). This may at first appear to be incompatible with what many people consider to be the (fixed) impedance of standard POTS telephone land-lines: 600 ohm. However, keep in mind that phone lines only have 600 ohm impedance at one single frequency: about 1300-1400 Hz. For 900 Hz (the Hellschreiber tone), the impedance of a standard phone line is actually 800 ohm! At the high end of the phone-voice bandwidth (3400 Hz) the line impedance drops to about 350 ohm. See ref. 1. The impedance of the connected line is not at all critical, as long as the end-to-end attenuation of the 900 Hz tone is less than 46 dB (5. 3 Neper). The "Leitung" port is bi-directional: keyed tones are output to the phone line,...

Visit page

Leave Comment

characters left:

Related Circuits

12V Battery Checker Circuit

This is a 12V battery checker circuit that uses 3 LEDs that light up at their respective voltages. The red LED lights up when the battery voltage is between 8 to 10V, the orange one at voltages...

230V Flasher Circuit diagram

This circuit operates with 230v. you can use this circuit to decorate your parties. I think this will be a wonderful circuit to you all. Here DIAC ER 900 and Triac BTW 11-400.

Automatic light activated switch circuit

The circuit can be used for switching OFF a particular lamp or group of lamps in response to the varying ambient light levels. The unit once built can be used for switching OFF a lamp when dawn...

BC548 Heat Sensor Diagram Circuit

Heat sensor circuit can be used to control any device using heat sensor. In this circuit a thermistor and a resistance is connected in series. This arrangement makes a potential divider circuit....

GSM CELL PHONE JAMMER SCHEMATIC

A wonderful diy gsm jammer or cellular mobile phone jammer schematic diagram for use only in GSM1900 with frequency from 1930 MHz to 1990 MHz. The GSM1900 cellular cell phone network is made use of...

Biosensor circuit

This week was spent completing a number of different objectives. Firstly, the software was downloaded to design the schematic for the circuit to be translated onto a PCB. Much of the week was spent...

Instrumentation circuit

The mechanical chassis prototype, as can be seen from the image on the left, was made using two materials: foam and aluminium. Foam was chosen due to its easy manipulation and aluminium due to its...

Hum Circuit

Although our kit utilizes an off-the-shelf microcontroller (AtMega328P-PU based Arduino), we additionally designed a simplified version. This allows other collaborators and students to potentially...

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

Controlling stepper motors

The first pulse motor that is used to diss it because it is the positioning control things, we...

Laser Power Supply Circuit

This supply generates an initial high voltage for ignition purposes. After ignition, the supply...

DS18B20

Will be examined the digitization of temperature to reveal not enough yet its course of change of...

Power Supply Circuit

The circuit consists of N-MOSFET voltage follower T1 (common Drain) and current source T2 (NPN...

Automatic bathroom light switch circuit CD4022 composed

As shown in FIG bathroom light switch gated automatic way, when someone enters, once the door is...

Bass circuit diagram

Circuit principle: the input signal via IC1-1, and external components of the fourth-order...