The circuitry for the tone detector, solenoid driver, and motor speed control (paper transport and spindle) is rather straightforward. A solid-state implementation of the driver circuit typically needs a diode (installed with reversed polarity) across the magnet solenoid, to avoid damage due to the inductive voltage spike upon de-energizing the solenoid.
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This is referred to as a flyback, snubber, freewheeling, catch, or suppressor diode. If the relay is a bit slow when energized, you may try to speed it up with one of the simple circuits described here. They basically briefly apply almost twice the supply voltage to the relay coil when energizing. The capacitor in the circuit will have to be adapted to the desired speed and relay (decay time). Paper transport speed calibration is easy: all you need is a stopwatch and a ruler or tape measure. Simply adjust the motor rpm to obtain about 47 cm per minute. Unlike the spindle in a Feld-Hell machine, my spindle is a single-thread (1-start) worm. It needs to turn at 7 columns per character x 2 ½ characters per sec x 60 sec/min = 1050 rpm. The Feld-Hell machine has a double-thread (2-start) spindle: it has two intertwined windings. Note that the number of threads is not related to the number of turns of each thread! Both the Feld-Hell and my homebuilt spindle have two turns. The Feld-Hell spindle only needs to turn at ½ x 1050 = 525 rpm, to get the same effect as a single-thread spindle at 1050 rpm. Adjusting the spindle speed to 1050 rpm can be done several ways: 1) first get the electro-magnet to work properly (which you have to do anyway, hi), then feed the printer with "known-good" Hell-audio and adjust the rpm until the print becomes legible and the text lines are horizontal; or 2) use a tachometer. I used method nr. 2 by...
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....
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....
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....
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....
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....
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,....
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....
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....
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.....
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