Most people who want to modify and improve their Spectrum look first at the keyboard as a prime area for change. But straightforward replacement involves digging around inside the computer - something of a put-off, for two important reasons. To begin with it might nullify the guarantee from Sinclair and, frankly, there`s just no-one else around to undertake this kind of
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repair work (there`s no published circuit diagram and a lack of certain specialised parts). Secondly, it`s easy for damage to occur when fitting the keyboard to the computer or mounting the keyboard in a separate case (which requires the removal of the complete circuit board from the casing of the computer). So what`s outlined here is a keyboard buffer that fits on the back of the ZX Spectrum, connecting to the real expansion port. It can easily be fitted or unplugged for testing, and should your Spectrum develop a fault, it can be removed without trace for guarantee purposes. The Sinclair keyboard, like many others, works on a matrix of keys where each key connects up two wires. The combination of the incoming and outgoing wires is continually being tested by the computer to see which one has been pressed. On the ZX Spectrum the keyboard has eight incoming wires - the upper eight address lines. These are tested by holding only one of them to a Binary 0 (a LOW signal) and seeing what the result is on the incoming (data) lines. If a switch has been pressed on the address line being tested, then the LOW signal will be passed on to the data line to which it is connected. Until then the data line will be held to a Binary 1 by the resistors connected to the five data lines. In the keyboard layout diagram (Figure 1) the keys as you can see are arranged in a similar order to the keyboard (but not in the familiar QWERTY layout)....
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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