electronic electroscope

Topics: Electric charge, Electricity, Electron Pages: 6 (1081 words) Published: October 24, 2013
 ELECTRONIC ELECTROSCOPE

Abstract— An electroscope is the instrument used to detect charged bodies. Here, an electronic version of the scope that is more sensitive as compared to its conventional counterpart and which helps indicate the polarity of charge has been described. This circuit consumes very low quiescent power and reliably indicates charge induction and detection. The polarity of charge is indicated through LEDs (green LED indicates positive and red LED negative).  In this project report, the detailed circuit diagram of the electronic electroscope has been given in which dual timer IC556 and two input NAND gate IC CD4011 have been used followed by its working in which few observations with regards to the glowing of the LEDs have been made. This is followed by the explicit mention of the applications of electronic electroscope. A list of important components that form an integral part of this project topic has been made.

1.Introduction

In most experiments dealing with static electricity, an electroscope is required to indicate the presence of small amounts of positive or negative charge in laboratories, gold leaf electroscopes being one of them. However, these gold leaf electroscopes may be too delicate and costly for the average home experiments. An alternative to this is the electronic electroscope which is not only rugged and inexpensive,but is as sensitive as the gold leaf electroscope. An electronic version of the scope is more sensitive as compared to its conventional counterpart and helps indicate the polarity of charge in any charged body.

In Section 2, the circuit diagram as well as the pcb layout of the electronic electroscope has been given. In Section 3, the working of the circuit has been explained in detail along with some important observation. Section 4 contains the list of components that are essential for building the circuit. Section 5 enlists few applications of the electronic electroscope. In Section 6, relevant conclusions have been drawn.

2. Circuit Diagram:

Pcb Layout:

3.Working:
The diodes D3 and D4 (1N4148) help determine the direction of current flow, removing certain shortcomings of the circuit. (These prevent the capacitor of the opposite arm from charging when the object is withdrawn quickly.) Even though diodeD4 in series with capacitor C6 is reverse biased, the current through it is adequate to charge capacitor C6. Thus capacitor C6 gets charged with respect to the ground and the input voltage of gate N1 goes high. This makes the gate output low and transistor T3 conducts to light up the green LED.

The process is similar during negative charge detection. Here transistor T4 conducts to light up the red LED. When a negatively charged object is brought near the detecting wire, it also affects the positive-detecting wire. The negatively charged object pushes the electrons in the positive-detecting wire towards its input capacitor and the wire becomes negatively charged with respect to the ground. These electrons leak through the gate input into the other parts of the circuit.  

When the negatively charged object is withdrawn, the positive-detecting side having lost electrons (detecting wires and the capacitor) appears to be positively charged. Since this voltage may not exceed the supply voltage (V+0.6), the gate will not conduct heavily to return the electrons immediately. In this case, the charge developed across the capacitor takes a long time to decay and the gate becomes locked. 

To overcome this problem, two monostable multivibrators built around IC1(A) and IC1(B) have been incorporated for each arm. The high output of monostable IC1(B) shorts capacitor C6 to the ground for a specific time as soon as the output of the...
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