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Electronic electroscope Essay

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(These prevent the capacitor of the opposite arm from charging when the object is withdrawn quickly.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 negative-sensing gate (N4) goes from high to low. Similarly, the high output of IC1(A) charges capacitor C1 for a specific time as soon as the output of the positive-sensing gate (N1) goes from low to high.

A similar arrangement is provided for both the positive- and negative-detecting sides. So when a positively charged object is withdrawn, the negative-charge-detecting input capacitor is shorted. The monostables prevent locking of any of the two gates and allow the scope to function smoothly. Some of the observations made are as follows: The circuit achieves quiescent state i. e. , both LEDs go off in the absence of a newly charged object. The normal positive charge on a person was detected. Two bodies rubbed against each other had consistent opposite charges.

The LEDs glow for a sufficiently long time and then go off (i. e. , a balance is set up with the external potential difference). When a positively charged body is brought near the detector wires, the green LED glows. When a negatively charged body is used, the red LED glows. It is possible to use the scope as a direct charge detector within limits by bringing the corresponding plates (or just the lead) in direct contact with the point of charge accumulation in a circuit. The sensitivity can be increased to some extent by decreasing the values of capacitors C1 and C6.

Electric charge can build up on a spacecraft when it is orbiting Earth or traveling in space. Excess charge build up is dangerous to a spacecraft’s delicate electronics, and can be harmful to astronauts on space walks. The electronic electroscope can be used to detect this excess electric charge on the spacecraft. 6. Conclusion: The crux of the electronic electroscope lies in the glowing of the LEDs which is an indication of the presence of static electricity in the everyday objects that are found in nature. The inclusion of dual timer IC 556 and two input NAND gate IC CD 4011 has helped obtain the desired output.

The negative and positive detection plates incorporated in this project can be replaced by any conducting body e. g. copper wire devoid of insulation. Human body is observed to be positively charged, so when the positive detection plate is brought in human contact, the green LED glows. 7. References: [1] Electronic Electroscope, [Online] Available: http://electronicsforu. com/newelectronics/lab/ [2] Detect charged bodies with electronic electroscope,[Online]Available: http://www. edn. com/design/analog/4417628/Detect-charged-bodies-with-electronic-electroscope

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