Enostaven merilnik varnostnih nalepk

MLAKAR PACHECO, MATEJA (author), Vidmar, Matjaž (mentor), Blatnik, Aljaž (co-mentor)

V diplomskem delu sem opisala načrtovanje in izdelavo radiofrekvenčnega instrumenta – grid-dip metra (v nadaljevanju GDM). Cilj naloge je bil izdelava GDM-ja, z možnostjo nastavitve na avtomatični ali ročni prelet. V avtomatičnem načinu je na XY osciloskopu prikazan izmerjeni dip. Delovanje instrumenta je bilo preverjeno na primeru varnostnih nalepk proti kraji blaga. Grid-dip meter je eden od osnovnih radiofrekvenčnih instrumentov. Zaradi njegove preprostosti je njegova točnost vprašljiva, zato ga dandanes ne zasledimo tako pogosto. GDM lahko izmeri resonančno frekvenco in preveri aktivnost radiofrekvenčne nalepke. Izdelani grid-dip meter temelji na radiofrekvenčnem oscilatorju negativne upornosti. Negativna upornost je dosežena z vezjem dveh N-kanalnih in dveh P-kanalnih tranzistorjev z induciranim kanalom iz CMOS integriranih vezij družine 40xx z aluminijevimi vrati. Vezje grid-dip metra je načrtovano v programu SprintLayout in narejeno na enostransko tiskano vezje. Najugodnejša karakteristika je bila ugotovljena s poizkušanjem različnih kombinacij uporov in čipov. Varnostne nalepke delujejo okoli 8 MHz. Število ovojev tuljave je bilo nastavljeno tako, da pokriva območje osciliranja med 5 MHz in 12 MHz. Delovanje GDM-ja je bilo preverjeno z osciloskopom in aktivirano varnostno nalepko.

• Language: Slovenian
• Keywords: Grid-dip meter, GDM, varnostne nalepke, oscilator
• Work type: Bachelor thesis/paper
• Organization: FE - Faculty of Electrical Engineering
• Year: 2022
• PID: 20.500.12556/RUL-140397
• COBISS.SI-ID: 122075139
• Publication date in RUL: 14.09.2022

Secondary language

• Language: English
• Title: Simple security-tag reader

Abstract

In my diploma thesis I described the design and construction of a radio-frequency instrument - a grid-dip meter. The design goal was a solid-state grid-dip meter allowing both automatic and manual frequency sweep. In the automatic mode, an XY oscilloscope is used to display the measured dip. The operation of the assembled instrument was tested on practical security tags. The grid-dip meter is one of the fundamental radio-frequency instruments. Due to its simplicity, it lacks accuracy and today it is less popular than many years ago. A grid-dip meter can measure the resonance frequency of a security tag and its activity. The proposed grid-dip meter is based on a negative-resistance radio frequency oscillator. The negative resistance is generated by two N-channel and two P-channel enhancement-mode MOS transistors contained in standard aluminium-gate CMOS logic of the 40xx series. The circuit of the grid-dip meter is built on a single-sided printed circuit board. The latter was designed in the SprintLayout software. The printed-circuit board was etched and the discrete components were soldered on. Different CMOS chips were tried as well as different bias resistors for best performance. Security tags operate around 8 MHz. The number of turns of the oscillator coil was adjusted to cover the frequency range from 5 MHz to 12 MHz. The operation of the finished grid-dip meter was checked with an XY oscilloscope and an active security tag.

• Keywords: Grid-dip meter, GDM, security-tags, oscillator