Introduction: Fast Edge Square Wave Generator
If you want to measure inductance , capacitance of any component then you need a fast edge square wave in this article we learn about this.
Step 1: Video
For more info you can also check my video.
Step 2: Details
If we want to measure Inductance,Resonance frequency, Capacitance of capacitor,we need fast edge square wave from any good frequency generator but what if we don't have such expensive function generators,we can make different function generator but it don't have fast edges, so we going to make a fast edge square wave.
what is fast edge mean- As we know if we are generating square wave from any device Rising and falling of voltage creates square wave i.e this rising and falling edge should be fast i mean very fast to measure capacitance,inductance as we can see in picture.
Working-
7414N is main part of this project it is a HEX SCHMITT-TRIGGER INVERTER . its first channel are used as oscillator with help of 100nf and 6k capacitor and resistor then rest of 5 channel are used in parallel to decrease output impedance.
you can change c1 and r1 for different frequency levels as you need , i have tested it it works good.
Step 3: Rising Edge Over Shoot (Ringing)
Over Shoot is around 2-3% in my case, Use Filter Capacitor to filter and produce smooth dc at output, don't use Polarity protection diode it makes overshoot more worse. in my case it is fine if you want to damp overshoot more precisely then follow steps below.
Add a hefty capacitor on the breadboard across the supply rails, closest to the IC Start with 100 uF.In parallel with the 0.1 uF decoupling capacitor shown in schematic, and touching the Schmitt Trigger supply pins, add a 10 uF electrolytic capacitor.Trim the leads of all 3 capacitors above to the bare minimum which will still make positive contact with the breadboard contacts. Those leads are adding inductance you don't want.Add a load from the output you are reading to the ground pin, as close to the output pin as possible - 220 Ohms should be fine, and again you want leads trimmed to minimum.If you absolutely must avoid overshoot / undershoot beyond a few hundred milliVolts, add small signal Schottky diodes from the output pin to both supply and ground pins as shown in Picture.
This will ensure that the peak on the rising edge and trough on the falling edge of the ringing are damped - there will be some effect on the respective trough / peak of the ringing as well because of the excess energy of the peaks being dissipated across the diodes.Finally, the breadboard, due to the nature of its construction, introduces capacitance, inductance, and all kinds of parasitic coupling. Even a simple perf-board will do better. Long leads simple exacerbate this problem, especially at high frequencies / sharp transitions, where even a simple wire lead is a source of coupling and inductive ringing.
