Voltage VU Meter - small stupid project, need help - Page 1
Forum section: electronics / projects

author: zmantana
author_rank: Newbie
timestamp: December 19, 2020, 04:28:07 pm
content: Hello everyone, I need help from someone on a small little project I am developing for myself. I am not advanced in electronics... Amateur is an overated statement... anyway, I want to build a small 11 LED VU Meter to keep track of a DC voltage input that varies from 6.2V to 12.4V. I built 3 prototypes based on trial and error, I even tried using a LM3815N (but I think I damaged it) and no luck... I built this rather basic schematic in multisim of what I imagined would be the thing that I want. V1 is the supply that varies in Voltage, the LEDs are actually white not blue and the transistors that I have (recycled) are BC536. Could someone help me make this project? If is to big of a hassle don't bother wasting your time, it's not urgent and not extremely necessary, it's just something I want to build in order to better understand how BJT-s are working and what is wrong in my train of thought. Thank you in advance! (Sorry if my English is bad)

author: bob91343
author_rank: Super Contributor
timestamp: December 19, 2020, 06:25:24 pm
content: My first glance shows that you are drawing too little current. I don't know the beta of those transistors, and you are relying on forward drop of a diode and a transistor junction as voltage standards. Perhaps if you reduce the resistor values it might work. But as the voltage rises, the first transistor draws more and more current, robbing the rest.The principle looks doable.

author: CaptDon
author_rank: Super Contributor
timestamp: December 19, 2020, 08:13:43 pm
content: VU Meter is Volume Units and normally referencedby increments of Decibels. The I.C. series you usedcontains both a linear 0-100% in 10% incrementsas well as a 10 segment 30Db 3db per segmentI.C. Volume units are measured with a ballistic factorto simulate the inertia of an analog panel meter.Mike Durrough used a pair of DB segmented driversin parallel driving the same set of LEDs. He used DOTmode and set it up for peak response with fast decayand then he also had a BAR GRAPH mode set to respondand decay in Volume Units!!! We used them in all ofthe broadcast studios I worked in. I thought thoseDurrough 'Loudness Meters' were one of the coolestideas to hit studio audio in 50 years!! Those driverI.C.'s can be daisy chained also, even mix linear andlogarithmic in the same chain if you're mentally unstable!!

author: hugo
author_rank: Regular Contributor
timestamp: December 20, 2020, 03:23:18 am
content: The circuit works to some degree as a crude voltage indicator, it's not accurate and needs some adjustment (all 11 LEDs should turn on for 12.4v input) ...

author: CaptDon
author_rank: Super Contributor
timestamp: December 20, 2020, 02:54:09 pm
content: I think the bar graph driver I.C. should haveworked for you although it only drives 10 leds.Their ladder can be used in such a way as tomeasure other than zero volts as the startingpoint. You could easily set up a 7 to 13 volt displayusing 10 segments. If you choose the linear displaydriver you would also know the exact turn-on pointof each segment. You can daisy chain the driversand end up with 20 segments for 7 to 13 volts.Just remember that at 10ma per segment youmay possibly consume 100+ma. Some of the driversused a scheme where each successive Led wasplaced in series with the first and the current neverwent above 10ma. Although these drivers useda VCC high enough for 10 leds in series and werefound in home consumer stereo type equipmentwhere +/-15vdc up to +/-35vdc power railswere common in the audio output section.