Attempting to build a Mic/Line tester with a LED VU meter, and Tone generator/Oscillator

Discussion in 'The Projects Forum' started by steveblurr, May 10, 2019.

  1. steveblurr

    Thread Starter New Member

    May 10, 2019
    This is my idea for my first electronics project. I'm having a hard time trying to figure out what I need in order to make this happen. I am looking for reading material, equations, design concepts in order for me to achieve this.

    Since I work in television, I've used a Q-BOX for years now. The other day I was repairing some equipment and realized I have not done any DIY project or used my basic electronics 'skills' since I took courses in college. Then I realized, wouldn't it be cool to make my own tone generator and mic/line tester? So I've been doing some web browsing and I found some articles and schematics but I'm not too sure if they cater to me.

    I was wondering if anyone can point me into the right direction to my concept below:

    Mic/Line Level - IN : it would be a XLR-F for input with a visual LED VU meter (LM3916 or LM3915), what would I need to have 20 LEDs?
    Pretty much I am going to be taking the LINE out of given device into this box and testing levels. A gain-control POT would be nice to setup level (thinking of a gain/trim pot from a mixer to set my level to 0dB). Same idea but with the option of adding a 1/4 jack, so I have the option of going XLR and TRS in (balanced and unbalanced)

    I know there is an impedance difference between MIC/LINE level - so I'm not sure if I can use the same circuit or if I need a switch in order to select when I'm going Line In or Mic In - I know mixers have different input jacks. I want to go the same route if that's standard.

    Tone generator/Oscillator - Would love the option of messing with the waveform (Sine, Square, Triangle) - Maybe just sine and square, or maybe just a sine wave. I wouldn't mind just having the options to switch over to have fun with this box. Tone generator would need a level POT to control the output level. I've read that people add a frequency selections involving 250HZ, 500HZ, and 1kHZ. I would love that. Just to go that route.

    This is pretty much want I want in this box at the moment. It will be traveling with me when I work shows and what not. Would love to see if I can get pointed into the right direction.

    I've never designed a circuit before. Just used schematics that I've found. I don't have experience with design and math equations (I know OHMS law though) but if I can get anything from you guys, I am entirely grateful.

    Thanks for reading.
  2. MrChips


    Oct 2, 2009
    Welcome to AAC!

    Sounds like a good idea and a splendid way to dabble into some electronics.
    Many years ago before digital became the norm I repaired a lot of radio and TV on the road and always dreamed of building a portable test bench in a suitcase.

    My first question to you is about portability. Do you need battery operation or is AC mains as your power source acceptable?

    The test equipment of choice would be an oscilloscope and function generator. With today's technology, you can have both in a smartphone.
    Have you considered this possibility?
  3. steveblurr

    Thread Starter New Member

    May 10, 2019
    Maybe batteries will work. I want to for this in a small enclosure. Think like a pedal box of some sort. I’ve made guitar pedals in the past so I’m thinking of using a similar concept in terms of size and portability. I just don’t know if I’ll be able to fit everything in a PCB.

    I’ve done smartphone applications but I would prefer having a physical device that I made myself etc.

    My struggle is approaching this in a math way. I have the idea and drew out my plan I just don’t know where to start my calculations. And which resistor values/capacitors I need. Or if I should use an Op Amp (TL702) or what? This is my setback right now.

    Thanks for replying!