2-Pack VU Meter Boards with Driver and Warm Backlight for Audio Level Monitoring and Recording

This product did not come with any specifications or data sheet. But to be fair, somebody who would be interested in buying this probably knows enough to figure it out for themselves. The meters are cuter than a bee's knees and the circuit board is nicely laid out. An explanation of each connector is silk-screened onto the board. The hole for the meters has to be fairly precise as there is no flange to hide the edge. Fortunately, I had a chassis punch of exactly the right size. The meters looked a lot better loaded from behind.My application was wanting to monitor audio being sent to and being received from a computer. The computer is running Zoom teleconferencing software. We have a conference room with 16 microphones and a distributed speaker system in the ceiling. We desired to have all the microphones routed to Zoom, and have receive audio through all the speakers. NOTE: There is more to making this interface work properly. PC's route microphone audio out to the headphone. This is called side tone. This audio pathway wreaks havoc in an audio conferencing scenario by creating echos. Audio being transmitted is routed back to the room and heard on the speakers. It is a deal killer. My solution is to use an acoustic echo canceler to remove side tone. The transmit signal to the computer is also routed to the echo canceler, to which the receive audio is wired. If you know how to program ClearOne, Biamp, Soundweb etc. then this explanation is all you need to know. I've been doing this for 10 years or so, since PC's started getting conferencing software. It really works well. I think Extron recently came out with a product to do this same thing, which, I imagine, is a single channel echo canceler in a box. I just use one in the DSP box.The purpose of this project was to allow checking levels to and from the computer. When something happens and audio is lost on a Zoom call, being able to check for signal to/from the far end helps narrow the problem down. Is it in the room, or is it related to the far end.Audio to and from the room sound system is line level balanced. The run is 50' long. A Radio Design Labs STA-1 two channel buffer amplifier is used at the computer for receiving and driving the long wires.Since no instructions came with the meters and driver board, I had to make some assumptions, starting with, what kind of power does the board need? Tracing out the parts on the circuit board, incoming power, AC or DC was not specified, first lands on a full wave bridge rectifier, gets filtered, and lands on the input of a standard 7812 3 pin regulator. Since I already have 24 VDC for the Radio Design Lab, I wondered if the meter driver board would work on DC. It does, in fact. For testing, I input 15 VDC, a level that gives some headroom for the 7812. The integrated circuit on the meter board is a BA6138 which is a "square law compression amplifier." It is specifically designed for driving meters. I did not know this, so poking around the circuit board and looking up datasheets on parts really paid off.The meters are nicely illuminated. A single SMD LED per meter does the job. In my application, next to a monitor, I thought it might be a little bright. So I wired the LEDs in each meter in series. It is a warm white color, just about exactly what you would expect from an incandescent bulb being run on slightly less than rated voltage for long life.I applied a .775 volt RMS sine wave at 1 kHz and used the trim pots to adjust the meters to read 0Db. In actual use, I'll adjust the trim pots to put the average level around zero, irrespective of what the signal actually is.Looking up the acceptable input voltage range to a 7812 regulator, I found it was good to 35 volts. So I am running the meter driver board of a 24 VDC wall wart. The 7812 barely got warm to the touch.This was a nice little project. I'm going to buy another one! Not sure what I'll meter, because I retired 18 months ago, from a career in commercial audio and communication systems.

It’s pretty cheap plastic and very small but it looks like it’ll do the job no problem at all if only they came with instructions. This has nothing to help with the installation at all. Lil disappointing.

It works very good, kq4lxg