VU meter from scratch

Introduction

I remember how at the age of ten I first took up the soldering iron and by the age of fourteen I had already assembled a radio-controlled car, but with the advent of the computer I somehow abandoned this noble occupation. And now, literally two weeks ago, I was visited by the idea to make something beautiful. Thought and decided to make a VU - meter. I started digging forums on electronics, in search of the best, in my opinion, implementation of this device. After a day of searching, I came across an article in RadioHobby magazine, after searching a little more, I found a drawing of a printed circuit board. So, that neither logic nor the printed circuit board belongs to me, I proposed this scheme, as it is written in the magazine, Marcin Vyazan.

Here the fun begins ...
Caution traffic

This is a precision indicator of the sound signal level with an extended dynamic range and increased accuracy of the induced levels. The sound signal is fed to a precision detector made on the op amp U1, diodes D1, D2 and capacitor C6. The rectified and smoothed voltage from the detector output goes directly to the input of the driver IC of the U2 line of LEDs and through the divider R4R5, attenuating the signal by 5 dB, to a similar driver U3. The outputs of both drivers are interleaved so that their outputs of the same name in a common line of seventeen LEDs D3-D19 correspond to levels shifted by these very 5 dB (dB response levels on the circuit) are indicated to the right of the LEDs). Thus, an indication of signals with a level of -23 dB to +5 dB in steps of 1 dB for levels from -6 to +5 dB is provided. Together with the color coding (D19-D17 - red, D16, D15 - yellow, the rest are green), this construction of indicators provides convenient monitoring of the signal level near the nominal. The device is powered from a unipolar source with a voltage of 12 V. The integrated stabilizer IC U4 provides power to the line of LEDs and, through R6D20-D22, generates reference voltages of “artificial earth” for the op-amp U1 and drivers U2, U3. The sensitivity of the device is 0.775 V = 0 dB, the upper limit of the 22 kHz frequency range of

RadioHobby is 1/2008, s. 23-24

In general, the article is aimed at an audience of readers who have basic skills in working with a soldering iron and want to do something interesting, having practical application and not too difficult to implement. The article describes a bare test sample, in the future I plan to order Plexiglas with dimensions of 15 * 150 * 100 mm, there will be 20 pieces for each of the two channels, the blocks will be arranged horizontally. Each block will have 3 diodes. It should be something like VU - TOWERs.

Get to the point

PCB manufacturing

First we need to etch the circuit board. To do this, take a little money and go to the radio market, or another place where you can buy:

• Glass fiber single sided size 10 * 15 ( ~ 50r )
• Ferric Chloride ( ~ 60r per 100g )
• Glycerin ( ~ 40r )
• Lamond glossy photo paper 120 or 140 g / m ^ 2 ( ~ 200 rubles per 50 sheets )
• Acetone

We will produce a printed circuit board using the technology of the laser-iron method, or simply LUT. The technology is based on the fact that under high temperature the toner from photo paper is fixed on a foil textolite, while creating a protective pattern that protects the printed copper from chlorine poisoning.

After we stock up on everything we need, we can begin to manufacture the circuit board.

Download any program to open * .lay (I used Sprint Layout 5 ) and download the board project .
We print the board image on the laser printer, while it is desirable to indicate high contrast and print quality in the printer driver settings. Also in Sprint Layout we remove the layer with the signatures, and set the color of the tracks to black. It is necessary to print in mirror image. It is advisable not to touch the paper with your fingers on the surface, so as not to leave greasy spots on it.





After printing, carefully cut it out and put it aside.



We take fiberglass already cut to the required dimensions (115 * 45 mm), grind with a fine sandpaper, and remove greasy stains with acetone or nail polish remover.



Next, we apply the print with the toner down to the fiberglass and very carefully iron it with an iron at maximum temperature. This is a very important point, it is necessary to iron every corner, every square millimeter of paper. Iron until the paper turns slightly yellow. It took me about 5 - 7 minutes.





Let the board cool for 5 - 10 minutes, and substitute under a stream of water. With gentle finger movements, we roll the paper until it is completely separated from the plate. At this stage, it is important to check the quality of the print well, because if there are places where the toner has not been printed, they will be erased out and the contacts will be broken. If everything is bad, then repeat the process, if there are small shoals, then gloss over them with a marker.





Next, we prepare a solution of ferric chloride in water. Usually 100 g of powder is enough for 0.5 - 0.7 liters of water. Pour the powder into water, and not vice versa, in small portions, since the reaction proceeds with the release of a large amount of heat. By mixing, bring to a uniformly rusty color.



Gently at an angle we lower our board into the solution, hold for some time periodically checking how the process is going. On average, the etching process takes from 10 to 40 minutes.











When all unnecessary copper is etched, we take out the board and rinse under running water. Next, we carefully consider the board for the presence of copper residues and gaps. If there are none, then everything turned out fine and the circuit board is almost ready. There is very little left. Again we take acetone and carefully remove the toner from the board with a swab.





You can start drilling. Since I do not have a drill, like other precision tools, I used a conventional construction drill.





Next, we need to tin board. We put the soldering iron to warm up, and for now we take a cotton swab, we dip it in glycerin and apply a layer to the board. When the soldering iron warms up, we take a bit of solder with a sting and go through all the tracks of the board. It is better to cover all the tracks with tin to prevent copper oxidation and to be sure that contact is not broken anywhere. Then we wash the board from glycerol under running water and let it dry.













So the circuit board is ready. Now you can start filling it with electronic components.

Filling the board with filling

Shopping list

• IC LM3916N-1 PDIP18 * 2pcs (~ 100rub each)
• 78L05 voltage stabilizer - 1pc (~ 20r) *
• Diodes 1N4148 (KD522A) 150mA, 100V DO-35 * 5pcs (~ 1p each)
• The operational amplifier TL081 PDIP8 - 1pc (~ 20r)

Capacitors:

• K10-17A N50 0.1mkF * 2pcs (~ 5r)
• K10-17A N90 0.33uF - 1pc (~ 5r)
• K50-35 47mkF 16V * 3pcs (~ 5r)
• K50-35 470uF 16V - 1pc (~ 5r)

Resistors

• 330 ohm
• 2.2 kOhm
• 3.0 kOhm
• 3.9 kΩ
• 47 kOhm
• 120 kOhm
• 10kΩ tuning resistor, I took 3362-1-103 (~ 20r)

The price is a penny. (Unless, of course, buying them in Chip and Dip)
I took C1-4 0.25 watts went perfectly, take each of 5 pieces, the extra ones will remain fearless, it is better to have more supplies than to go shopping around the component again because of a broken leg.

* As for the voltage regulator. Initially, I soldered the circuits to 78L05, it was very hot after switching on, the stabilizer was designed for 100mA, the consumption of diodes was much higher, so I replaced it with the LM7805 in the TO220 package, which is already rated for 1A and mounted a radiator on it. So if the diodes are with a large amperage, then I advise you to take care of the stabilizer.


Also, if you wish, you can take care of the sockets for microcircuits, because to solder microcircuits in the event of a malfunction is quite problematic.



I think the process of soldering does not need an explanation, so I offer you just photos without comments.























Demonstration of a working sample



And another video, already two assembled drivers

Conclusion

In general, the assembly took about one evening, the price is about 600 rubles, taking into account the cost of the diodes. How to use this device depends on your imagination, I told you about my idea, I think this driver will fit in well with the subwoofer in the car and any speaker system. In addition, this driver has 2 signal level display modes: BAR and DOT. To switch them, it is necessary to close or open the contacts indicated on the S1P / L circuit board. I especially liked the implementation of this device using plexiglass, when 10 - 20 mm thick blocks are cut and a diode is inserted into each block. It looks very beautiful.

I would also like to add that this is part of one large project to build a home audio system which will include:

• External USB DAC
• Graphic equalizer for 10 * 2 bands
• Spectrum Analyzer 20 * 20
• Amplifier with tone block on encoders
• And much more, exclusively do it yourself

Now I am engaged in PCB layout for a spectrum analyzer . To whom it becomes interesting, I will gladly share all the collected information on this topic.