[TIDY] restructure readme
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README.md
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README.md
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@ -38,13 +38,16 @@ All inputs (besides the microphones) and outputs should:
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This results in a signal flow like this: 
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## Status
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### Tasks
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- [x] Requirements collection
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- [x] Electrical design draft/ proof of concept (breadboard)
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- [x] Proof of concept validation
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- [x] First PCB layout
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- [x] First PCB layout (prototyping modules)
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- [x] More testing/ validation
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- [ ] Second PCB layout + casing prototype
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- [ ] More testing/ validation
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Help is always appreciated!
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@ -56,27 +59,28 @@ Help is always appreciated!
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- [x] Adjustable headphone mix and output volume
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- [ ] ESD protection and galvanic isolation of line inputs and outputs
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- [x] VU meter (own PCB)
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- [ ] VU meter (integrated in front panel PCB)
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- [ ] Mute and On-Air buttons
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## Electrical Design
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This chapter contains some notes on the electrical design.
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Currently just the sources of the used circuit designs.
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### Sources and Design Considerations
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#### Microphone Input
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##### Preamplifier
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### Microphone Input
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#### Preamplifier
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For the microphone preamp, we are using the NE5534 low-noise opamp with a circuit design from [circuitlib microphone pre-amp](https://www.circuitlib.com/index.php/schematics/product/29-balanced-microphone-preamplifier).
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##### Controllable Amplification
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#### Controllable Amplification
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In a normal mixer, you would be able to lower the microphone's volume to zero.
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But in our case we just need on/ off and some gain range to adjust for different microphones and loudness of different people.
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TODO: Integrate the On-Air button with it's LEDs
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#### Line Input/ Input Module
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### Line Input/ Input Module
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The line input must not be amplified at all, because loudness control of the headphones is done by the headphone amplifier section.
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But the differential line-level signal must be converted to a single-ended signal by the input stage.
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@ -85,7 +89,8 @@ The second part of that circuit was taken from the [circuitlib audio mixer tutor
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TODO: How to achieve galvanic isolation?
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#### Summing
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### Summing
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Summing is needed in two places: Creating the sum of all microphones (not adjustable, fixed output gain) and for the headphone mix (one input level adjustable).
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A simple summing circuit using one operational amplifier is enough for our application, like in [circuitlib audio mixer tutorial](https://www.circuitlib.com/index.php/tutorials/product/39-how-to-build-an-audio-mixer).
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@ -95,21 +100,33 @@ In our case, there are just two types of summing: All microphones for the interp
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Because the stage input is quite independent of the interpreter's microphones, no special phase/ inversion considerations are needed.
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And the microphones connected to our unit will experience the same inversions anyways.
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#### Line Output Driver
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### Line Output Driver
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Line Output conversion is done by the [DRV134](https://www.ti.com/product/DRV134) IC.
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TODO: How to achieve galvanic isolation?
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#### Headphone Output Driver
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### Headphone Output Driver
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The headphone output needs a maximum output power of about 0.1 W and should put the mono signal on both stereo channels of the TRS jack.
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For the first draft, we're using one LM386 audio power amplifier even though it has a quite high minimal amplification of factor 20.
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#### VU Meter
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### VU Meter
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When searching for VU meter circuits, many use the LM3916 LED bar graph driver, which already has the right scaling built in.
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But this chip is obsolete and not produced any more, so we designed our own chain of comperators to drive a set of LEDs.
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#### User Interface Hardware
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## User Interface
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The user interface should enable the interpereters to adjust their microphone gain and headphone mix on their own.
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Additionally, a (permanent) on/off switch, as well as a (temporary) mute button should be present.
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A possible UI layout might look like this: 
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### Potentiometers
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After some long research to find single and dual channel, logarithmic scale potentiometers with the same dimensions, there are only a few options left:
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1. Alps Alpine Series RK09K/D, 10 kOhm (log), 15 mm length, vertical mount: RK09K1130AJ3 (single) and RK09K12C0A19 (dual)
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6 mm D-style (4.5 mm) shaft, 6 mm flattened + 2.2 mm (incl. 0.8 mm collar) = 8.2 mm from top
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@ -125,15 +142,17 @@ Notes: More expensive than RK09K; Thread should fix 2 mm front plate well
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Notes: Quite long shaft, matching knobs difficult to find
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Possible knobs may be:
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- Rean F311/ F313 series (11/ 13 mm diameter): 9 mm hole depth (no skirt/ flush with end of flatted axis section)
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- Rean F311/ F313 series (11/ 13 mm diameter): 9 mm hole depth (no skirt/ flush with end of flattened axis section)
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Notes: Will fit option 1 (and 2, if potentiometer placed accordingly)
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- Rean P670 series (12 mm diameter/ 16 mm at bottom): 7.5 mm hole depth + 4.5 mm skirt = 12 mm
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Notes: Should fit option 3
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- Cliff K87MAR series/ RS Pro 777-73xx: 7.5 mm hole depth + 4.5 mm skirt = 12 mm, inner size of skirt 12 mm (measured)
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Notes: Should fit option 3 (boring for potentiometer nut a bit tight); Size quite like Rean R670
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Notes: D-style boring has wrong size (5 mm instead of 4.5 mm flatted)
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- Rean P300 series (11 mm diameter/ 15 mm at bottom): 9 mm hole depth + 3 mm skirt
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Notes: Might also fit option 3
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### Switches
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The On-Air button needs to be a latching SPST (or SPDT) switch with LED illumination, like:
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- E-Switch LP11EE1NCSYG
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@ -143,11 +162,13 @@ The mute button needs to be a momentary SPST (normally open) or SPDT push button
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- TE Connectivity PB6B2FM3M2CAL00
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- TODO: other, less expensive options highly appreciated!
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### Casing
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The casing should be a desk console (angled surface), ideally with space at the front to mount the headset ports (XLR and 6.3 mm jack), like:
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- [Bopla ATPH 1865-0250](https://www.bopla.de/gehaeusetechnik/product/alu-topline/alu-topline-gehaeuse/atph-1865-0250.html) (front might not have enough space for the connectors)
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- TODO: other options appreciated
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- Or laser cut/ 3D print something
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A possible UI layout for the Bopla ATPH 1865-0250 might look like this: 
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## Notes
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@ -164,13 +185,13 @@ Approximate prices in Euro.
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Connectors and Buttons (User Interface)
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| Count | Manufacturer + Art. No. | Description | Price |
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| Count | Manufacturer + Art. No. | Description | €/ pc.|
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|-------|--------------------------|----------------------------------|-------|
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| 1 | Neutrik NAC3 MPA-1 | Mains Power Input | 3.33 |
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| 1 | Neutrik NCJ 6 FAH | Line Input | 1.27 |
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| 1 | Neutrik NC3 MD-LX | Line Output | 3.22 |
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| 3x1 | Neutrik NCJ 6 FAH | Headset Microphone Input | 1.27 |
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| 3x1 | TODO | Headphone Output | TODO |
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| 3x1 | Rean NYS 216 G | Headphone Output | TODO |
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| 3x1 | NKK UB15NBKW01N-C | Mute Button | 7.50 |
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| 3x1 | E-Switch LP11EE1NCSYG | On-Air Button | 5.00 |
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| 3x1 | Alps RK097111080J | 10K log Mono Pot. (Gain) | 2.16 |
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@ -183,13 +204,13 @@ Connectors and Buttons (User Interface)
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Sub-Components
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| Count | Manufacturer + Art. No. | Description | Price |
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| Count | Manufacturer + Art. No. | Description | €/ pc.|
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|-------|--------------------------|----------------------------------|-------|
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| 1 | Traco Power TXL 035-1515D or TOP 60533 | Power Supply | ~48.00 |
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PCB Components: TODO when schematic is finished
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| Count | Manufacturer + Art. No. | Description | Price |
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| Count | Manufacturer + Art. No. | Description | €/ pc.|
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|-------|--------------------------|----------------------------------|-------|
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| 3 | NE5534 | Low-noise Op-Amp | 0.54 |
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| 8 | LM833 | Generic Op-Amp | 0.88 |
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@ -202,7 +223,7 @@ PCB Components: TODO when schematic is finished
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VU Meter Components
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| Count | Art. No. | Description | Price |
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| Count | Art. No. | Description | €/ pc.|
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|-------|---------------------|---------------------|-------|
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| 1 | Vishay M64{Y,Z}503 | 50K Trim Pot. | 0.95 |
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| 1 | LM833 | Generic Op-Amp | 0.88 |
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