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AMBM - The Analog Meter Bridge Module Project

Modules as kits for DIY multichannel analog PPM or VU meter bridges

With LED bars containing 51 dual-color LEDs such a meter bridge is not only technically valuable but an exceptional eye-catcher, too

 

2 AMBM Dual Channel Module Sets (First Samples)

Contents

Videos

Watch (after a short introduction) the AMBM in action:

Higher resolutions than the video above (768 x 432, 25p, 164 MB, 2.5 Mbit/s) are available, but my hoster does not necessarily guarantee the necessary download speed so that you either should download it completely or wait a while befor you start viewing:

Medium resolution, (1280 x 720, 25p, 727 MB, 12 Mbit/s): The download is often fast enough

→ High resolution, (1920 x 1024, 50p, 1570 MB, 26 Mbit/s): The download is normally not fast enough

Features

What You Get and What Else You Require

The AMBM modules are meant to be kits, so you are not only free to install them in various ways - the drawback is that you also need to decide how to do it and to care for the necessary mechanical design and parts.

The kit contains:

That's it. No screws, no nuts and bolts, nothing else. Thus you have to care yourself for all these screws, nuts and spacer bolts, i.e., all mechanical parts.

And you must care for a power supply unit, e.g., 12 V, at least 350 mA per AMBM module set (2 channels).

Should you want to install the LED modules further away from the controller than the 45 mm IDC ribbon cables allow, let me know. I can alternatively supply the IDC ribbon connectors and sufficient cable separately.

Modules as Kits and Fully Assembled

The kits come with the SMDs solderered and tested, but you must solder the few THDs (trough-hole-devices) yourself. This allows you to assemble and wire them differently from my original intention and the description here.

 
The modules as they come as kits...
... and assembled with screw type terminals, pin headers and LED bars
The Control Module
AMBM-Ctl
AMBM-Ctl Kit
AMBM-Ctl Full
 
 
 
Two LED Modules
AMBM-LED
AMBM-LED Kit
AMBM-LED Full
 
 
 

Some Views of the Assembled Modules

  

 

The LED Scale

The AMBM's scale is identical for both VU and PPM. It reaches from -50 dB to +5.5 dB. 0 dB scale indication refers to either +4 dBu or -10 dBV (others are possible), which I think is widely used in non-broadcast studios. Levels above 0 dB are displayed with red LEDs, levels between -5 dB and 0 dB either yellow or green and all others LEDs below are green. The scale values are:

 When LED Nr. 
is lighting...
 ... the signal level is 
greater than [dB]
51
5.5
50
5
49
4.5
48
4
47
3.5
46
3
45
2.5
44
2
43
1.5
42
1
41
.5
40
0
39
-.5
38
-1
37
-1.5
36
-2
35
-2.5
34
-3
33
-3.5
32
-4
31
-4.5
30
-5
29
-5.5
28
-6
27
-6.5
26
-7
25
-7.5
24
-8
23
-8.5
22
-9
21
-9.5
20
-10
19
-11
18
-12
17
-13
16
-14
15
-15
14
-16
13
-17
12
-18
11
-19
10
-20
9
-23.33
8
-26.67
7
-30
6
-33.33
5
-36.67
4
-40
3
-43.33
2
-46.67
1
-50

Scale Lettering Template(s)

Maybe similar to this:

  or    or    or  

Anyway, yet to come...

+4 dBu, -10 dBV and other Reference Levels

Selection between +4 dBu and -10 dBV for 0 dB display is made by 4 solder joints (solder jumpers) on the solder side of the AMBM-Ctl.

Should you need another reference level for 0 dB display than +4 dBu or -10 dBV you can achieve it with 2 external resistors for each channel at its input pins, provided the reference level is higher than -10 dBV (= 316.2 mVRMS), read more below.

Operation

During operation you can change 6 settings with e.g. 6 switches. All modules can be controlled jointly by one set of switches or individually. All settings can be combined.

The settings in detail are:

Switch 1: PPM or VU measurements

PPM and VU measurements differ a lot from each other.

The PPM mode is selected as default, i.e., when switch 1 is off.

Switch 2: Bar display or dot display

 Bar display

 Dot display (dot color = yellow)

Switch 3, bar display: With or without peak hold

 Bar display with peak hold

(This is the default display, i.e, when all switches are off resp. when there are no switches)

Switch 3, dot display: Yellow or multi-color dot

 Dot display with dot color = background color

Switch 4: Background LEDs on or off

 Background LEDs off

Switch 5: Color pattern green-yellow-red or green-red

 Color pattern green-red

Switch 6: Display intensity high or low

 Display dimmed

DIY Aspects

Mounting

The LED modules can be mounted stacked on the control module using spacer bolts with a length of at least 30 mm, as shown on the photos here. When both LED bars are mounted this way, a pitch of either 21.59 mm (0.85") or 27.305 mm (1.075") is possible.

When the LED modules are mounted separately from the control module, a minimum pitch of 17.4 mm (0.675"), the width of the LED PCB, is possible. The LED module's PCB can be shortened by cutting or breaking it at the provided perforation.

The mounting holes are prepared for M3 (approx. #4-40 UNC) screws.

Should you want a huge distance between control and LED modules, you can also use very long ribbon cables. Up to 1 m is no problem. I provide ribbon cables with a length of 45 mm, intended for stack mounting of the module, as shown on the close-up view on the right.

The LED bars' protective foils are meant to be removed before they are finally built in. They are usually invisible but can produce reflections while the LED bars' surface itself is matt. Anyway, on all photos here you can still see the foils and, when you take a close look, reflections produced by them, too.

Wiring

Correct wiring is crucial.

Other Reference Levels

As mentioned above, when you need another reference level for 0 dB display than +4 dBu or -10 dBV you can achieve it with 2 external resistors for each channel at its input pins, provided the reference level is higher than -10 dBV (= 316.2 mVRMS). Connect these resistors in series with the AMBM's analog inputs. Each input wire requires one resistor. The values for these resistors can be calculated from:

R = (USource - UInput) × 42 kΩ/V

Example:

Contrast Filter Windows

I recommend to use a gray filter glass in front of the LEDs. That makes the display darker, but it enhances the contrast in illuminated environments significantly. With the photo on the right I tried to illustrate that, but it does not really show the effect in practice.

You can buy well suitable acrylic display windows from TTV GmbH, even in customized sizes. A gray color with a transparency of 30% is a good compromise. A scratch resistant and non glare surface is favorable. Such a material is ANTIFLEX-AR, which is usually in stock as ANTIFLEX-AR 1220 with thicknesses of 1.5, 2 and 3 mm.

Power Supply

The AMBM can be supplied with 7 to 15 V. The typical maximum average and peak supply currents are:

Supply
 voltage 
Maximum average
 current (all LEDs on) 
Maximum peak current
 (independent of LEDs) 
7 V
400 mA
500 mA
12 V
250 mA
320 mA
15 V
200 mA
250 mA

(Note: On the workbench, 5 V is possible, too, but with very little or no headroom for cable losses and tolerances.)

Due to the multiplexed LEDs there is a strong ripple on the supply current with peaks up to 25% more then the maximum average current listed above, even when not all LEDs are on. This is also why the AMBMs' grounds must not be connected to each other anywhere else but at their power supply inputs, preferably at the PSU.

Documentation

Pricing and Availability

This is a very new project. Currently I do not stock the module sets but I am prepared for production. If you are interested, please let me know. As soon as there are enough prospects (depending on the quantity one may be enough) I will start production.

AMBM kit, consisting of

 One kit  
 118.- € 
 Each additional kit*  
98.- € 
 Shipment Germany (DHL Paket)   
9.- € 
 Shipment other countries**  
15.- € 

  * A kit is regarded to be additional even when you order it somewhen later.
** Refer to How to order for details and excluded countries.

Let me know if you want single parts instead of 45 mm pre-fabricated IDC ribbon cables. And feel free to mail me for other questions.


Last update: November 13th, 2016 Questions? Suggestions? Mail Me! Uwe Beis