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BlueClone - The Blue Room's Own Comms System


Brian

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On a similar line to dbuckley's suggestion, would it be possible to add a couple of terminals (could be just solder pads) in the audio path after the mic pre amp and also in the output stage before the headphone amp? It'd mean you could use the same pcb to make a master station with line in and out. It'd also give options in the future for building 2 channel master stations and beltpacks just by strapping a pair of pcb's together with suitable buffering. Not something I'm suggesting you'd design, but it'd give a little assistance to the DIY'er who was using them as a starting point.

 

2 sockets in parallel is a nice touch. I hate soldering tinsel wire (he says looking at the box of 16 radio mic headsets all needing reterminating) and whilst I've grown pretty good at them over the years and I think a 4 pin XLR is infinitely better, I take the point that it's probably more hassle than it's worth changing the plug on a cheapo headset, especially as the factory fitted moulded plug is probably far better than I'll ever manage with my soldering iron.

 

As an aside, and whilst I understand this is an open source project and really appreciate you're making all of this available for free, I really wouldn't mind a few quid heading in to your pockets for the work you've done! Maybe if that's difficult you could set up a donate function so happy users can send a bit of a thank you? Might only be beer money from some, but I'd consider it a very worthwhile thing to do.

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Thinking out loud, I'd be concerned at the noise level of some toggle switches (the actual noise of operating the switch) - in a quiet scene for example, the CLICK-CLICK of the switch going on and off...?

 

But then, is this any different to the Tecpro style switches? Probably not? :)

 

I've always been a fan of the "smart" Clearcom buttons with the double tap to latch, but I appreciate that this is probably outside the scope of this project, so I digress :)

 

Looking good, and another +1 for David Buckley's suggestion of the audio in and out, for a DIY radio interface or whatever

 

David

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How about doing the mic switching with a picogate D type or similar, so that a short interruption to the power from the master station can be used as master 'mic off' command from the prompt desk? I believe some of the Clearcom kit does something like this and it is usful when some muppet leaves a mic on and walks away.

 

Also, some compression and/or noise gating? Possibly just a jfet across the mic line with fairly simple minded feedback?

 

Could we have an option to put a fixed resistor in line with the bottom of the volume control so it is not possible to take the headphone volume all the way to zero by accident (Hate to say it but I have missed a cue due to that one).

 

Final thought, if the signal lamp control voltage were to be defined as on say between 1/2 and 3/4 and off between 1/4 and 1/2 of the supply voltage then it would be possible to implement a red LED to indicate a shorted or pin 2/3 reversed line, that would save a lot of fault finding pain on occasion (A confidence LED on the front would be good). The 1/4 supply would be provided by the power supply via the terminating network so any cable short or open could be detected by the outstation and some faults could be picked up by the master station. I think this would probably be backward compatable.

 

I have access to Altium 10 and would not mind getting involved in the design if that toolchain matches what you guys are using.

 

Regards, Dan.

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Just a quick reply to some of the points...

 

Even if you manage it the joint is fragile. Keeping the jacks is probably more reliable.

 

My thoughts entirely. Plus, the cable itself is usually quite thin and doesn't play nicely in XLRs. Ironically, sticking with the moulded 3.5mm plug will probably be more reliable.

 

 

could audio in and out be provided on unpopulated pads on the PCB so as to make the incorporation of the PCB into non-conventional applications easy, sort of a halfway to the AD903?

 

Probably. We'll look at squeezing a 0.1" pitch header onto the board. But see next reply as well.

 

 

It'd mean you could use the same pcb to make a master station with line in and out.

 

The AD903 has transformers in and out. Our output stage is already a high-current design which means it would quite happily drive a transformer. A change to a couple of resistor values in the mic amp would make it a line level input which could be fed from a transformer.

 

All this means it would be easy to make a version which has fully isolated 4-wire connections. This could be as simple as a little box, containing two transformer which plugged into a modified pack.

 

 

I've always been a fan of the "smart" Clearcom buttons with the double tap to latch, but I appreciate that this is probably outside the scope of this project...

 

 

IIRC Clearcom use a custom IC to do all the mic and call logic which runs off the Vbias supply (ie half DC volts) without any regulation, it is then capable of driving all the FETs etc without any level shifters.

 

 

How about doing the mic switching with a picogate D type or similar, so that a short interruption to the power from the master station can be used as master 'mic off' command from the prompt desk? I believe some of the Clearcom kit does something like this and it is usful when some muppet leaves a mic on and walks away.

 

See reply above about Clearcom. Doing it with 'conventional' parts will add quite a few components.

 

 

Also, some compression and/or noise gating? Possibly just a jfet across the mic line with fairly simple minded feedback?

 

We'll take a look. It depends a bit on board space.

 

 

Could we have an option to put a fixed resistor in line with the bottom of the volume control...

 

Don't see a problem with that.

 

 

...if the signal lamp control voltage were to be defined as ... I think this would probably be backward compatable.

 

I'm not sure it would be. As part of this project I've studied every comms pack I could get my hands on and they vary enormously in how they drive and receive the call lamp.

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Perhaps not so much for the theatre folks, but what about pads at least to add a buzzer/siren like the ASL kit has on the call light; it's really useful in a loud environment. I guess likewise, some simple way to add a relay or similar to fire a Xenon to make a strobe call light.
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Can I also suggest that the design be made using "Chunky Trax" technology with all tracks made at least 1mm thick to make the ultimate design more serviceable. If the schematic is fairly simple then the few links on a single sided PCB are a small price to pay for the extra serviceability of a single sided board. It does usually mean more manual routing though. I know the cost difference between single sided and double sided is minimal, but anyone who services PCBs knows the benefits of single over double when it comes to swapping out components or hacking.

 

I've never really understood PCB designs where the tracks were all the thinnest possible regardless of actual space on the PCB. The Elektor PCB designs used to be like that.

 

Moderation: Moved from a different topic to here

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At the request of BR members the following additions have been made:

 

A resistor has been added at the low end of the headphone volume control.

 

A 6-pin Molex KK polarised connector has been added with these connections:

 

1 - MIC_IN

2 - GND

3 - MIC_OUT

4 - HYBRID_OUT (== Headphone amp in)

5 - HEADPHONE_OUT_+

6 - HEADPHONE_OUT_-

 

I will now attempt to fit everything on to the 100mm x 80mm PCB to fit in the chosen enclosure!

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This all sounds terrific.

 

Can I make a couple of late suggestions?

 

Could the mic gain be adjustable, even if, like is common for side tone rejection, it is via a trimmer. Last week we were at Minack where they had a mix of canford cans and ASL cans and the mic levels seemed to be quite different.

 

Instead of a "siren", a vibrator as found in mobile phones might be a better alternative.

 

However, as he design stands , it still sounds excellent, and you are to be congratulated and thanked for such a fine effort.

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It mentions adjustable mic gain in the first post. I was very pleased to see it there as I've had just the issue you describe, specifically between the new plastic ASL packs and Metro/Stonewood (and now Granite!) systems.

 

Vibration motors are surprisingly cheap. Como Drills make them and I've used a couple in a project recently. Worked really well. They'd probably run off of the lamp circuit happily enough as they require very little current, though they also only run on something like 3V, so a bit of tweaking required.

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It mentions adjustable mic gain in the first post. I was very pleased to see it there as I've had just the issue you describe, specifically between the new plastic ASL packs and Metro/Stonewood (and now Granite!) systems.

 

Yes, I noticed that and thought it meant it was switch selectable i.e. high gain, no bias voltage for dynamic or lower gain and bias voltage for condensor. Brian and Boatman can no doubt clarify. Continuously variable would be nice if it wasn't a problem.

 

The Canford cans we were using looked remarkably like Stonewood ones, AIH.

Edited by alistermorton
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.

Could the mic gain be adjustable, even if, like is common for side tone rejection, it is via a trimmer. Last week we were at Minack where they had a mix of canford cans and ASL cans and the mic levels seemed to be quite different.

.

 

.

It mentions adjustable mic gain in the first post. I was very pleased to see it there as I've had just the issue you describe, specifically between the new plastic ASL packs and Metro/Stonewood (and now Granite!) systems.

.

 

The current design has two mic amp gain settings which are switchable with one half of an internal 2-pole DIP switch. The other pole switches on the bias for electret mics. I'll see if it's possible to add a mic gain preset as well, but we are getting quite crowded on the PCB already.

 

 

.

Instead of a "siren", a vibrator as found in mobile phones might be a better alternative.

.

 

.

Vibration motors are surprisingly cheap. Como Drills make them and I've used a couple in a project recently. Worked really well. They'd probably run off of the lamp circuit happily enough as they require very little current, though they also only run on something like 3V, so a bit of tweaking required.

.

 

I don't think anyone ever mentioned any inhabitants of Sirenum scopuli, but the LED call light indicator will have a constant current source set at 20mA. If that current is suitable for a vibrating motor then a link in series with the LED could be added to the PCB. That would allow an optional vibrator to be fitted or the link shorted if it's not required. I doubt we will have space for a separate 3V motor drive circuit.

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