boatman

... and here is the component placement for the Power Unit at 2x scale. Link The big capacitors (C3 & C4) are 31.5mm tall and there is 33mm clearance between the top of the board and the case, so there should be no problem.

Most regulated 24VDC wall-warts have a positive on the centre pin. The only variation being either 2.1mm or 2.5mm centre pins. I think catering for negative centre pins and AC wall-warts is a step too far.

Actually that capacitor is too big so I've used this one instead. There's one for each ring so it should be sufficient. Revised schematic is here.

Sounds like good advice. This cap and this polyswitch seem to be ideal.

There is a slight modification to the Power Unit schematic. The two rings now have separate reverse-polarity protection diodes as the chosen device can only handle 3A and the total load for two fully loaded rings may exceed that. Schematic here Please note that there are also four mounting holes so that the board may be built into a desk easily. This was omitted from the earlier specification.

John - I've got a tecpro PS711 power supply sitting in the garage - you can borrow it if you want. (yes, I know there are plenty around, but I'm probably closest to John's island hideaway...) There's also some tecpro beltpacks, one with some BBC mods, and a LS411 loudspeaker station - let me know if they're of any use to you. Thanks for the offer but we made the decision to go with one male & one female for each circuit. A quick recap of the current spec: The Bluecom Power Unit will support two independent intercom rings and have the facility to common them. The unit will be designed to fit into the same enclosure as the beltpack There will be a male and female 3-pin XLR for each circuit. the connectors for circuit 1 will be on the front panel and those for circuit two will be on the back panel. The power will come from an external wall-wart 24VDC supply thus avoiding any need for certification of an internal power supply. The DC input connector will be fitted on the back panel and will accept external supplies with either a 2.1mm or 2.5mm connector with positive on the centre pin. There will be diode protection should a supply with a negative centre pin be connected. There will be a power indicator LED on the front panel. The circuits will be commoned by a latching push-button and there will be a second LED to indicate when the circuits are commoned. Link to schematic

Your wish is my command. I can't add attachments to this thread so they are elsewhere, but follow the links below. Schematic Component Placement The component placement is 2X actual size for easy measurement. C1, C2 & C18 are 0.2" pitch all other ceramic caps are 0.1" pitch.

Thanks Brian. In that case we'll stick with a male & female for each channel.

I don't have access to a Tecpro or Stonewood base station/power supply, so can those in the know tell me if they have a male & female pair for each circuit or two males. I haven't looked at one for quite a while and can't remember.

Yes, that's the one. The L272 has the same pinout and drive capability and could be used as a substitute. The drawbacks being that it's three times the price and its maximum supply voltage is only 28V against the 40V limit for the TCA0372. That will be fine with a base station having a regulated supply but may fail with older base stations which aren't regulated. The Bluecom Base Station will use an external 24V regulated supply so the L272M could be used in complete Bluecom systems. It just might be troublesome in older installations.

Further to the previous message, the PCBs have not arrived yet so it will be a few more days before we know that they are OK. We plan to offer kits of the "harder to get" components such as the PCB, case, XLR connectors and headphone amp (TCA0372). To avoid huge overheads, we will not include parts such as switches resistors and capacitors, which can all be obtained from Maplins, CPC, Farnell or RS, in the kits. We will provide a full parts list annotated with at least one set of supplier codes (probably CPC). we hope that Blue-Room members will contribute the part numbers from own favourite suppliers so that the final list will be acceptable globally. In addition to the above, The Blue-Room will be providing Gerber files for the main board and the front and back panels, so that members may have PCBs manufactured independently. Any comms system needs a base station/power supply and there will be a Bluecom base station design available. It will have two circuits which can run independently or joined. The PCB will fit inside the same case as the beltpack and use an external 24V wall-wart power supply. Using an external DC supply avoids any need for certification of final product as it will have no mains inside. There will be a male & female XLR pair on both the front panel and the back panel for the two circuits a DC input connector on the back panel, a latching push button switch to common the circuits and a couple of LEDs on the front panel. One LED will indicate the presence of power and the second will indicate that the two circuits are common.

The first batch of what we hope will be the final production board has been ordered and should be here very soon. We need to make a few tweaks to resistor values in the mic amp and hybrid circuits and then we can issue a final parts list. It's possible we will be able to sell a kit of parts, but it is unlikely that we will be providing ready-built and tested boards as there is too much speculative investment required. Thank you all for your patience.

I think Brian is back from holiday this week so we should have some comprehensive test results quite soon. After that we need to finalise the PCB layout and front & back panels so we can get some real boards made.

Those are only the first ten prototype boards. The design package being used is Easy PC version 16 and teardrops are easily added once the final track layout is complete. There's not much point for prototype boards as the tracking might change. Actually, it will as there are a couple of footprints which need modification and XLR connectors need to be moved. Also the board depth will have to be reduced from 80mm to 79.5mm as the case measures 79.75mm front to back and the PCB protrudes from the housing enough to cause a problem with the front and back panels. I will look at increasing annular ring sizes where it wont cause a design rule conflict.

We have prototype PCBs which, as you can see, really are blue! I don't know if they work yet, but the colour is right! http://mydesk.myzen.co.uk/_Useful/BlueCom/PcbFront.jpg http://mydesk.myzen.co.uk/_Useful/BlueCom/PcbBack.jpg I have spotted a couple of minor corrections required but they shouldn't cause it not to work.

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. 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.

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!

I should add that, at present, the changeover between dynamic & electret mics is a two pole DIP switch internal to the beltpack. One pole will add the bias voltage required by the electret mic and the second pole will reduce the gain of the mic amp. If people would prefer that the pack will work with either type of mic without having to fiddle with a switch, we may have to think a bit harder. A couple of other things which haven't been mentioned are: The mic switch will be a three position ON-OFF-(ON) toggle switch. The headphone amp will be a bridge configuration giving a considerable increase in headphone output over other systems.

Perhaps it's time there was an official Zero 88 upgrade for the floppy drives in the Frog series. There must be hundreds of these desks in schools all over the UK and very few of them are likely to be able to allow an unsupported upgrade to be done. If there was an official Zero 88 upgrade it would certainly be welcomed by many schools and community theatres.

Exactly, and that audio to the comms circuit would be the output from the mic on the sound desk. The external comms would come into the desk on an auxilliary input and be mixed with any other source as required. Hence the warning about not enabling the comms onto the main output bus. The OP would then use his normal desk headphones for everything.

Have you looked at the AD903 2-wire to 4-wire adaptor? It will allow you to interface the sound desk to the comms system. Just make sure you don't enable the comms on to the main output and you'll be fine.

Sorry, I stand corrected. I thought it was only the DMX versions that had PCB mounted fuses.

Any panel mount fuseholder for 32mmx6.3mm fuses will do the job. This is probably the closest match. Once you have opened an account with Farnell you can order anything with a credit card. Just remember that the prices don't include VAT, but carriage is free. Edited for spelling.