Mechanical Design

[TerryJC]

To start this Topic, I will lay out a few design aims. The Equipment Case provided by Penri has an unfettered internal area approximately 170 mm x 180 mm or 220 mm x 110 mm (depending on the orientation of the baseboard). If the maximum amount of the space is used then this increases to approximately 170 mm x 220 mm, but the corners of the baseboard will need to be shaped to fit the internal profile of the box.

I have a number if ideas for how to build this:

1. A shaped perspex, plastic or plywood baseboard that utilises the maximum amount of the space available. Components will all be mounted on pillars and there will need to be a small Veroboard to accommodate the Low Pass Filter. This may be necessary if space becomes short, especially if the 12 V PSU Brick is to be accommodated inside the case.
2. As above but without cut-away corners. This may make it easier to accommodate the PSU Brick since it could be fitted under the baseboard, but the total real estate is reduced.
3. Everything mounted on a big sheet of Veroboard apart from the PSU Brick. We don't need the interconnectivity, but I already have a 100 mm x 160 mm sheet and this size can be purchased for approximately £4 on eBay. However, we would probably need a second smaller sheet for the Pi Zero, unless a larger sheet of Veroboard can be sourced cheaply.

So before I commit to a method, I need some feedback. The answer to the following questions will inform which approach is likely to be the best.

1. We need to agree connector types. I've already raised this in viewtopic.php?p=4479#p4479 and viewtopic.php?p=4493#p4493.
2. Where do we want the connectors to be located? Logically, there should be connectors on the top surface of the box for the Tower equipment and the Antenna. We could also bring the Speaker connectors out there and we'd also need to get power in. However, if we put the connectors on the top of the box, they may be too difficult to access.

Any other ideas would be welcome.

[Penri]

Hello

Shaped perspex, plastic or plywood baseboard

I can provide any of these, cutting out the basis shape, with or without cut-away corners, is something I can do at home. Drilling a hole pattern if you can provide the "drilling drawing" is also within my skill set. I need to check but I think I have an identical case in the workshop to use to size what's required.

Plywood is the easiest to work with and most readily available, plastic / perspex would have to be 4mm or so to have the necessary stiffness and can be a little tricky without sharp tools plus I'll have to check what we have at hand. Personally I wouldn't use the vero board, more because the other material is more cost effective (I think).

I need to re-check the space available in the bell tower but my preference would be to mount the case on the tower wall and bring the connections out through the bottom of the case so any water topping on case won't get to the connectors.

I'll get back to you on my thoughts on the connectors later, I have another matter to attend to now

[TerryJC]

Plywood is the easiest to work with and most readily available, plastic / perspex would have to be 4mm or so to have the necessary stiffness and can be a little tricky without sharp tools plus I'll have to check what we have at hand. Personally I wouldn't use the vero board, more because the other material is more cost effective (I think).

That would be really helpful. Since I posted the query I've been thinking about this and have come to some conclusions:

1. I think a full shaped baseboard would be best and I've been trying to make a template based on a scan of the inside of the box. I'd like the maximum size if possible, which means that the corners would need to be contoured to fit.
2. If we make the contoured baseboard, I would mount it on longish pillars and fit the existing PSU Brick beneath it (it is a 5 A type, which should be enough). It may be necessary to leave enough space on the bottom edge of the baseboard to bring out the DC wiring.
3. I have made a crude paper template and think that there is plenty of room for all the components providing that the PSU is out of the way.

I need to re-check the space available in the bell tower but my preference would be to mount the case on the tower wall and bring the connections out through the bottom of the case so any water topping on case won't get to the connectors.

The Equipment Case should be oriented in landscape mode to allow room to put the two Pis side-by-side. This would also leave lots of room at the bottom for the connectors.

I'll get back to you on my thoughts on the connectors later, I have another matter to attend to now

If we go with the above, then one of the connectors would need to be capable of carrying mains.

[Penri]

Terry

I'll make sure I have material today and do the cutting out etc. over the weekend.

In the case of the mains feed, if that goes directly to a 13amp plug then I'm happy with it being a flying lead through a grommet.

What I want to avoid, when removing the box, is having to remove wiring attached the building. The connectors don't need to be bulkhead mounted, although they do look neater, as long as they are easy accessible and not too fiddly to deal with.

[TerryJC]

In the case of the mains feed, if that goes directly to a 13amp plug then I'm happy with it being a flying lead through a grommet.

That might be a bit difficult unless we chop the 3-pin plug off and add another after the wire has be routed. Both ends are moulded.

All doable though.

[Penri]

Terry

I have created a couple of interesting plywood insert shapes for the case. I made the two so one can be screwed to the base of the case and the other mounted off it on pillars.

I have also surveyed my stock of IEC mains leads (assuming that's what is needed), I have lots.

When would you like mr to deliver?

[Penri]

Just reviewed the Minster electronics diagram and now realise that I've made the wrong assumption and it's the 12V side of the PSU brick that's routed into the electronics box.

The final question should read, when would you like me to deliver the ply shapes?

[TerryJC]

Just reviewed the Minster electronics diagram and now realise that I've made the wrong assumption and it's the 12V side of the PSU brick that's routed into the electronics box.

I've now modified the diagram to bring the mains in through a grommit, which means that I will fit the PSU inside the case (under the baseboard).

The final question should read, when would you like me to deliver the ply shapes?

Any time you like apart from the two periods each day that I told you about before.

[TerryJC]

I have completed the first draft design for the mechanical layout and have attached the two drawings that show where the modules will be mounted and the layout of the small Veroboard circuits that are needed.

This proved to be more 'interesting' than I expected, because the various Adaptors and their associated cables are actually physically larger than the major electronic modules. In the end I decided to use both of the baseboards that you made Penri; The lower baseboard will support these adaptors and the wiring and the upper baseboard will then have plenty of room for the Pis and the MOSFET Drivers. The upper baseboard will have two fairly large cutouts so that the cables and wiring can be brought through from the lower baseboard.

In keeping with this, the two connectors for the incoming power and for the WiFi signal will be mounted so that the wiring from them emerge in the bottom space and the audio and solenoids connectors will be mounted so that the wiring from them emerge in the upper space.

Now that we are using 12 V DC for the power, I have included a 10 A barrel connector rather than the grommet with a hanging mains lead as originally envisaged.

[TerryJC]

I have now completed the construction of the equipment (photo below). There is still some wiring to complete and the Bells half of the system has not yet been tried, but I believe that this design will be sufficient so have included the latest version of the Circuit and Mechanical Design Drawings.

Minster_Bells& Player.jpg (177.91 KiB) Viewed 704 times

As can be seen from the photo I had to do a bit of head scratching to make it all fit and be reasonably neat and maintainable. To accommodate the stiff USB and Cat 5 cabling, I had to turn the 'Upper Baseboard' into a 'Mezzanine Baseboard'. This board carries all the more active stuff, eg the two Pis, the Stereo Bonnets and the two MOSFET Driver Boards. I added a pair of barrel connectors so that the Mezzanine can be removed for access with no de-soldering necessary. A small Veroboard allows the Pi3 and the Fans to be powered at the same time. This gives the benefit that the fan current does not go through the Pi.

The 'Lower Baseboard' carries the two DC-DC Converters and the networking components, so should rarely need accessing once the system is fully integrated.

The system seems to run pretty cool and consume very few resources. The following printout shows the data after the system had been playing for around 20-30 minutes:

CPU Usage (%): 2.3
Memory Used (MB): 48
CPU Temperature (Deg C): 35.4

This was pretty constant all the time the music was being played with the rising only about 2 degrees. I think our biggest problem, temperature wise is going to be heat being imported into the equipment case from the Nave rather than heat being generated inside the case. The Pi Zero is likely to generate a negligible amount of heat.

Once I've completed the wiring and enough software development to be representative, I'll see if I can monitor the ambient temperature inside the case with the lid on.