Board Mounting

[sentry7]

Hey Guys,

I'm working on a small project and require some guidance managing the hardware aspect (screws, mounting, holes).

This is supposed to be a simple wall clock. The clock has front and back rectangular panels made of acrylic. The electronics are to be housed between the two panels.

The front panel has numbers cut out and LEDs are supposed shine through the cutouts.

Below is an attempt at a technical drawing of what I had in mind. A and B are the acrylic front and back panels respectively, and C is the PCB. Panel D holds the LEDs which are mounted. E is the clock battery holder.

My design questions come in when I consider bringing all of these panels together; how can I join them, but also space them to my liking? Also, how could I electrically connect the LEDs to the PCB (simple wires to holes in the board, perhaps?)

[dom0]

Wire the LED matrix directly on the LED panel and connect only row/columns.

As for mounting:

M3 distance bolts ; numerous sizes are usually stocked by every electronics shop.

[tautech]

dom0's solution is usually the neatest, however threaded rod and 2 nuts per layer will also work well.
Just depends on how neat you want the job and what you can easily source locally. 

[SeanB]

For spacers just cut some acrylic rod or sheet to the required spacing and use acrylic cement ( which is not the same as glue, but is acrylic dissolved in MEK or a 2 part MEK loaded epoxy) to join the spacers to the front and rear panel. LED board is held in a notch cut in the spacer and the main board the same. Take thin sheets and make a battery holder to hold the battery pack, welded to the back panel.

[rdl]

What dom0 suggested.

You will probably find these listed as "stand offs" at most places in the US, such as Mouser, DigiKey, etc. They come in a huge variety of types and sizes. They are just about the only way I mount pc boards.

http://www.mouser.com/Electromechanical/Hardware/Standoffs-Spacers/_/N-aictfZscv7?Keyword=stand+off&FS=True

[zapta]

Why not having the leds soldered directly to the PCB?

The mount and spacing is pretty easy. Have one threaded standoff (female on both sides) in one space (e.g. between B and C), then non threaded spacers in the other spaces (AD, and DC), then have on both sides screws that goes through the acrylic all the way to the threaded standoff.

Search for example at Sick Of Baige.

I did something similar here with 3mm screws. BOM at the bottom here https://github.com/zapta/power-monitors/blob/master/pmon_3v8/eagle/pmon_3v8_bom.csv  , and this is how it looks form the front




McMaster and Digikey should have the screws, spacers and standoffs you need.

[sentry7]

Why not having the leds soldered directly to the PCB?

That was my first plan, but the board would have to be as large as the front panel for the LEDs to be placed where they're supposed to be with respect to the front panel. Having a separate LED panel would minimize cost; the board house I'm using charges based on the area of the board.

[Ian.M]

So you are hand-wiring your LEDs?  Ribbon cable to a single plug on a header on the PCB is your best option there, but make sure its accessible to disconnect for board removal, is secured to the LED panel and has enough slack to permit the PCB and LED panel to be run opened out side by side for bench testing.

Assuming front panel appearance is important, I'd use threaded insets in acrylic bosses glued to the back of the front panel, and hollow acrylic spacers glued to both sides of the LED panel and to the inside of the back panel, with long machine screws from the back holding it all together.

[jona0497]

I used 2.5M threaded spacers in a similar setup. One spacer female/female and one spacer female/male. This worked quite well and these types are generally available in many lengths, so you will probably find something in the length you need. Don't forget the thickness of the acrylic when choosing your screws 

[tautech]

Welcome to the forum.

Nice project, very tidy. 
Care to share it's build in a thread as a project for others?