Switches-on-PCB problem

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Early in this (multi-unit) project I had intended to mount tactile switches directly on the PCB and then mount the PCB up against the front panel. This would have allowed switch holes in the front panel that was going to use an overlay. Problem is this: the circuit now needs an Omron relay that makes tactile switches not possible because of the above-board height of the relay. Grrrr.

This project only needs 3 momentary switches and I'd like to avoid manually drilling holes in the panel and manually wiring the switches. I've looked for a standard (no NRE) 3-switch membrane switch assembly but have come up empty so far.

Any suggestions would be appreciated before the PCB design starts.

Chris

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Could you not mount the relay on the backside? Or is it surface mount?

Maybe a picture of the board layout might help...

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hugoboss wrote:
Could you not mount the relay on the backside? Or is it surface mount?

Maybe a picture of the board layout might help...


Actually that's a great idea. There will be plenty of space underneath the PCB. The PCB has not yet been designed so I still have flexibility on component placement.

I'm also aware I could make a switch daughter board but the relay underneath should work. The Omron G5LE dsheet doesn't show any relay orientation limitations.

Chris

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Normally if you make a 2-sided board, only your "human interface" components should be on the "front" of the board, like LCD, keypad, buttons. Put everything else on the back side. This is useful too for servicing, you just remove the casing's back panel and have access to almost everything.

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...and there are tactile switches available with long actuators.

Ross McKenzie ValuSoft Melbourne Australia

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Hugoboss, good point on servicing too. Glad I asked before I started the PCB design.

Ross, I looked at Omron, E-switch, and a few others but didn't see any actuators long enough. I'll look again.

Chris

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Ross McKenzie ValuSoft Melbourne Australia

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Ross, has Rueben the Wurth rep been to see you?

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No.

Ross McKenzie ValuSoft Melbourne Australia

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Maybe some other ideas :
* Extend the switches (glue some self-made part on it)
* Put all switches and leds on a seperate board. If sales is going well, you can easily take the next step and order a custom frontplate with integrated switches and leds.

example :
http://www.polychromal.nl/en/int...

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hugoboss wrote:
Normally if you make a 2-sided board, only your "human interface" components should be on the "front" of the board, like LCD, keypad, buttons. Put everything else on the back side.

...unless size is a concern, or unless you need to put 400-500 decoupling capacitors under your FPGA. :shock:

I've done many designs where size was the driving priority. As long as you take care to make sure the board can be assembled w/ two passes through the reflow oven, there should be no reason not to pack components on both sides.

Science is not consensus. Science is numbers.

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Ross, thanks for the switch example. 13mm actuators would be more than long enough.

Paddy, I also had the daughter board idea but it's not my first choice for lots of reasons.

Hobbss, luckily for this product size is not a major issue. So the 2x16 lcd and the 3 switches would be the only things on the front panel side.

If I could squeeze another question out about the switches: how far do you guys usually have the switch actuators extend above the front panel when they are sitting behind an overlay? I would guess the pre-travel spec + ~.1mm.

Thanks.

Chris

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If you use low-profile displays you can get away with switches with quite a short shaft.

I've just received these boards back for a customer's project. These use a 7mm total height switch with a 1.2mm front panel. The only components on the 'top' are the switches and the display with everything else being on the back.

These are being using with a custom hot-embossed overlay keypad.

I've yet to finalise the protrusion of the switch as I'm waiting on my customer to send me the metalwork but it's looking like it'll be around 0.2mm.

The display is a 2x16 device with white LED backlight and an I2C interface. I buy them in the UK but there is something very similar in Newhaven's range.

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Pulsar ProFX, Flexible PCB has some pictures and photos on use of a thin substrate for thin keyboards (membrane switches or dome switches).

"Dare to be naïve." - Buckminster Fuller

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Brian, awesome info and pictures, thanks for taking the time to post them. Very helpful.

I did check Newhaven's line and found one (NHD-0216T2Z-FSY-YBW-P, http://www.newhavendisplay.com/nhd0216t2zfsyybwp-p-4162.html that is 2mm shorter but neither Digikey or Mouser stock it. Might be safer to use a standard 8.6mm height unit and slightly longer switches.

It looks like you are soldering your LCD directly to the PCB. If I could just use a 1x16 header and solder to LCD and PCB that would make assembly so much easier. Wondering how reliable these LCDs are.

Thanks again.