Help with a touch switch PCB’s that don’t work right…

Hi everyone...

First, I'm not an electrical engineer, I'm a model builder, replica prop maker and hobbyist mechanical engineer, so please excuse my ignorance in EE and possibly simple problem...

Problem:

I recently designed a touch switch based on a 555 timer chip that I wanted to use to light up a model airplane based off of a TV show... Marvel's Agents of SHIELD. It worked right from the start... from breadboard to the pcb I made, worked without issue.

There was enough interest in the switch that I decided to make more of them as stand-alone, battery operated (9v) units... and this is where my issues started. The main issue with it all was it wasn't shutting off.

The circuit for the switch works on the breadboard, but when I made the PCB's based off the first one (with appropriate modification to account for the battery operation and fewer LED's), it wouldn't shut off... After much searching, I found that the circuit was becoming very sensitive due to the addition of the aluminum parts of the emblem and found that a 10nf cap placed between the aluminum "trigger pads" (pin #2 on the 555) and ground (pin #1) solved this.

I redesigned the circuit board, etched out new pcb's and started to assemble them thinking all is well. It wasn't. None of the new circuit boards worked correctly. Same issue came back as before where the unit wouldn't shut off. I've been at this for months now and don't know what could be the cause. The only thing left is the PCB's themselves are faulty. Either the traces are too thin (0.4mm) or there's a flaw in my design somewhere else, possibly some design rule I'm clueless to that I'm overlooking.

Can anyone please help? I can send a schematic and even a pdf of the design of the PCB's.
Any help at all would be greatly appreciated.

Thanks in advance.
Ted

Hi Ted,

It would be greatly appreciated if you can attach the schematic of your design.

Thanks,
Kevin

Hi Kevin,

Thanks for your response... as requested, here's the schematic of the setup.

There are 2 versions of the PCB's... one for SHIELD and one for HYDRA.

Differences are as follows...
- SHIELD pcb is broken up into 6 pieces and use 15 white LED's (5mA each) where as the HYDRA version uses a single round PCB and 14 red LED's (20mA each).

- SHIELD version has more of the 4mm aluminum as trigger pads because of it's design.

As I mentioned before, on the breadboard all this works without issue even when I connect the Aluminum SHIELD or HYDRA trigger pads (which are bonded to frosted acrylic).

Hi Theo,

From what I am seeing, First I can't find your ground. You need to consider the digital and analog ground. The digital ground will provide a certain voltage reference compare to analog ground that is usually zero. Second, maybe your 555 timer is not working properly. The 555 timer releases a pulse that provides the interrupt.

I also tried searching the web for similar circuits, I think its the same with this one: "Touch Switch("")":http://www.555-timer-circuits.com/touch-switch.html and "555 timer("")":http://www.electroschematics.com/8435/on-off-touch-switch-with-555/

If the problem is just how to turn it off maybe you should modify it having the off/reset button manually.

Regards,
Kevin

Thanks for all your help Kevin... I appreciate it.

I figured out the issue, made a new PCB and it worked flawlessly.

Thanks again.