Teensy3.2 pin input prootection

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Teenfor3

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Just wondering is there any recomended way to physically wire teensy3.2 analogue or touch pins to sensor pads and plates, so as to give protection to the board from short circuits or other static voltages etc. ...... so as not to alter the sensitivity of sensing too much. My project is not using actual measurement values accurately, just need to know the changes that take place so to know a pad is touched by something and teensy senses it. I have used 220 ohm resistors in series with the pins, in my mind to avoid short circuits between pins due to say cut wiring etc. Just wondering is this necessary or what other recommendations
 
See the ruggeduino schematics for an exhaustive discussion and description.

For example, they use a 0603 Polyfuse as a input resistor plus a zener or TVS.
 
One problem with an input Zener or TVS is that it often adds > 10 pF of capacitance, and thus will significantly change the capacitive sense values of the pins.
If you can live with that, using such protection is highly recommended!
 
Thanks for the good information, The ruggeduino seems to be well protected but is it needed for normal situations?.
The additional capacitance may not be a problem....I would have to try it and measure the results. I just use the touchread to take a reading and if it below or above a mid value let it switch something. I currently get reading about 1000 when pad not touched and 6000 upwards when touched. I test for values about 3000 and use that to switch. So I assume the readings would just go up a bit, there would still be a difference when touched or not touched.
But I think my original question.....Is it necessary for ordinary domestic use?......Do most people fit them in their projects??......Does my 220 ohm resistor in series really give any protection on its own?......
 
I haven't bothered with input protection for the touchSense pins for prototyping but I haven't put a huge number of hours on my gadgets, I don't live in a particularly dry area and don't have wall-to-wall carpeting. My excuse is that I'm trying to get a feel for how fragile the parts I'm working with are. I'm surprised at how few things I've 'smoked' in the years I've been tinkering. I haven't seen any mysterious failures that could be ESD.

One easy thing you can do is add an insulator over the touch pads. A coat of varnish or tape ought to provide modest short circuit or ESD protection. In future builds, I'll do this and add a resistor. If I was really worried about reliable input sensing--say for a museum exhibit or for something particularly difficult to service, I'd buy a rugged push button or buy a sensor designed for harsh environments.

ESD damage is cumulative, usually undetectable at the time and unpredictable regarding exactly what gets damaged. In a factory environment or lab that deals with sensitive components, ESD usually taken very serious: grounded and static dissipative work surfaces, humidity control, static-safe instruments, static dissipative lab coats, shoes, floor mats, etc.
 
Is it necessary for ordinary domestic use?

If this is something your family will use, and/or that will cause inconvenience if it fails, and/or that needs to run for months or even years once completed, then yes!

A resistor is fine -- it does add some protection. If you couple it with a Zener, you're doing very well. Then your next problem will be robust power supply :)
 
I actually had the same question as the OP. I haven't tried anything with the Teensy 3.2 yet (too many things already on my plate), but I'd be curious if anyone has a solution that would do a good job protecting a commercial product built around the Teensy.

I normally use a pair of Schottky diodes (fast and .3v drop) in addition to a 1k - 10K resistor for protecting analog and digital inputs on several PIC microprocessor projects with good success. I just don't know if these will work with capacitive sensing inputs. Anyone care to test and report back?
 
Anything connected to the Touch pins will make a change to the touch reading. Even component layout, long cables or multicore cables. Initially I was only concerned about protection for shorting pins together or to ground so I only use a series resistor to limit any current ???. I was only wanting a switch point when touched so just reset to suit. If you are actually measuring capacitance you would need to recalibrate and ensure the layout and connections are stable.
Regards transient suppression you will need diodes or TVS suppressors, capacitance is usually listed and fairly low. I considered this but due to the need for every pin to be suppressed etc thought it wasnt worth it for normal use. The problem is it will be needed for commercial use CE marking etc. Every exposed pin connection will be zapped with at least 8 kV and subject to work within a 15 kV electric field. The testing for this costing several £1000s. So I gave up I would need to be selling hundreds of the devices to even recover the costs of testing and any changes or mods I make would need re-testing. I was wondering has anyone CE tested a device using Teensy with exposed pins connections or Touch pads connected. OR can Teensy be used as a component in a "bigger" commercially sold device.
 
I was wondering has anyone CE tested a device using Teensy with exposed pins connections or Touch pads connected. OR can Teensy be used as a component in a "bigger" commercially sold device.

My experience probably not relevant because my widget has no directly "exposed pins". Would suspect that the MM would be relevant for direct Teensy contact, and the HBM data would be applicable for the end-use box that implements the Teensy module. That said, an IC's MM model data is not useful because your design should not expose our precious Teensy to this cold, cruel, and unforgiving world.

Just finished a regression series that included the IEC61000-x-y immunity stuff for a box with a T3.2 installed because of a design change. The -4-2 test levels were 8kV/15kV (contact/air) indicated no problems - accomplished mostly by controlling current, but do use TVS diodes for some I/O lines. The susceptibility paths were the keypad, a switch, and the various I/O connectors, where degraded operational modes were detected after 147 EOS events in the keypad or 12 events on a second (unused) current sensor connector. Well duh, none one has ever used more than one current sensor in the field, so it is gone.

The -4-4 and -4-5 tests had unexpected results. Although no margin decrease from previous design for my box, it did break some stuff in the customer's box. Once you get past 600V to 1kV, propagation paths can get interesting. Mechanical design and layout is important for this stuff.
 
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