How could I earth my cat?!

My Robocat is planned to purr when petting.

Petting means humans touching his "fur" = capacitive touch sensor => purr (loudspeaker + EEPROMs).

The touch capacitive sensor is this one:

Command is via Arduino Uno. For the time being, the Arduino board is connected to a Desktop PC, to transfer the code. To feed all sensors and memories, there is a separate power source.

According to the reference section in this web-site, the capacitive sensor shall be connected to earth somehow in order to properly work.

The cat is going to be on batteries alone when the project will be completed.

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Question is:

For practical reasons, is there any other possibility to "earth" the Robocat, besides sticking a wire connected to the water supply network in his mouth?

Thank you!

falexandru:
Question is:

For practical reasons, is there any other possibility to "earth" the Robocat, besides sticking a wire connected to the water supply network in his mouth?

No.

How does work then the electronic equipment on International Space Station?

This is a serious question.

The space station is its own ground.

For the capacitive sensor its sensing the impedance between its sensor pad and its ground wire - normally
that would be a capacitance to a resistance (human body) to a capacitance to ground of the human.

You'll probably find that just having a long wire as ground connection on the cap sensor will do the job -
basically any large enough conductor is going to have significant capacitance to ground or the human.

For a ground-free capacitive sensor you'd have parts of the sensor running in antiphase, using the hand as
a capacitively coupled resistor between the parts of the sensor.

MarkT:
For a ground-free capacitive sensor you'd have parts of the sensor running in antiphase, using the hand as
a capacitively coupled resistor between the parts of the sensor.

I dont get it :frowning:

falexandru:
Question is:

For practical reasons, is there any other possibility to "earth" the Robocat, besides sticking a wire connected to the water supply network in his mouth?

Thank you!

A mobile phone's capacitive screen isn't earthed.

How could I earth my cat?!

When it dies put it in the ground.

.

larryd:
When it dies put it in the ground.

.

Next to you. :slight_smile:

sensor 'ground' to system supply negative (B-)

You are not grounded. The capacitive sensor measures capacitance between the sensor plate and it's circuit common. When you move your hand near it, there is parasitic capacitance between you and the sensor plate, and you and the circuit common. These capacitances are in series and so are quite low.

Connecting circuit common to earth ground makes the parasitic capacitance between you and circuit common larger.

Without grounding your "cat", try increasing the area of circuit common by attaching the metal chassis to circuit common. You might even try placing two areas of metal on either side of the capacitive sensing plate. Something like this:

@polymorph

I shall look deep into your post. Thank you!

Southpark:
A mobile phone's capacitive screen isn't earthed.

What about when the phone is connected to a charger?

The phone’s capacitive screen uses a grid of transparent conductive lines. It scans them and detects an increase in capacitance from one line to another, not to ground.

So charger or not, it makes no difference.

For a touch switch, such as using Arduino’s capsense, it is measuring between the touch terminal and circuit common. In that case, using a plug-in power supply will increase sensitivity as there is capacitance between the primary and secondary side of the power supply, even if the output is isolated and ungrounded.

AWOL:
What about when the phone is connected to a charger?

Good question. Depends on what it is charging from. If USB at a PC (computer) .... then maybe yeah. But if using a typical two pin wall wart charger.... not earthed.

As I pointed out, it does not have to be directly connected to Earth. It only has to have more capacitance between circuit common and Earth or just surrounding conducting structures. Like the wiring in the wall, a metal table, etc.

When I build handheld battery powered devices using capacitive switches, I always put a shield inside the case, if the case is plastic. This increases the parasitic capacitance to the hand holding the device.

polymorph:
Without grounding your “cat”, try increasing the area of circuit common by attaching the metal chassis

Nice pics!! When the finger goes near the button… are the capacitances kind of like this?..

touchcap.jpg

Yes, except you duplicated the caps that are already there, in the green areas.

aarg:
Yes, except you duplicated the caps that are already there, in the green areas.

Oh yeah....true. Thanks aarg.

falexandru:
How does work then the electronic equipment on International Space Station?

They ground controls to Major Tom.

aarg:
They ground controls to Major Tom.

And today’s Winner Of The Internet prize goes to … aarg.