# water as touch surface

project aims at using water surface can be used as touch pad
construction - a cubical bowl of tap water , 2 sheet electrodes for 1 pair (y-axis pair)of opposite face(square wave 10Hz 10v Vpp), 2 sheet electrodes for the other pair (x-axis pair)(similar square wave lags by half cycle )
left hand touches adc pin. right hand touches water surface.10v drops linearly with normal distance from pulse electrode
process adc input for realtime x-y coordinates of touch (maybe z also if added 3rd pair electrodes at surface and floor)
so water surface can be used as touch pad .
any thoughts on how the algorithm would look like?

An interesting idea

Display the values, measured while a pulse is applied, to find out more.

It may help if you increase the conductivity of the water...
Also keep in mind the depth of immersion will vary the levels slightly.
Interesting.

lastchancename:
It may help if you increase the conductivity of the water...

adding salt to water will cause electrolysis , so it disrupts uniform composition of water.
voltage drop will not vary linearly with normal distance from pulse electrode

SumitAich:
adding salt to water will cause electrolysis , so it disrupts uniform composition of water.
voltage drop will not vary linearly with normal distance from pulse electrode

You're right - but I was making a point about conductivity - not specifically adding salts.

body is picking up lots of interference and electrostatic discharge that get into the ADC.

Essentially you get two different voltage levels, one for each direction of the signal polarity. Since you know when the voltage is applied in either direction, you can measure the voltage for only one direction.

SumitAich:
body is picking up lots of interference and electrostatic discharge that get into the ADC.

the ADC really wants ~10k as the source impedance. So the water impedance is ~ ten times too high for reliable ADC measurements. A buffer amplifier seems necessary.

There are similar 2D positioning systems that inject signal current or noise into a point on a resistive sheet. The edges of the sheet are tied to virtual earth with op-amps that convert each edge current to a voltage. Those four voltages are a function of the sheet x–y position where the current is being injected.

I remember this project, 2000 years ago, Jesus did it, but he never shared the code..
people sometimes are selfish

Domino60:
I remember this project, 2000 years ago, Jesus did it, but he never shared the code..
people sometimes are selfish

how do i solve adc source impedance issue?
the ADC really wants ~10k as the source impedance. So the water impedance is ~ ten times too high for reliable ADC measurements. A buffer amplifier seems necessary.

body is picking up lots of interference and electrostatic discharge that get into the ADC.
how do i solve adc source impedance issue?

the ADC really wants ~10k as the source impedance. So the water impedance is ~ ten times too high for reliable ADC measurements. A buffer amplifier seems necessary.

Yes an op-amp buffer/filter could resolve above issues.

The guy on the left is the one that copied his code off the internet.

"Why am I sinking? This worked great on land! Fix this for me now!"

-jim lee

jimLee:

The guy on the left is the one that copied his code off the internet.

"Why am I sinking? This worked great on land! Fix this for me now!"

-jim lee