Curiosity Question about 'touch16' command

[IronJungle]

Simple program is:

main:
touch16 C.1,w0 ' this is a "wire" connected to nothing
toggle b.7 ' flash LED
pause 100
goto main

I'm just playing with the command and noticed that when I touch the "touch sensor" wire the LED will blink much much slower that when it is not being touched.
- Why is that? Does the PICAXE detect a change in the touch input oscillation and have to sample several cycles to determine the new value?

Also, the manual 2 says "Never directly touch’ a touch sensor (e.g. a piece of bare wire)!"
- Why? Possible damage to the PICAXE? Or an attempt to control the capacitance the touch sensor will see? Safety to the user (doughtful)?

No project at stake. Just my quest for knowledge.

Thanks.

 

[nick12ab]

I'm just playing with the command and noticed that when I touch the "touch sensor" wire the LED will blink much much slower that when it is not being touched.
- Why is that? Does the PICAXE detect a change in the touch input oscillation and have to sample several cycles to determine the new value?

Something to do with the proximity of the finger affecting the capacitance of the touch sensor then the PIC charging and discharging this 'capacitor' and seeing how long it takes. Please read this and this.

Also, the manual 2 says "Never directly touch’ a touch sensor (e.g. a piece of bare wire)!"
- Why? Possible damage to the PICAXE? Or an attempt to control the capacitance the touch sensor will see? Safety to the user (doughtful)?

I couldn't find any info on this, but maybe static electricity on the person could damage the PIC?

 

[IronJungle]

Thanks, nick. Good links. Curiosity calmed for now.

 

[boriz]

Never tried touch interface, but this from the online command reference could be the answer:

"In simple terms a touch sensor works by detecting the change in capacitance when a finger is placed near the touch sensor pad. This capacitance affects the frequency of an internal oscillating signal. By measuring the time it takes for a set number of oscillations, the relative capacitance can be calculated. This value will change when the finger is placed nearby - the finger increases the total capacitance which then decreases the oscillation speed, and so the time taken (value) of the touch16 command increases."

 

[boriz]

On the same subject. It says not to connect any other external components to the sensor wire/pad. I'm wondering if a piezo 'sounder' disc could be made to do double duty. Make beeps and be a touch pad. Hmmm...