• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

qt100 capacitive touch IC

Status
Not open for further replies.

strokedmaro

New Member
I'm having difficulties getting this IC to work on my breadboard. I think its partially due to the fact that I don't fully understand the datasheet. This is a single channel (1 button) IC but the datasheet does not show what value to use for "RE" and I'm not sure if "Cx" is an actual cap or not. It also does not accurately describe how the electrode is made. Ive seen other electrode designs and they are almost always 2 contacts (like a circle inside another circle physically seperated with a gap between them) but the data sheet shows it more like a single electrode.

Anyway, I have it setup like figure 1-1 in the datasheet using cap's of the valve suggested in the paragraph below the diagram. (10nF and 10pF) "CX" is grounded as pictured and the electrode is basically a strip of 5 breadboard inputs. What I find odd is im using an led on pin 2 to show when the switch is made and it is constantly on. When I put my finger over the "electrode", nothing happens...it remains on. (This I'm sure is due to the tiny surface area of my current breadboard electrode) However, when I touch the leads of either resistor the LED goes out and comes back on about 3-4 seconds after I remove my finger. I would have thought that the LED would be out as long as I did not activate the switch. It works like a normally closed switch at the moment and requires me to physically touch it like a resistive touch IC.

Im using 470k resistors for Rs and Re, caps as described earlier and a V reg. putting out 4.5 vdc. Any help appreciated!!

DATASHEET: http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=427-1091-ND
 
Last edited:

KMoffett

Well-Known Member
Cx is the virtual capacitor formed by your hand "approaching" the sensor electrode. I've used a 2" square of foil (on the inside of a glass display window) attached to a 15" wire attached to Rs of 10KΩ, no Re, and 0.01µF for Cs. Attached is the schematic. The SW1 selects whether the output of the 555 is toggled or timed by the output of the QProx chip.

Ken
 

Attachments

strokedmaro

New Member
KMoffett said:
Cx is the virtual capacitor formed by your hand "approaching" the sensor electrode. I've used a 2" square of foil (on the inside of a glass display window) attached to a 15" wire attached to Rs of 10KΩ, no Re, and 0.01µF for Cs. Attached is the schematic. The SW1 selects whether the output of the 555 is toggled or timed by the output of the QProx chip.

Ken
THANKS!!! couple of quick questions. I should be able to substitute a voltage regulator for the transformer in your schematic correct? What is the value for R6 and what is the range of R3? I can't find 1m10t anywhere...substitue? Also, is it normal operation for the qt110 to be normally on as I described in the first post? THANKS AGAIN!!!
 
Last edited:

KMoffett

Well-Known Member
A 5v regulator would be fine. The transformer/rectifier/capacitor were part of a larger circuit. Because of the low currents involved I went with the resistor/zener for this part. The output is Active LOW...see Section 2.2 and Table 2-1 in the datasheet.

Nigel,
I did all my testing on a bread board. It has a built it self-calibration feature at power-up, so it sort of adjusts itself to it's ambient environment. They give some caveats about ground planes on a PCB though.

Ken
 

strokedmaro

New Member
Next problem ;) Got it to work a few weeks ago and its amazing. The only problem I have now is that this will be used in a car to control a relay and it defaults "On" when power is removed and reapplied. Is there any way to keep it off when power is applied? If not, I may have to go another direction. THANKS. BTW datasheet is attached to the first post
 

crutschow

Well-Known Member
Most Helpful Member
strokedmaro said:
Next problem ;) Got it to work a few weeks ago and its amazing. The only problem I have now is that this will be used in a car to control a relay and it defaults "On" when power is removed and reapplied. Is there any way to keep it off when power is applied? If not, I may have to go another direction. THANKS. BTW datasheet is attached to the first post
Which mode are you using: DC Mode or Toggle Mode?

You could use a transistor at the output to invert the output polarity.
 
Status
Not open for further replies.

Latest threads

EE World Online Articles

Loading
Top