Tired of manual switches? Simple Touch switch pass thru for under $15.00

[Java_Az]

Went dyslexic there but yeah your right N channel should be used to switch a ground i am always confusing that with gate polarity.

I dont think you will have trouble with the gate it is rated @ 26nC to open it. Didnt know what a Coulomb was till today so at least i learned me something.

The coulomb (symbol: C) is the SI derived unit of electric charge, transported by a steady current of one ampere in one second. 1C=1A x 1s

A nano Coulomb or nC is 1 / 1,000,000,000 of a coulomb The only thing i can figure after all that, is it cant take much juice to open a gate.

 

[Scubabatdan]

Went dyslexic there but yeah your right N channel should be used to switch a ground i am always confusing that with gate polarity.

I dont think you will have trouble with the gate it is rated @ 26nC to open it. Didnt know what a Coulomb was till today so at least i learned me something.

The coulomb (symbol: C) is the SI derived unit of electric charge, transported by a steady current of one ampere in one second. 1C=1A x 1s

A nano Coulomb or nC is 1 / 1,000,000,000 of a coulomb The only thing i can figure after all that, is it cant take much juice to open a gate.

Close the gate yes, 1, 2, 5 ... 3 sir... 3!
LOL
I love Monty Python...
Don't worry we are all LyxDexic once in a while
Dan

 

[Scubabatdan]

How does this look?
Dan

Added:

Just ordered these from DigiKey:
10 AT42QT1010-TSHRCT-ND-----IC TOUCH SENSOR 1KEY SOT23-6
10 RHC2512FT1K00CT-ND--------RES 1.0K OHM 2W 1% 2512 SMD
10 709-1207-1-ND CAP X2Y-------CER 2.2NF 100V X7R 0603
10 445-5446-1-ND CAP CER-------5.0PF 16V C0G 01005
10 P4.7MECT-ND RESISTOR-------4.7M OHM 1/4W 5% 1206

And yes... there all SMD LOL... we will see how it goes....
Dan

 

[slopes]

Looks great Dan - I shall stay tuned in.

 

[Java_Az]

0603 is the smallest i will hand solder i got some 0402 by mistake once and they are like trying to solder a fleas .... onto to a board. I think you might have trouble with the 01005 it is tiny i mean really tiny. Over twice as small as a 0402. Here are the measurements from the data sheet

 

[Scubabatdan]

0603 is the smallest i will hand solder i got some 0402 by mistake once and they are like trying to solder a fleas .... onto to a board. I think you might have trouble with the 01005 it is tiny i mean really tiny. Over twice as small as a 0402. Here are the measurements from the data sheet

Well that is what jewlers glasses are for Well I bought em I guess I will try and solder them... Could be a futile effort, but lockable tweezers help. I will look for a larger footprint in the mean time.
Dan

Well these look better:
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=490-3558-1-ND

 

[Scubabatdan]

OK so I did some research and actually learned somthing! LOL

Attached are the SMD size comparision and their physical 2D dimensions excluding height. Yeah your right 0420 is really small!
Hope this helps someone using ExpressPCB, I know it has helped me with designing the pads for the chips!
Dan


Added:
I redid the PCB circuit for SMD's and set the pads for the appropriate sizes.

Just waiting for the chips, will make the PCB tonight.
Dan

 

[Java_Az]

Glad i could help , I am by far no electronics expert just trying to give you the benefit of all the mistakes i made in the last 5 months. It sucks to get your digikey or mouser order to find out you ordered something unsolderable by a human, then having to wait another week to get more usable parts. I went threw my box of parts i never should have bought and i was wrong i ordered some 0201's. Still dont think i would mess with 0420's though.

let us know how this goes. I am thinking about maybe making a digikey order and trying this out. But i think i will see how your project goes first.

 

[Scubabatdan]

I will give update as I progress. You know if this works, (Big Grin), I could make a clip on mouth piece sensor. This would bypass the need to touch or push anything. The lips electric field would be picked up by the ATQT1010 chip energizing the MOSFET switch turning on the atty. A small clip with a piece of mesh glued to the inside and two wires running back to the PV would be an easy setup, no electrodes to touch just plastic. This would be awesome if it works.
Dan

 

[slopes]

Dan - I note you haven't included a master on/off switch on your diagram. I'd have thought it important to have one on this set-up.

 

[Scubabatdan]

Most on off switches are extenal to the chip (built into the box). I am only working on the chip at this point to see if it is a viable project to refine and pass along to the masses.

But yes every mod should have an on off switch, unless it is a PT. But even then I would recommend a PT be disconnected when not in use.
Dan

 

[Java_Az]

Just started my own layout. You might want to check the footprint for the AT42QT1010. Seems like it is a bit big on your layout. Data sheet shows it as a SOT-23-6 which it smaller then a SO-8 (mosfet). Maybe it is just optical but doesn't look right on this screen.

 

[Scubabatdan]

Roger, I remade that foot print this afternoon by the sheets specs. Since it is on the "Work" computer youll have to wait until tommorrow before I can upload it. I can upload the .pcb file if you want a ready made layout to play with. Let me know...
Oh here is my first failed attempt, the iron was not hot enough... And I only printed out one copy, I will have more printed out tommorrow.



Does the QT1010 footprint look better here?

Dan

 

[Java_Az]

The express PCB file wont work in Geda which is what i use. I run linux for a OS. But i guess i could install a windows Virtual machine to get it to work.But I am almost done with the layout so i wouldnt worry about it. Maybe other folks who run windows might want access to it.

 

[Scubabatdan]

The express PCB file wont work in Geda which is what i use. I run linux for a OS. But i guess i could install a windows Virtual machine to get it to work.But I am almost done with the layout so i wouldnt worry about it. Maybe other folks who run windows might want access to it.

Well here are a couple files that may help everyone, I reversed the image and printed it out and everything looks like it matches up good. I will post the .pcb file for the windows users, a powerpoint file that is full of the circuit image reversed and a .jpg of the circuit reversed. these are all ready for printing on a laser printer and then to transfer onto you copper PCB.
Ok had to make links to the pcb and ppt files, just download em from my filesanywhere account.
ExpressPCB .pcb file
PowerPoint .ppt file
Dan

 

[Scubabatdan]

Well the prototype board is done, just need the rest of the chips! LOL
Here she is...


Dan

 

[Scubabatdan]

YEAH! the chips will be here tomorrow!
UPS Scheduled Delivery:
Friday, 04/22/2011, By End of Day

Should have a test ready for Saturday!
Dan

 

[Scubabatdan]

Ok got my chips in yesterday, here is the PCB with everything attached

And here is a youtube video showing operation. Unfortunantly I will have to lower the value of the field resistor from 1k down to 100ohms. But for a VERY sensitive touch switch it does work, now to fine tune it!
Dan

 

[Java_Az]

Nice job glad to see it working. 100ohm should make a lot more sensitive. I guess i have a digikey order to make here really soon. let us know how the new resistance works out.

 

[Scubabatdan]

Ok the sensitivity, after reading the chip specs for the 100th time indicates that the sensitivity goes up as you increase the Cs value. "For a 3v input the Cs value should increase to 8.2nf" So for a 3.7v input the Cs value should be 10nf. So I am ordering the following chips:
10nf
27nf
47nf
I also read a note:
For proper operation a 100nf (0.1uf) ceramic bypass capacitor must be used directly between Vdd and Vss, to prevent latch-up if there are substantial Vdd transients.
So I guess I wil order a 100nf capacitor also and place it between pin 2 and 5 with the proximity closes to pin 5.

More testing once I get the chips...
Dan