5V Touch Switch Mod ??? Unsuccessful this time :(

Experimented with using an NE555 chip as a touch switch. Started with this schematic:



Removed the LED from pin 3 and used this output to operate the control pin on the 4-pin MV 3A VR. By substituting components, I got it working great on a breadboard. I wish I had drawn schems as I went Somehow I screwed up when moving components to a PCB, cause now it's firing ALL THE TIME, darn!

I know the VR takes a neg signal to trigger it, somehow I was able to use pin 3's low state to trigger the VR control pin. Man, wish I could remember how I did that

Back to my breadboard today. I will solve this problem (some day). I already have my 3AA clear box all drilled and rewired and have a pair of brass rivits mounted as touch points, so it's too late to turn back now ...

View of front of mod. You can see the my mini-leds on a pcb (bottom right). Also see brass contacts .. 1 to ground, 1 to pin 3


Already started stripping components from board

By asnider123 at 2011-03-27

 

Where do find places that sell Mega ohm resistors? Those are hard to find in the US and cost quite a lot for something usually cheap. I know a touch sensor requires resistors somewhere in the 25-50M ohm area. Radio shack has the 10ohm ones but I would prefer using just one and not five. I have a touch sensor kit also, the required 5 resistors but would like to use just a single one. If you know of any places in the US with decent prices and don't have to buy a minimum of 100, please let me know.

Aloha, Keith

 

Keith, if you dont mind waiting for the slow boat, you can get them for 1.8 cents apiece from

NEW 100 X Resistors 10M Ohms 1/4W 1% Carbon Film Free - eBay (item 220582731079 end time Apr-26-11 20:05:38 PDT)

Or order your choice of 100 resistors (any value) 1/4 watt for 3 bucks
http://cgi.ebay.com/NEW-100-X-1-4W-...442?pt=LH_DefaultDomain_0&hash=item4cf624a612

Or 100 your choice 1 watt for 3 bucks
http://cgi.ebay.com/NEW-100-X-Resis...092?pt=LH_DefaultDomain_0&hash=item4cf34300c4

I just cant decide

Think I will order, in no rush

 

Keep it up man, I have no doubt that you will nail this one soon

 

Yabetcha, might take a bit, want to order a resistor assortment, thanks fella

 

Asnider, I need a single 50mega ohm resistor or at the very minimum, 2 25mega ohm ones. The 10mega ohms ones can be used but I would prefer not to use 5 resistors. If you can find any 25mega or 50mega ohms resistors, please let me know.

Aloha, Keith

 

Is there a reason why you took this rather complicated approach.

Using a mosfet seems a bit easier.

This design, from a decade ago works well for firing a regulator.

​

For our use we just need a more appropriate N-mosfet. The main concern being Gate Threshold Voltage should be ≤2V (the Max value) and of course the correct current/voltage requirements.

For resistor values R2 (4.7M) tends to control the sensitivity, in this case if it's not firing you can up it. This is usually a dry hands issue. A readily available from RS 10MΩ should work for most folks, if that still isn't hitting consistently you could try dropping R1 from 47k to 22k (which is what I would actually start with), or even 10k also available from RS.

So simple (and cheap) to breadboard and try.

Some mosfets.

Digi-Key - IRLZ34NLPBF-ND (Manufacturer - IRLZ34NLPBF)

MOSFET N-CH 60V 14A DPAK - IRLR024

Power MOSFET - Power MOSFET Transistor - CSD16325Q5C - TI.com

This one is strictly 1V, should work fine even with a single 3.7V battery mod. Real low "RDS(on) max 0.0118Ω". Kinda small though.

STD40N2LH5 STMicroelectronics MOSFET Power