This instructable also details how to make functional curved circuit boards that can serve as a case and a circuit.
It also shows a fast, easy and inexpensive way to etch patterns and solder able traces on any simple circuit board.
The video shows how the lamp is turned on and off.
The intro Pic shows the touch switch lamp on the left and some other etched curved circuit boards that await components.
Step 1: How It Works
The touch switch circuit is based on the QT-113 integrated circuit. It works by detecting changes in capacitance. When it is first turned on it measures capacitance at its sensor plate. When a human touches or comes near to the metal sensor plate the capacitance is changed and the circuit turns on.
The sensitivity is adjustable so that at a lower setting it will require you to directly touch the sensor plate. At its most sensitive setting, it will detect your finger through paper, plastic, glass, or even a brick.
The larger the sensor plate the more sensitive the switch. The sensor plate is the triangular circuit board at the front bottom of the lamp.
Step 2: Materials
For etching curved circuit boards:
2 x-acto knives
clear shelf lining from Walmart
12"x12" Thin Scissor cut copper clad fiberglass board from Electronic Goldmine:
Line pattern fiberglass perfboard- Allelectronics:
QT113 IC from Saelig:
It appears that the qt113 is now only available in quantities of 4000 or more.
As of now, you can get a similar circuit the QT100 in small quantities. I got a chance to try one out and it is as sensitive as the QT113 and works fine. You can get a sot23-6 version here: http://www.saelig.com/IC3/IC3029.htm
You will however, have to add an additional circuit such as a microcontroller or another toggle circuit to keep the lamp on as the QT100 senses proximity but does not latch on and off.
2n2222 transistor and leds and resistors from Mouser:
Step 3: Making Curved Circuit Boards
Curved circuit boards can be easily made using the very thin circuit board material available at Electronic Goldmine. I have also seen it on EBay. It is copper clad fiberglass that is only .007" thick. It works like any other circuit board except that it is so thin it can be bent and because of the malleable copper cladding on both sides, it will hold its bent shape. It is quite flexible and can even be bent to form a ring that fits a finger. Bend it too much, however, and it will snap like a twig.
The bendable circuit board material can be etched by any conventional circuit board method that you prefer. The method I used for creating a resist is very simple and quick. I took inexpensive clear shelf liner which is sticky on one side and laminated the copper clad board between two layers of the vinyl shelf liner.
I then took a double bladed knife that I made (see pic5) by bolting two exact o blades to the sides of a fiberglass circuit board with the copper etched off. Pic6 shows how I cut out wherever I wanted to etch away the copper. You can cut curved lines or use a ruler to guide the double knife and cut straight lines.
pic7 shows the main body of the lamp laminated with shelf liner before cutting, etching and bending. It is 12" long.
You can of course etch very precise and complex circuit boards. I have chosen to used the curved surfaces to mount LEDs and inputs to create a simple circuit as the main body and structure. The detailed and more intricate part of the circuit is is a fast circuit module made on fiberglass perfboard. See next step.
Step 4: Fast Modular Circuits
I have started making most of my circuits modular so that they plug in and can be reused either on a breadboard or in a new robot. They plug in using .1" headers and sockets.
Pic8 shows the touch module that plugs into the lamp. It is made using fiberglass perfboard from Allelectronics that is the quickest way to make a permanent etched circuit board. You can drill away where you want the traces to end and use jumpers to complete the circuit. Pic9 shows the back of the circuit board where the switch circuit module plugs into the driver transistor board. To keep it thin I use magnet wire for jumpers on the back side of the circuit.
Pic10 shows the bottom of the lamp and the bent circuit board material that is soldered on to prevent it from tipping.
Step 5: Circuit Details
I used a standard USB plug from an old camera. If you cut off the smaller plug which goes to a camera or other device you will find four wires. The black is usually the ground and the red is the +5 volts that USB supplies. Check with a voltmeter to make sure you have the right wires for power. The other two wires are for communicating with the PC and can be ignored.
pic11 shows the details of the circuit. The qt113 drives a 2n2222 NPN transistor which turns on the 5 LEDs which are wired in parallel (pic11b). The base resistor limits the current to the LEDs to less than 100 ma. I used surface mount white LEDs but any white LEDs could be used.
With pins 3 and 4 to ground the switch turns on at first touch and off at second touch. If you connect 3 and 4 to +5 volts the switch will stay on only while you are near or touching the sensor.
I originally etched the back of the 12" lamp circuit board to be the sensor plate. Because the circuit board is so thin, it created excessive capacitance and did not work. So I did a workaround and mounted the triangular plate at the front base of the lamp.
Step 6: Possibilities
CONTROL OTHER DEVICES
The touch switch is used here to turn on a few LEDs. If you replace the LEDs with a 5 volt relay it could be used to turn on any device that the relay could handle. You could turn on AC or DC devices.
PORTABLE TOUCH SWITCH
While this LED lamp is USB powered, it could also be made more portable by using three aa batteries as the power supply.
CONDUCTIVE FABRIC TOUCH SWITCH
This touch switch circuit is ideal for use in conductive fabric switches where the touch switch plate is a hidden grid of conductive fabric or thread and you only have to touch near or on an area of fabric to turn on a wearable circuit.
LIGHT WEIGHT STRUCTURES
pic12 shows a back lit curved circuit board that has been etched with the same pattern on both sides. Because the circuit board fiberglass is so thin, LEDS can be mounted behind the board and will glow trough. This curved circuit material is ideal for wall lamps or other hanging circuits.
HEAVIER DUTY STRUCTURES
You can make the structures stronger by laminating two bent forms together or gluing a layer of fiberglass on the back with epoxy. Copper wire or other circuit board material can also be soldered to the main structure to make it sturdier.
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