Archive for the 'Interface' Category
Hello readers from MAKE: as well as all other readers :)
My prototype touch sensor worked so well, that it hasn’t needed much changing. I sent the design off to Custom PCB, and less than a week later, I had a pile of circuit boards waiting for me.
I changed the layout around a little, mostly adding a 2×8 header for accepting a ribbon cable style connection. The header combines power, ground and outputs into a single connection, making it easier to connect to the main board of my larger project (sprinkler controller). Each touch output is paired with a ground wire, which I suppose makes it more resistant to interference. The caps I used this time are polyester film 220 nF, doubling the amount of capacitance compared to what was used on the prototype.
Yes, the ugly piece of plexi is still ugly. Don’t worry, it will be hidden from view. In the final configuration, this board and its plexiglas spacer will be inside a plastic project box. I’ll have a laminated “keypad” overlay affixed to the outside of the box so I can see where the buttons are. The spacer will be flipped around, going on the solder side, giving me enough clearance to flush-mount the sensor with the wall of the box. Flush mount is very important, as even the slightest air-gap will ruin the proximity sensing effect.
Nothing much to see solder side… a few smt passives set options on the chip, as well as decouple and filter the incoming power. The big resistor limits current for the meager power led which no one will ever see once the board is in use.
I’m very close to finishing the larger irrigation control project, hopefully sometime this week! Thanks for reading!
Popularity: 80% [?]
Presenting “6buttons”; a simple six button keypad based on the QProx QT160 charge transfer proximity sensor chip.
More details to come later, wanted to get some pictures and video online tonight.
simple schematic – i plan a “backpack” pcb which will provide some visual feedback, a clicking noise and translate the six outputs into an i2c bus device.
the brains of the operation, this chip does all the work. special mylar capacitors are required for it to work properly. i tried cheap-o ceramics with terrible results. the orange thing is a 10mhz resonator.
the “buttons” are printed out on plain paper, using the silkscreen layer from my pcb layout program. the capacitive dielectric is provided by the FR4 pcb material, the paper and a 1/8th inch thick layer of plexiglas; I guess you call that a multilayer capacitor!
the sensors are simple copper rings, which radiate the electrostatic field this chip uses to sense proximity. a ground plane pour around the IC helps to minimize cross-talk between sensor channels and prevent stray fields from detecting proximity around the chip itself. the capacitors near the chip also sense proximity and will need to be shielded with aluminum foil or something.
forgive the craptastic music in the video!
edit: also read Capacitive Sensing Continued
Popularity: 65% [?]
The firmware for my LED Sign / Clock project is taking shape. I’ve worked out my initial wishlist of features, and put together a basic menu structure. I figured a menu is the easiest way to access a lot of options, while only relying on two buttons.
The basic menu consists of options for setting the time and date; minute, hour, day, date, month, year. The basic options are pretty self explanatory. I have also planned some more advanced options:
1. Adjustable display brightness – Varying the duty cycle and refresh rate of the matrix can effect its brightness. I need to make a simple scale for these variances to allow for two or three brightness levels.
2. Adjustable scrolling speed – The program draws the same information several hundred times per ’scroll’, changing this counter affects how fast the display appears to scroll.
3. Selectable time format – User can choose between 12 hour AM/PM time and 24 hours ‘Military’ formats
4. Message Mode – User can enable / disable scrolling messages as well as display a single message, a random message or messages in sequence.
Other than that, the code is still pretty basic. I’ve completed a bunch of internal fixes, like the scrolling code now handles messages of variable lengths. up to sixteen characters. I’ve also created i2c eeprom reading routines to extract menu prompts and other text strings I’ve stored in the eeprom to save flash space on the chip.
Popularity: 52% [?]
If necessity is the mother of invention, being cheap must be like a step-father or uncle or something?
I needed some level shifters / line drivers that I could easily use on the breadboard for microcontroller projects. Rather than give some other entrepreneur $10 for their version, I made my own.
Nothing particularly special here, aside from the cool factor added by the two LEDs which light on RX/TX events. The chip is a standard MAX232 clone, and I’ve got five 1uF ceramic caps mounted on the back side. The leds are driven by some SOT-23 transistors. To make things simple, I stuck the pin header through the board the “wrong way” and forced the pins almost all the way through their plastic spacer / retainer. This way the unit plugs right into the breadboard, and lays there real nice, even with a heavy serial cable attached.
So far so good, it works well with my bootloader at 115kbps, so I figure that’s good enough!
EDIT: Eagle SCH and BRD files available here (7-zip format).
Popularity: 18% [?]
The “core” building-block I mentioned in my last post is nearing completion, at least, the software.
I have my microcontroller handling “switch emulation” tasks. It can emulate either group of momentary switches or a group of toggle switches. Response time is real good in a dimly lit room, and it works decently well even with the overhead fluorescents turned on.
Right now I’m working on a basic keypad PCB I can throw together, for a ‘proof of concept’ prototype. The first keypads will likely only support 6 keys, and I’ll build from there. Six keys requires twelve LEDs, six of them need direct and discrete anode and cathode connection to the microcontroller. The other six LEDs are providing bias light for the sensors to “see”.
I should have a video up tomorrow of the breadboard in action, and hopefully some pcb’s by next weekend.
Popularity: 65% [?]