Hi,
for my current project I will have to design a PCB which will hold a controller (maybe I will use some ATtiny oder ATmega's, they are cheap... But the STM32F100 series is also cheap :) ) which is interfaced by a SPI interface and some capacitive touch buttons (using http://http://www.atmel.com/dyn/products/devices.asp?category_id=170&family_id=702&subfamily_id=2259: Atmels QTouch). I also would use a PIC but I've never done anything with it... :).
The plan is to have some simple buttons (maybe with LED in the middle) and one slider. I would like to have a wheel slider (e.g. for menus) but I don't know if this will fit the project.
Maybe this is a thing in which other people are interested? Maybe this could be something for DP?
I chose QTouch at this point because it's damn simple and only consists of one resistor, capacitor and electrode for one touch field. And it can be implemented with a few lines of code on every microcontroller which supports putting it's pins to a floating state.
Any suggestions? Any things you would like to see?
Nils
If you decide to go with pic, some of the 24f series have internal peripherals to support capacitive touch.
I've for one would like to see this used in a "remote control" application with backlit buttons using back-fire smd leds. I have been pondering this but haven't come up with a good board routing of the buttons and leds.
That's a good hint, thank you a lot. My only concerns about the PIC's are the fact that I would have to use two different toolchains (STM32 = Eclipse + GCC, PIC = proprietary software). Also I've never done anything with the PIC's and I don't know if interfacing capacitive touch buttons is the right thing to start with.
On the other side: The PIC18F45K22 seems to support up to 28 analog channels and with mTouch that means up to 28 capacitive touch buttons... and it's only about 4€ @ 1. That's very nice :).
I have some other parts in the project where a SPI -> UART conversion is needed. This is on expansion boards so every board holds it's own controller. Maybe I could also use a PIC there instead of an atmel (cheap) or STM32F100 (also cheap ;) ).
Anyone has a reason why I should use a PIC for this and not a STM32?
Nils
There were a lot of different mcu's there.
Without knowing what you are trying to make, are all those really needed? Couldn't you just use one for all those functions?
As for which type to use, it depends on the time you would like to spend on the project.
If there's not much time to spare, use a mcu you are comfortable with.
But if this is a long running project, step out of the comfort zone and learn something new. It is always fun.
Yah I know I. I'm just lazy :D. I think I will take a closer look at the PICs and then decide if I will use them :).
The idea of a remote control is nice. Did you think of a "true" remote control for TVs with IR-code learning or did you thought of a simpler application?
Nils
Yes, an IR remote to be built in under a glass pane in the coffee table, to control TV, DVD etc.
Thought I could use the IrToy for finding out the codes and then hardcode them into firmware.
[quote author="honken"]I've for one would like to see this used in a "remote control" application with backlit buttons using back-fire smd leds. I have been pondering this but haven't come up with a good board routing of the buttons and leds.[/quote]
What is a back-fire LED?
Livid Instruments designed their own rubber button pads with room for an SMD LED or two in the center. These work with normal to-side-only SMD parts, so you don't need to do anything special for the LED. The buttons might be too big for a thin remote control, though, so unless you like a substantial-feeling milled aluminum case you might look for another button maker. Buttons come in 2x3+1, 4x4, and 8x8 groups, but you can actually cut the rubber between the buttons to use fewer of them. These buttons are part of their Builder series (http://http://shop.lividinstruments.com/builder.html), and seem to be very reasonably priced. They also offer a PIC-based 'Brain' (which I designed), but it's rather expensive compared to Dangerous Prototypes platforms. The 'Brain' has 64 analog inputs interfaced to a PIC18, so it might be appropriate for a touch interface.
As for the whole question of whether to tackle your first PIC project or continue with what you know, I really don't think there is one right answer. I learned many 8-bit processors, but PIC18+USB was the first where I really designed something big and powerful. Thus, I have an affinity for PIC, and really enjoy how many projects here use PIC. But I have a strong suspicion that if I had chosen to start with AVR, particularly one of the newer USB-capable versions, I would love AVR just as much. Personally, I can't wait to find a project which needs one of the AVR+USB chips. I probably wouldn't bother with Arduino, because I want the USB peripheral, but AVR has some really nice options, and I have been studying them lately.
I think you can do anything with AVR that you can do with PIC, provided that you select the correct AVR chip for your project.
[quote author="rsdio"]
What is a back-fire LED?
[/quote]
A smd led with its lens pointing downwards, into the board, shining through a hole on the other side.
The whole exercise with capacitive touch is to get a totally flat input surface.
[quote author="honken"][quote author="rsdio"]What is a back-fire LED?[/quote]A smd led with its lens pointing downwards, into the board, shining through a hole on the other side.
The whole exercise with capacitive touch is to get a totally flat input surface.[/quote]Ok, so my pointers to huge rubber buttons is totally unrelated to capacitive touch. Oops.
Thanks for the education on back-fire LED tech. That seems rather cool, since putting extra holes in a PCB usually doesn't even cost extra.
you may want to take a look at cypress Capsense Express chips (cant add urls lol). They offer easy to use capasitive touch technology that can be configured by i2c and stored in onboard nonvolatile memory and features autocalibration so there is no need to program or calibrate the chip. It needs no external resistors or capacitors all you need to do is design a good pcb layouth and you are on the go. Its the chip i use for almost all of my proyects that require touch buttons.
If u want more power, you may want to take a look at cypress's CapSense®Plus chips wich offer up to 44 capacitive buttons and 8 sliders, support for LED effects, proximity detection and water rejection; all with an integrated 8bit PSOC core.