LED Sensor Array

[sanjed]

if you have a webcam or or other video source, then have that watching what you are doing with the array, have that image on display in a window, then screencap the whole screen,and crop out the bits you don't want.

if you have a windows machine, windows media encoder 7 is fairly good for that sort of thing, as it will compress the video on the fly to a wmv.

the video you have already posted is fine if you apply imagination, it shows readings being take from a source, we just have to imagine you swishing your finger over the array.

you could maybe slide the bar on the encoder further over towards quality though.

[justDIY]

Greetings,

This project is still alive.  I've been fighting some firmware and hardware issues, but that's all cleared up now! 

I have a new pic handling my A2D, it is capable of reading ten sensors, and the breadboard I'm using has room for four of these slaves, so I could potentially have a 40 sensors, but thats not very practical... the way a breadboard is layed out electrically, I'm only able to build 2xN arrays.  I've found that ten sensors actually offer a decent resolution.

I'm working more on doing useful things with the data.

Currently, I have the master pic doing some conditioning of the data, before feeding it to the host computer.  It sets a baseline value for the sensor array at startup, and then computes the state of each sensor based on the current value versus the baseline.  Then it outputs a binary state, sensor is ON or OFF ... the host computer uses this data to toggle a series of checkboxes ... but thats just for starters.

Eventually I want to offload the data conditioning to the slaves themselves, to cut down on bandwidth usage on the i2c bus, and I have quite a bit of code space available in the slaves, so I'll probably have a couple of different conditioning scenarios... like binary output (digital) and a couple different analog output modes (real time, average, inverted, etc)

The next building block I want to make is how to turn a string of ten 16bit numbers into a scroll bar type device.

I have observed while playing with the numbers, the sensor values decrease as more light strikes the sensor... but, as the object being sensed, that is, my finger moves directly over the sensor, the value increases, since now my finger is sheilding the sensor from light, rather than reflecting light into it (the sensor is blind to its own light)... so to really know the position of my finger, I'd need to look for a sequantial pattern, low higher low, or something like that.

[justDIY]

Code-Writers-Block 

I'm having some trouble coming up with just how to turn a string of numbers into a usful user interface application... Anyone with any ideas?

Analog real-time output:

no objects on the array:
23000 23000 23000 23000 23000 23000 23000 23000 23000 23000

object at one end:
9000 9000 9000 23000 23000 23000 23000 23000 23000 23000

object at the other end:
23000 23000 23000 23000 23000 23000 23000 9000 9000 9000

basicly, an object on the array causes those sensors to report a lower voltage... the numbers above are made up, but they are realistic numbers.

alternately, I can condition the data into a real time binary state output:

no objects on the array:
0 0 0 0 0 0 0 0 0 0

object at one end:
1 1 1 0 0 0 0 0 0 0

you get the idea.

The binary state works great for "buttons", and I have a simple app which reads the array as a state of 10 buttons... which would allow any sort of up/down control or data input, but not an analog control like a knob or slider.

[justDIY]

Work Harder, Not Smarter

Here's some ramblings I keyed into notepad...  I'm trying to figure out how to get more sensors with fewer leds.  I poured the substance of my thoughts out on my blog, but wanted to get some engineering feedback here

16 leds per slave:
led anodes driven by two 74hct573s, all data inputs ganged together so all outputs are high or low, tristate line held low (disabled), latch line held high (disabled)

PIC pins required 1: LED pins driven 16: Total Pic Pins 1

led cathodes driven by two 573s, all data inputs ganged together so all outputs are high or low, tristate line connected to pic, latch line held high (disabled)

PIC pins required 2: LED pins driven 16: Total Pic Pins 3

led cathodes sampled by 16:1 analog mux CD4067, each led cathode connected to a mux input, mux output connected to pic ADC input, four address lines connected to pic, enable line connected to pic.

PIC pins required 6: LED pins read 16: Total Pic Pins 9:

Total LED pins managed 32: Savings 32 - 9 = 23 pins

An adding additional 573s to the anode and cathode drivers requires no additional pins and adds 8 or 16 more LEDs.  Adding an additional CD4067 or 4051 mux requires 1 more pin on the pic for the enable line... so 32 more leds could be added for a total of 10 lines required on the PIC.

[Rob]

I'm having some trouble coming up with just how to turn a string of numbers into a usful user interface application... Anyone with any ideas?

The thing that strikes me is that you have ample CPU cycles available. So you can do clever things along the lines of what the QProx chips do.

The simple thing is reading the position data. But if you calculate/approximate the deriviatives of it, you can get a velocity vector too, and that could control something. So to revisit your examples

23000 23000 23000 23000 23000 23000 23000 23000 23000 23000
minus
9000 9000 9000 23000 23000 23000 23000 23000 23000 23000
equals
14000 14000 14000 0 0 0 0 0 0 0

which is the derivative.

Does that line of thought give you any ideas?

(as for the immediately preceding post, I have no idea what you're on about  )

Added: I read te linked blog post and now I get it--I'll share some thoughts presently.

[justDIY]

The madness begins.... again?


click for a supasize version.

this is the start of a schematic for a 6x5 array based on my new idea for interfacing the array to a microcontroller... it has a lot of work to go yet!

[justDIY]

Cadsoft Eagle is a great tool...  nearly finished in no time!

Here is the schematic, nearly complete:


click for a really huge version (134kb, 3028x2056)

The ICs along the top are the anode drivers.  The ICs along the bottom are the cathode drivers attached to current limiting resistors.  The ICs on either side are 16:1 multiplexers, connected to the leds in sequential order, each handling three sets of five leds.  I still need to add the microcontroller and some connectors.

I realized while wiring the schematic... I could probably use a pair of mosfet transistors, one N, one P configured for push-pull logic, in place of the anode drivers.  Then I can wire the LEDs as a common-anode array, cutting down on the complexity.  The LED cathodes need to remain separate, since the a2d mux needs to read each one individually.

Hehe ... a light bulb just came on in the 'ol brain-box ... I wonder if they make common-anode led matrix displays, off the shelf?   I know they have anode row cathode column matrices, but that doesn't work for me since the cathodes are not separated.

[Rob]

Someone's been busy...

[ReefRaff]

hmm, I'll let ya know when I know what you just said. LOL

[justDIY]

alright - lets just chalk those last few posts up to too little sleep, too much thinking.

Here's a more humble beginning ... a 4x5 led matrix, wired as anode column, cathode row.

I'm not entirely sure how I'll interface with it... but it won't be too much to make up a few, and even if I can't use 'em for this project, they'll probably be neat somewhere else.



Of course, working at 2am is not without its risks... after I had completed the PCB layout, I was in the process of making TIFFs, so windows detected the time and the fact I hadn't saved recently and gave me a good 'ol GPF ... "We're sorry, eagle.exe has encountered an error and needs to close."

So, all I have right now is that GIF file.  But I should be able to re-draw it quicker the second time around, after some sleep.


click to download 300DPI TIFF format of pcb, should come out the correct size if printed at 300 dpi

The pads along the bottom of the pcb can work two ways ... either you can drill them (or not) and use ribbon cable or some other mutliconductor wire, or use some 0.100 spaced pin headers, surface mounted parallel with the board, then you can plug your led matrix veritically into a breadboard using only 9 spaces

[az1324]

Hey I'm very interested in putting together a slider type linear control using a single row of 10 or so leds.  Do you have some working code and hardware diagrams for that situation?  Also, does this work with blue leds too?  Thanks.

[justDIY]

Hey I'm very interested in putting together a slider type linear control using a single row of 10 or so leds.

I think you'd have better results using a double row of emitter detector pairs, then you don't have to worry about switching between emitting and detecting.

Do you have some working code and hardware diagrams for that situation?

sorry, no - i gave up on software development after realising as neat as this tech is, it isn't practical, or can't be done easier with something like an infrared emitter detector pair.

Also, does this work with blue leds too?

in theory, any LED should work.   in the real world, I was unable to get good results with anything except red and yellow leds.

btw, Welcome to our forums!

[timmmccoy]

Hi guys,
i joined the boards after being directed here by justDIY's blog after reading about his LED endeavors....
i'm not a very accomplished EE (if i can even call myself that) im 16 and my dad taught me all i know about electronics although its been about 20 years since he last drew up a schematic.......
i was thinking about the button idea though and i thought you could do it this way:
you could have a 2x2 matrix of LED's (behind the touch switch cover of course) two would be red and two would be IR so when the switch was off it could listen to the IR LED's and when it's on it could turn on and listen to the red LED's i imagine the same could be used for sliders and such........ i myself would like to start experimenting with this as well as getting into microcontrollers..... any good suggestions for MCU's, programming languages, compilers... etc.
Any help would be appreciated,
Timm-McCoy

[payce]

*First post!* 

So, first of all I wanted to bring out my biggest respect to JustDIY for such a long breath and getting into this (really not easy) topic this deep! Really great work up to now which I loved to read up to here!

That topic also got me going again, so I think I´ll start putting something together like you did, perhaps with some other implementation ideas, let´s see. I would be F****ING happy to bring it as far as you already did, anyhow. *slimedrippingoff* 

Greetz!

[Rob]

Welcome to the boards, payce.