LED "capacitance" won't get lower

[flotulopex]

Okay skimask,

I'll try to explain clearly what I'm doing - or trying to achieve.

I have three 7seg-LEDs (three "digits") connected to a 16F88 @ 20MHz and I want them to act as buttons as well.

These three 7seg-LEDs display random numbers whithout any decimal point so I use this Dot-Point as the sensor for each 7seg-display.

I couldn't find exactly in your code how you compensated the effect of the surrouding luminosity but you have surely noticed that, in a dark environment, the discharge time of the LEDs raises drastically.

Thus, the "scanning time" until the "darkest" (or "pressed") LED is detected can be quite long. In my experience, it can take over a second.

My idea is to compensate the surrounding darkness by dropping the LED's Dot-Point voltage and hence, reduce the charging/discharging cycle.

Currently, for testing, I'm working with three digits but my final project would have ten digits (key-pad) so the time to analyse which button is pressed is important.

Voilà. Hope this helps for understanding...

It's far too amazing so I can't give-up now; got the same kick as you

[skimask]

I have three 7seg-LEDs (three "digits") connected to a 16F88 @ 20MHz and I want them to act as buttons as well.

I'm wondering if the case of the 7 segment displays isn't killing your light input, ya know, the covering over the segments themselves...

I couldn't find exactly in your code how you compensated the effect of the surrouding luminosity

I just kept scanning the LEDs, keeping track of the highest and lowest result every returned. Just for arguments sake, let's say the highest result I've gotten is 500. The next time I scan, the highest result is 498, I might subtract 1 from my last known highest result. Same thing for the lowest result. I don't rely on absolute numbers. I keep track of the range of inputs, recheck the inputs, see if the same input is the highest more than once, then select the most probable out of the bunch.

My idea is to compensate the surrounding darkness by dropping the LED's Dot-Point voltage and hence, reduce the charging/discharging cycle.

I wonder if going the other direction, lighting it up a bit more would be better.
And it is a neat little thing to play with...
All in all, I think it's the 7 segment display itself that's going to cause you problems.

[Ioannis]

I have not yet dealed with this kind of touch sensors but have an idea for flotulopex: Use all 7 segments, or at least some of them, to measure the ambient light instead of the dot only. I think you will get more reliable data.

When I have the time I'd love to experiment on this.

Ioannis

[skimask]

I have not yet dealed with this kind of touch sensors but have an idea for flotulopex: Use all 7 segments, or at least some of them, to measure the ambient light instead of the dot only. I think you will get more reliable data.
When I have the time I'd love to experiment on this.
Ioannis

There ya go...you could use some of the lit segments along with the dot. At least you'd get a better average. And some of the light from other lit segment bouncing off your finger might help the other 'sensing segments' give you better numbers.

[flotulopex]

I did so already (using all segments).

There's no big difference with using the dot-point only.

I spent around 20 hours on making tests with different LED configurations and finally, I think the best way to handle "compensation" would be to influence the LED's capacitance.

But up to now, nobody could give me a hint on how to achieve this...

[skimask]

I did so already (using all segments). There's no big difference with using the dot-point only. I spent around 20 hours on making tests with different LED configurations and finally, I think the best way to handle "compensation" would be to influence the LED's capacitance. But up to now, nobody could give me a hint on how to achieve this...

If, in fact, it is achievable...which I don't think it is. Sure you can change the 'charge voltage', but it'll still discharge at the same rate. You can change load resistance, which will also affect your charge time.
Maybe you might need a different type of display, maybe a different color?
How about some sort of constant overhead light (front lighting?)...
You've got a neat idea...and I'm thinking...still...and it hurts

[Ioannis]

skimask's keyword is "rate". That won't change with voltage only.

Given the voltage and the load on the capacitance of the LED the rate will always be the same.

Only by changing the load presented to the LED will change the rate. And now it came to me an idea. Why not put a second pin of a PIC in parallel to increase the load when you want and then set it at tristate again? May be and a third one?

Ioannis