My (probably not so) new idea for a diy pedal display

[birt]

if you are only using 1 resistor for more leds you have to recalculate it. the current is divided into the parallel leds.

i just checked some displays i had lying around. i have 4 working 7 segment displays the size of a 556 ic. i need already 3 to make the word OFF...

i also have one big 7segment with small light bulbs instead of leds. it's old and it looks cool :p

and then i have 15 small ones that don't seem to work. i can find the pinout and voltage drop but there is no light when i give em power. really weird.

[ugly_guitar_guy]

Ok, so here's my understanding of the simplified idea, if I'm getting this correctly. I did this quickly so I didn't include any diodes but I would figure that any shared LED from both powered circuits would require a diode on both sides of the annode to keep power from leaking to the other side? That's 20 diodes....

[frequencycentral]

Ok, so here's my understanding of the simplified idea, if I'm getting this correctly. I did this quickly so I didn't include any diodes but I would figure that any shared LED from both powered circuits would require a diode on both sides of the annode to keep power from leaking to the other side? That's 20 diodes....

I don't think you would need any diodes - a 7 segment display is just 7 seperate LEDs right - with a commom cathode (or is it anode)?

[ugly_guitar_guy]

Ok, so here's my understanding of the simplified idea, if I'm getting this correctly. I did this quickly so I didn't include any diodes but I would figure that any shared LED from both powered circuits would require a diode on both sides of the annode to keep power from leaking to the other side? That's 20 diodes....

I don't think you would need any diodes - a 7 segment display is just 7 seperate LEDs right - with a commom cathode (or is it anode)?

Well the ones that I have are commom cathode (that's why I'm routing power in), and if you watch the video there's some power bleed over that I explained a couple posts back that some diodes would probably solve. I might have to breadboard this idea tonight just to see how it works.

[birt]

Ok, so here's my understanding of the simplified idea, if I'm getting this correctly. I did this quickly so I didn't include any diodes but I would figure that any shared LED from both powered circuits would require a diode on both sides of the annode to keep power from leaking to the other side? That's 20 diodes....

in the setup you have drawn here everything would be lit eather way the switch is.

right now you have 2 circuits. but you need 3. one for the common parts (always on, so you hard wire them) and 2 with seperate parts so you switch between both words. the switched circuits can't have any shared connection.

i can't explain it any better than this


oh and something about parallel leds:

parallel leds with ONE current limiter (like what i suggested and what you have drawn now) can only be used this way if they are the same leds. that means same color, same voltage drop, same current consumption. so in these displays i don't think there would be a problem.

the reason for this is that if a circuit with 1 led needs 20mA, a circuit with 3 needs 60mA. if the leds aren't identical one led might get too much current. so better practise is to allways add leds in series or with a current limiter each. in these displays i am pretty sure the leds are identical so we can make an exception :p

[ugly_guitar_guy]

in the setup you have drawn here everything would be lit eather way the switch is.

right now you have 2 circuits. but you need 3. one for the common parts (always on, so you hard wire them) and 2 with seperate parts so you switch between both words. the switched circuits can't have any shared connection.

i can't explain it any better than this


oh and something about parallel leds:

parallel leds with ONE current limiter (like what i suggested and what you have drawn now) can only be used this way if they are the same leds. that means same color, same voltage drop, same current consumption. so in these displays i don't think there would be a problem.

the reason for this is that if a circuit with 1 led needs 20mA, a circuit with 3 needs 60mA. if the leds aren't identical one led might get too much current. so better practise is to allways add leds in series or with a current limiter each. in these displays i am pretty sure the leds are identical so we can make an exception :p

OK, I think I understand now. I'm going to draw that up...

[ugly_guitar_guy]

Ok, here it is. 3 circuits. Just have to figure out what value of resistor to use...

[birt]

let's say the forward voltage is 1.7 (red leds) and you want 18 mA for each led (on the safe side...)

then you need 90mA for the OFF circuit. thats 82ohms.
36mA for the ON circuit. 220ohms.
162mA for the common. 47ohms. it might be better to split this up and use 2 or 3 resistors here.

[ugly_guitar_guy]

let's say the forward voltage is 1.7 (red leds) and you want 18 mA for each led (on the safe side...)

then you need 90mA for the OFF circuit. thats 82ohms.
36mA for the ON circuit. 220ohms.
162mA for the common. 47ohms. it might be better to split this up and use 2 or 3 resistors here.

2 or 3 resistors along with the ones shown above or am I on the wrong track? Can you illustrate?

[birt]

tou have 9 leds in the common circuit. you could split that up in 3 parallel circuits with 3 leds. each of those circuits needs 54mA. so you use 3 150ohm resistors.

the more leds you put parallel with the same current limiter the more chance you have that things will be unbalanced.

you started with a setup that had 25 resistors. now you'll have 5. not bad hm? :p

[ugly_guitar_guy]

tou have 9 leds in the common circuit. you could split that up in 3 parallel circuits with 3 leds. each of those circuits needs 54mA. so you use 3 150ohm resistors.

the more leds you put parallel with the same current limiter the more chance you have that things will be unbalanced.

you started with a setup that had 25 resistors. now you'll have 5. not bad hm? :p

Ok, gotcha. So here's what I'm looking at now (I believe). What value resistors would you recommend for the other 2 (since one section has 2 and one section has 5?

[birt]

82Ω and 220Ω as i said before. you can just calculate it or use an online calculator...

[pjwhite]

This project reminds me of something I made for halloween a few years ago.




The IC on the back is a 555 timer which toggles the numbers between 1999 and 1900 every couple of seconds.  I think I used one resistor per LED segment.

[ugly_guitar_guy]

82Ω and 220Ω as i said before. you can just calculate it or use an online calculator...

Oh, sorry...    I'm going to put this together tonight and see how well it works out. I guess I'm gonna have a lot of short lead 1K resistors lying around now, haha. Thanks for all your help birt. I feel like such a newb with this stuff sometimes...

[birt]

I feel like such a newb with this stuff sometimes...

me too

i believe this is the very first topic where i could really help someone

[ugly_guitar_guy]

birt you were spot on! This display layout has been tested and confirmed now. Just check out the video link below:

http://www.youtube.com/watch?v=xmh7qxRSAPQ

No more ghosting and everything glows nice and evenly bright. I'm going to have my new pedal that this is going in done by next weekend so I'll share it once it's done. Thanks again!

[tommy.genes]

You should mount that under the enclosure paint as is shown in these photos.



-- T. G. --

[frequencycentral]

You should mount that under the enclosure paint as is shown in these photos.



-- T. G. --

Thats awesome - how did you do that???

[ugly_guitar_guy]

That's fricken brilliant! How did you do that?

[iaresee]

That's cool. Reminds me of a Police album cover.