Idea for Christmas gift for my gf need advice

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beatzmikee

New Member
Ok so my idea is to on a proto board i have about 18 leds lined up to make a heart... i want them all to flash when she presses a touch sensor (much easier then a press button) and im not really sure how to tackle this...
also there has to be a simpler way to control all the leds with out hooking each led up to a resistor and then to an output? if possible i would like to do it all with a 08m2 im almost open to anything
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boriz

Senior Member
A lot depends on the LEDs. Datasheet? And what you mean by 'flash'. (all at the same time or in a pattern?)

If I assume Red 10mA, 1.7v Vf, all flash together, here's two options.

18 could be driven all in series if you can provide over 30v. Simple enough to do with an inverter circuit. Google 'joule thief'. For the basic circuit. Can be simply modified for 30v with a bigger coil and a little more drive current. Prolly get away with no resistors at all.

Or you could drive them in parallel from a single output pin. One resistor each. Using a transistor to boost the current to over 180mA.
 
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beatzmikee

New Member
i mean flash in a pattern.. i was thinking a 555 timer but thats just blinking.. im actually using green (her favorite color) they are 3.3v 20mah yeah all blink at the same thing then a chaser then fade (pmw) looks great on my breadboard but thats with my 28x1 and i dont want to use that.. i thought about transistors but thats not what im looking for either lol.. picaxe seems to give me exactly what im looking for.. i want them to fade chase then blink then turn off so it doesnt use alot of the batteries. i was looking at the MAX7219 chip never used this chip before i dont have alot of time before Christmas u know..? lol i would love a very simple solution.. maybe even one that doesnt involve a picaxe
 
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chipwich

Member
I imagine that wiring the LEDs in series and driving off 30v is probably inconvenient (assuming your project is powered by batteries), but is possible.

Your method of wiring each LED to an output has some limitations. Each output can sink about 20mA, and the entire PICAXE can only sink about 90mA total, so don't expect one PICAXE to light all of the LEDs at once. You could build a light chaser using a 20M2, making sure you don't exceed the 15 outputs, and don't turn on more than 4 outputs at a time.

You could also use a buffer of some sort. Discrete transistors will create much wiring. The MAX7219 you mentioned looks reasonable. But if you want cheap and easy, consider a basic ULN2803 or ULN2003 Darlington Driver IC. You can drive 2 or more LEDs at a time from an output as the IC will sink quite a bit of current. You will need to use current limiting resistors on the LED strings, unless the sum of the forward LED voltages (in a string) add up to your source voltage. The Darlington IC can also control multiple transistors from a single input, or a small number of inputs; so you can use an 08M2.
 
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westaust55

Moderator
chipwich said:
You will need to use current limiting resistors on the LED strings, unless the sum of the forward LED voltages (in a string) add up to your source voltage.
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There should always be a current limiting resistor unless the controller chip has inbuilt current regulation (constant current).
Voltage even at the Forward Voltage of the LED/Diode will not prevent excessive current flow.

The MAX7219 will allow you to expand up to (8 * 8 =) 64 LED's if you so desired with each capable of seaprately controlled on/off - that would allow you to fill in the heart shape as well.
The MAX7219 only needs 3 PICAXE outputs so as mentioend, an 08M2 with 2 kbytes of program space could give a very reasoanble display sequence.
 
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beatzmikee

New Member
i never planned on using all LEDs at one time if anything i wanna just use a chaser or something along those lines i like the MAX7219 idea but it seems that it will take too long for it to arrive before Christmas... i considered a 555 timer actually lol i have alot of 20m2 (my favorite) and my new one looks better im using 23 LEDs and i figured i would light each one up individually about 8 LEDs per segment.. that should make things simple and putting a loud speaker on it and play a Christmas ring tone with it when she presses the button.. i have a new pic of my changes. Any ideas of how i could accomplish this? is lighting up 8 leds too much for a 20m2 to handle? i would have limiting resistors on each segment.. i was thinking like around 470k ohm?
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PaulRB

Senior Member
The 20m2 has the same 90mA overall current limit as the 08m2. 8 LEDs at once would have to be limited to around 10mA each, so ok but not dazzlingly bright. You really need some driver transistors. Then you could just use an 08m2 and your original design. You could use a pnp transistor controlled by the pwm output to drive the anodes, and 3 npn controlled by 3 other outputs (would need to use serial out pin) to control the 18 LEDs in 3 groups of 9 in parallel.

Paul
 
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beatzmikee

New Member
What do you think would be the best driver, or a common one that I could pick up at like a radio shack:) ? Can I still have pwm with a driver?
 
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nbw

Senior Member
I could recommend a soon-to-be-announced reasonably-humorous book of electronics cartoons? ;-)

Great for those gifts for the woman who has everything. Well, nearly everything. If she had everything, she'd have the book already. Etc and so forth.
 
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MPep

Senior Member
nbw said:
I could recommend a soon-to-be-announced reasonably-humorous book of electronics cartoons? ;-)

Great for those gifts for the woman who has everything. Well, nearly everything. If she had everything, she'd have the book already. Etc and so forth.
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Oh crikey, there is a comedian amongst us !!!! :)
 
fernando_g

fernando_g

Senior Member
beatzmikee said:
What do you think would be the best driver, or a common one that I could pick up at like a radio shack:) ? Can I still have pwm with a driver?
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At least in my neck of the woods, Radio Shack has become irrelevant for components.

You still have time. Even with standard shipping, you can get stuff within a 3 business day timeframe. Faster if the selected vendor is near where you live.

I have just purchased some stuff from allelectronics. Ordered them on a monday, were home on thursday. They are in southern California, and I'm in Texas.
Sometimes when I order stuff early in the morning from Mouser (which is also located in Texas), they are at home on next day's evening.

Get yourself some ULN2803 octal drivers. They have all the transistors and resistors in a single IC package. Makes life a lot easier.
 
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Paix

Senior Member
Buy her an oscilloscope or another bit of test kit, but if you do so, make sure that she is going to marry you, or you might regret it . . . :)
 
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geoff07

Senior Member
Great idea and all that but perhaps better if it came attached to a bottle of Chanel No5. It is difficult to understand why, but somehow the ladies don't seem that interested in Picaxes.
 
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PaulRB

Senior Member
beatzmikee said:
What do you think would be the best driver, or a common one that I could pick up at like a radio shack:) ? Can I still have pwm with a driver?
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I'm not a transistor expert, so wait until someone who is (eg Alan) to approve my recommendations:

BC327 PNP

BC337 NPN

Yes, you can use pwm with a transistor driver.

Paul
 
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beatzmikee

New Member
I really like that idea of a hear pulse maybe I could drop out the idea of a speaker but after the light show have it sync to her heartrate :) how would I go about doing this?
 
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AllyCat

Senior Member
beatzmikee said:
I really like that idea of a hear pulse maybe I could drop out the idea of a speaker but after the light show have it sync to her heartrate :) how would I go about doing this?
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Hi,

With great difficulty! Perhaps the easiest way would be optically measuring the blood flow through an ear lobe or finger.

My suggestion might be particularly relevant to this project - KISS (Keep It SimpleS). So back to basics: What is the current required to drive each LED with an acceptable brightness? I hope your reference to 470k driving the LED was a typo, did you mean 470 ohms? How many LEDs will be on at the same time? What battery are you planning to use (in particular the voltage, technology and size)? Is the overall size of the device planned to be small?

Personally, I would multiplex the LEDs into a 4 x 5 matrix (or perhaps 3 x 6). That only requires 3 - 6 current-limiting resistors and 9 pins, so a 14-pin PICaxe should be sufficient. Maybe the LEDs can be driven directly from the PICaxe pins (in which case you might consider a Charlieplex, requiring only 5 pins, I think) or just 3 - 5 drive transistors (60 - 100 mA) should keep within the PICaxe totail rail current limitations. BC337s, etc. mentioned by Paul would be fine, or also any similar locally available equivalent.

Then (if there is a spare PICaxe pin or two) I'd add a tiny speaker/earphone. Sound gives very good "added value", only one pin and not much power needed, fairly easy to program and plenty of scope for creativity.

Cheers, Alan.
 
hippy

hippy

Ex-Staff (retired)
AllyCat said:
Personally, I would multiplex the LEDs into a 4 x 5 matrix (or perhaps 3 x 6) ... Maybe the LEDs can be driven directly from the PICaxe pins ...
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That would be my preference, a simple multiplex scheme with no current limiting LED's, and doing nothing fancy or over-ambitious. I think there are two key factors -

1) Shortness of time, necessitating a simple and easy to implement solution.

2) That your girlfriend probably won't be half as interested in what it does or how than that you did it. You have to balance effort put in against a potential and transitory "Wow! Love You!" and that being the end of it.

I don't mean to sound mean-spirited or cold-hearted but reality is that effort put in is not always proportionally rewarded by appreciation of that by others and there's always a point of diminishing returns. It might be better to put effort elsewhere, not put all your eggs in one basket.
 
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beatzmikee

New Member
As for batteries I got a good deal off eBay I got 100 rechargeable batteries 1.2v each 3000 mah each so I was planing on using 4 4.8v and the mah should be enough just to light up the LEDs I see what your saying hippy I just wanted it be something to remember me by :) and something like would be unique that no one else could of or would of given her :) plus something built with my hands and a lot of solder ;) lmao you guys are funny :p umm.. I have a lot of resistor values just in my experience with a capacitor and a 470k resistor (came with one of my LED packages) I had the best output was pretty bright and it stayed lit from the capacitor for like 2 hours I had it light up about 8 LEDs
What would u guys recommend as a good resistor value?
My plans are still the same for having them light up 8 LEDs at one time with each segment I <3 U
So what your saying hippy is it might not even be worth it to throw on a picaxe? I would get the same reaction even if I connected some transistors? With a button and just hook it straight up so when she presses the button it lights up..?
 
hippy

hippy

Ex-Staff (retired)
beatzmikee said:
So what your saying hippy is it might not even be worth it to throw on a picaxe? I would get the same reaction even if I connected some transistors? With a button and just hook it straight up so when she presses the button it lights up..?
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I wouldn't discount using a PICAXE but I would say it's probably not a necessity to be too clever or ambitious in what it does, as something less may indeed deliver as much appreciation for what you have done.

It's a bit like if you were buying someone a car for a present; would wrapping it in gift paper, or using the best wrapping paper you could, really add anything to it or even be noticed ? It's hard to say because some people will appreciate the extra effort but others less so.

It's really just a reminder that it's not necessarily what you are giving but how it is received that really counts.
 
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beatzmikee

New Member
ok so i know i cant hook up 8 leds to my picaxe and just have them light all of em up lol soo... how would i go about lighting all 3 segments of 8 leds three outputs from picaxe and a touch sensor :) (kind of noob here)
keeping the same plan i have about 23 leds and each letter or symbol has about 8 leds in each segment i am using a 4 battery pack with 4 rechargeable batteries 300mah each and 1.2v each i have a 100uf capacitor and 100k ohm resistors so far i was thinking about some transistors to help out with the current. any other ideas for this? i made it simple bc of time i have and the fact that if we break up she would prob just throw it away lol.. but a learning experience all the same
 
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SAborn

Senior Member
To buy you a little time the gift might be better suited to Valentine's day, that gives you an extra month or two to complete it, and a few weeks to find a Xmas gift to buy. (errr perhaps a electric toothbrush)
 
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TheChief

Senior Member
looks great on my breadboard but thats with my 28x1 and i dont want to use that..
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Don't tell her that, or it will probably be the last time you will have to go to this much trouble for her. ;)
 
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