LED Sash (Therm/Humid/Lux/Compass/Noise sensors)

I'd like to make a sash with an Arrow design on it, with a horizontal bar above and below the arrow. The shaft of the arrow is two columns of 15 LEDs: one column lights up like a thermometer, the other column is a VU meter very similar to the one in this tie. In the top bar there is a matrix of 11 wide by 3 tall LEDs that will display humidity levels. The fletchings on the arrow are two identical/symmetrical slanted matrices 3 wide by 9 tall LEDs that light up in rows and they display light level information. Within the arrowhead there is microphone for the VU meter, a light sensor for the fletchings. At the bottom of the sash, on the lowest corner (lower left) there is a temperature/humidity sensor; on the other bottom corner there is a button power switch. The bottom bar could be a pouch to hold a battery, and/or I could mount some LEDs to it that are either lit always, randomly, or in a pattern so that it would be just as visible as the top bar.

Is it feasible to make something small/light enough to wear as a sash out of such a hodge-podge of sensors and LEDs?

I am not really familiar with basic electronics (calculating voltage, which parts to use, etc.) but I can do a bit of programming and I'm willing to learn. What I want to know is what kind of battery I would need to power all of this, and what would be the best way to efficiently use microcontrollers (multiple circuits, multiplexing, etc.).

Thank you for your time!

Sorry for the newbie question, I don't know much about general electronics.

Can someone teach me how to find the power draw for these, and by extension what kind of battery I would need? Or, at least, point me in the right direction?

After some more research, I found this post back in the 2005-2010 forum archives. Based on that, I believe that in order to find the correct specs of the battery needed, I would need to do the following:

  1. Find total amp draw (make sure to check 3.3v or 5v)
  2. Battery must be able to output at least that many amps and must output at least as many volts as the highest-voltage component (usually 5v in this case)
  3. To calculate total battery life, divide the number of amp-hours in the battery by the number of amps used in order to find the battery life (in hours)

Correct me if I'm wrong?

Calculate the amp draw on the LEDs you plan to use. Most LEDs have a draw of 20mA. I say most because you can get some that draw as little as 2mA. But let's assume that you'll go with the average 20mA LED.

Starting at the top bar, you have three rows of 11 LEDs. IF you light all of them up, that's 33 x 20mA = 660mA The fletchings are two matrices of 3x9 LEDs. Again, IF you light them all up, that's 27 x 20mA = 540mA - both sides that's 1080mA. The shaft is a comprised of two rows of 15 LEDs. All on, that's 30 x 20mA = 600mA Plus one LED at the tip, that's another 20mA.

Put them all together and you have: 660 + 1080 + 600 + 20 = 2300mA = 2.3Amps just for all of the LEDs to be on all at once. Now, keep in mind that these calculations are based on all the LEDs being on at the same time at full 100% duty cycle. Based on your description, they won't all be on at the same time, so the total draw will be lower and dependent on how many are on. However, it's always a good idea to figure out what the max draw could be.

On top of that 2.3A, you need to add the draw of the various sensors and micro controller. For the sensors, read their specific datasheets. It'll tell you their max draw.

A standard AA battery can provide somewhere between 1.8 to 2.2Ah, so if you have four of them in series (for 6V), you can drive all of those LEDs together for just under one hour. Again, [u]if they're all on at the same time at full 100% duty cycle.[/u] You could also get a LiPo battery and drive them that way.

So, answering your question of whether this is feasible? Sure. However, will it be light enough to wear as a sash so it doesn't sag out of shape, that remains to be seen. What kind of LEDs were you thinking of using? What kind of sensors, and how heavy are they? What material is the sash made of, obviously a silk sash won't hold its shape. You need to think of how the shash will change once you start adding all the wires needed to drive those LEDs. Likely also several shift registers to drive that many LEDs. Or you can look for LED strips. What are the dimensions on the sash anyway??

It may be worth looking into getting some custom boards made, the top one containing the three sensors in one board and the bottom one containing the remaining sensors and a micro controller (instead of using a Flora.)

I've done several wearable projects with custom made boards and LEDs. It's easier than you think, once you figure out your limitations.

KirAsh4: Calculate the amp draw on the LEDs you plan to use. Most LEDs have a draw of 20mA. I say most because you can get some that draw as little as 2mA. But let's assume that you'll go with the average 20mA LED. -snip so my post isn't really long- I've done several wearable projects with custom made boards and LEDs. It's easier than you think, once you figure out your limitations.

Dear sir/madam: thank you, your post was invaluable to me.

Also, I guess I wasn't clear in my original post; I meant that it was inspired by FLORA, not that I would use one to drive it (I don't think a FLORA really has enough power for much more than very simple projects). I planned on just going with standalone microcontroller(s), since they would probably be easier to secure to the sash, and smaller/lighter. For the sash, I planned on triple-layering some thick black canvas (2 outer layers for aesthetics and one middle layer to attach all electronics). Off the top of my head, I think that would be sturdy enough to prevent too much sagging.

I don't have time right this moment, but I'll go through and find the total amp draw for all the sensors and microcontrollers as soon as convenient and report back here with my findings.

It’s sir.

Don’t dismiss the FLORA so fast. After all, it is a regular 32U4, which is what the Leonardo uses. You CAN use the FLORA to do everything you’re talking of, it’ll just be a big bunch of wires tied together on the minimal pads that it has. Building a custom board allows you to break out all of the pins and you can use them any which way you want. The FLORA board is more powerful than you may believe it is.

Personally, I would recommend using controllable LED strips for the various bits and pieces, less wires to deal with compared to individual LEDs wired separately to shift registers.