Profezzorn's first build (graflex 2.0, teensy, prop shield, neopixel led string)

[profezzorn]

Woot! I think I found a better BEC. Assuming it works as advertised, the voltage is adjustable, the amps are equal or better (10A peak) and it's smaller than the one I'm using now.  I should be able to use it to power both the blade and the teensy, thus eliminating one of the BECs in the circuit diagram and simplifying the circuit a fair amount.

[profezzorn]

Got a pack of LEDs today:



These are 3mm LEDs, forward voltage is 3.2 to 3.8 volts @ 30mA. They are bright enough that I see yellow spots after every time I test them. :) I estimate that I'll be able to cram in about 140 of these in a blade, which will draw 4.2A, for a total of about 13.5 watts.

I'm using 20-gauge tinned copper wire for the power rails. I could probably use a more traditional bent-leg-ladder instead, but the LED legs are pretty thin and might not hold up very well to 4.5A. This handy chart sayd that 20-guage should be good up to about 11A.


Only 135 to go...

[profezzorn]

Possibly final circuit diagram:



This also includes the sdcard adapter, which can either be the pjrc wiz820+sd adapter or the standalone sd adapter. The sd card adapter is optional though. The 8Mb on the prop shield is enough for at least one sound font, as long as it's not too big.  I'm going with the plain sd card adapter, which needs to be connected with wires. The Wiz820+SD adapter can be connected directly to the teensy with pins, just like the prop shield, but the sd slot ends up at the opposite end from the usb port, which can be a problem.

One thing that I have not included is schematics for how to wire up an RGBW led star. You'd need FETs or LED drivers, and 4 PWM-capable pins on the teensy. I'm not planning to do this myself, but I don't mind helping if someone else wants to do that.

[Obi_1]

Great work profezzorn! And welcome in the club of saber electronics wizards! It is good to know that this community is growing.

If you like you can have a look into my User Manual:
https://github.com/Protonerd/DIYino/blob/master/DIYino_v1_User_Manual_draft_v03.pdf

I described an idea how to extend the battery life in spite of the power hungriness of neopixels even in idle mode. Feel free to use it if you like, Í dubbed it programmable kill key.

I recall you want to synthetize the hum sound on the processor you are using. There is a guy calle racemaniac, same name on this forum actually, he is working on a similar project, maybe you can bundle up for sharing ideas. Definitely what you are up to guys will make hum much more fun an realistic, not to mention motion effects and swings more realistic.
rgb ledstring lightsaber

[profezzorn]

Great work profezzorn! And welcome in the club of saber electronics wizards! It is good to know that this community is growing.

If you like you can have a look into my User Manual:
https://github.com/Protonerd/DIYino/blob/master/DIYino_v1_User_Manual_draft_v03.pdf

I described an idea how to extend the battery life in spite of the power hungriness of neopixels even in idle mode. Feel free to use it if you like, Í dubbed it programmable kill key.

The programmable kill key seems exactly like what I have in my circuit design above. (An N-channel FET disabling the power to the neopixels.) Does it work well to hook up the neopixels directly to the batteries? All the neopixels I've seen say to use 4.5-6 volts, so I'm driving mine with a bec, but it gets a bit hot.

I recall you want to synthetize the hum sound on the processor you are using. There is a guy calle racemaniac, same name on this forum actually, he is working on a similar project, maybe you can bundle up for sharing ideas. Definitely what you are up to guys will make hum much more fun an realistic, not to mention motion effects and swings more realistic.
rgb ledstring lightsaber

Cool, I'll be reading up. :)

[profezzorn]

Figured out how to attach the sdcard adapter to the teensy+prop shield. It requires a few wires, but it's sturdy and the sd card points in the same direction as the usb port, so they can both be made accessible though the pommel.



The eagle-eyed among you will, also see a FET attached to the other side, which means that the only external components left is a level shifter and two resistors.

[Obi_1]

The programmable kill key seems exactly like what I have in my circuit design above. (An N-channel FET disabling the power to the neopixels.) Does it work well to hook up the neopixels directly to the batteries? All the neopixels I've seen say to use 4.5-6 volts, so I'm driving mine with a bec, but it gets a bit hot.

**** I wanted to write something nasty about teh guys writing the spec for the neopixels. So far I've been using only the WS2812 style stripes, but they are fine with down to 2.5V!!! It's even detrimental to use 5-6V, because the Vth of the LEDs stay the same as for conventional LEDs, i.e. ~2V for red and ~3.6V for blue and green. You can quess what that means: if you power the LEDs with say 5V and want to have red color, you have to dissipate ~3V, that is 60% of the power! And to prove the theory I also measured it. I connected the stripe to a bench power supply, and went in both directions, while programming all red with pwm=255. Until the Vth_max (somehwre between 2V and 3V) the current resembled a diode curve, then it suddenly jumped but the LEDs did not get any brighter -> the excess voltage is wasted on clamping circuitries.
I have now a saber which connects the 3.7V 18650 battery directly to the stripes (as in the User Manual) and it works perfectly. Probably for green and blue you could go up with the brightness using max 4V, but the gain would not be that tremendous.

This also explains why yours heats up.

BTW, what is a BEC? It is like a boost DC/DC?

[profezzorn]

BEC = battery eliminator circuit, it's a buck-converter that takes a higher voltage and outputs a lower voltage, with fairly high efficiency. The term "BEC" is mostly used in the RC hobby circles, and most BECs are made for quadcopters and other RC vehicles.
(Which is advantageous for us, as quadcopter BECs are small and light.)

I'll have to do some experimentation with running my blade at 2.5-4 volts, because if it works it would certainly be a lot more efficient, but I'm not sure if the PL9823s are as forgiving as real WS2812Bs.

I've always assumed that neopixel style devices have linear regulators configured as constant current drives in them (one for each LED), but those usually drop about a volt or two. If you can drive neopixels as 2.5 volts, that either indicates that the LEDs have a very low forward voltage, or the regulators don't work the way I expect them to.

[profezzorn]

I really hope running my LEDs directly off a single LI-ION battery works well, because it makes everything better:

• There will be more space in the hilt
• Less energy will be wasted as heat
• Total battery Wh goes up
• Battery life nearly doubles (at least if you use 3200mAh batteries)
• Fewer external components (no need for a voltage divider to measure battery voltage anymore.)
• Fewer used wires to the blade means RGB stars/strings become possible.
• Much less energy wasted in resistors when driving non-neopixel blades

[profezzorn]

Hmm, my PL9823 don't loose a lot brigtness if I power then with 3.7v, but brightness drops pretty much linear from there down to about 2.5v. Now I just have to decide if I want 15 minutes of 100% brightness or 30 minutes of 95% to 30% brightness. I tested with blue, because PL9823 defaults to blue, and it's actually the color I care most about.

[profezzorn]

Hmm, looking at panasonic discharge curves, it seems that the battery will stay above 3.3v for the majority of the discharge time, and then start dropping quicker and quicker at the end. At 3.3v, the blade still has *most* of it's brightness, so maybe I should think of it as 20 minutes of 80% brightness or more.

Now I just need to find out if running the blade at less voltage lets me get rid of the level converter, because that would be *sweet*.

[profezzorn]

Answer: No, I can't get by without a level shifter.
In fact: The PL9823 LEDs don't are not particularly stable at 3.5 volts, even *with* a level shifter.
(At 4.1 volts they behave much better.)

So, I guess that pretty much settles it, I'm going to keep using my BEC.

[profezzorn]

The BEC I have can be programmed to change the voltage. It's too bad that the lowest voltage I can specify is 4.8 volts. If it could go lower, it could directly drive LEDs, which would be an awesome feature.

[profezzorn]

I've been working on a chassis for my saber:



It's going to be a pain to print on an FDM printer (which is what I have). I might have to build supports into the design.

[Obi_1]

Answer: No, I can't get by without a level shifter.
In fact: The PL9823 LEDs don't are not particularly stable at 3.5 volts, even *with* a level shifter.
(At 4.1 volts they behave much better.)

So, I guess that pretty much settles it, I'm going to keep using my BEC.

I'm just curious what you use as a level shifter and if it has enough current capability to fully supply the LEDs. Unfortunately the PL9823 datasheet is very basic, it does not even have a proper electrical parameters table. I looked up that of the WS2812B, it says the LEDs have 2-2.2V (red) and 3.4V (green/blue) max voltage, so any voltage above 3.4V is wasted. But I will do a shmoo with my LED stripe to see at using which color where the clamp begins and where do I see a sudden increase in current.

But I saw one strange drawing the datasheet for the PL, it has a limiting resistor drawn, this could maybe explain the difference, maybe the PL has a passive current limiting while the WS does it with active components.