Arduino and LED Matrix in a car?

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Vitamin K
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Arduino and LED Matrix in a car?

Post by Vitamin K » Tue May 24, 2016 9:05 am

So...next year is the boy's last Pinewood Derby as a scout, and I'm thinking I want to encourage him to build something...different.

Now...we were kicking around ideas for lights...which is still a possibility, but the other day I opened up the Arduino starter kit I had received a while back and found the 8x8 LED display that it included. And I started wondering.

Google quickly revealed that this has, indeed, been done. https://blog.adafruit.com/2014/03/17/le ... o-arduino/

What I wanna know is...can we do this, and still make the car fast?

An Arduino micro weighs about 13g. I think we can work with that. The LED display comes in at 2.9 grams. Then there's some wires and two shift registers. All manageable. My main concern is the power source. The link above is using a 9 volt battery, which is pretty hefty. Wondering if I could get away with wiring some button cells in series to get the appropriate input voltages?

Help me out, electronics wizards! ;)
Last edited by Vitamin K on Mon May 30, 2016 8:54 pm, edited 1 time in total.



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Re: Ardunio and LED Matrix in a car?

Post by Vitamin K » Tue May 24, 2016 9:32 am

So it turns out, ADAfruit sells this LED display with an I2C "backpack" that vastly simplifies the amount of wiring required to control the Matrix. I think the less wiring required for fitting components into a car, the better!



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Re: Ardunio and LED Matrix in a car?

Post by bracketracer » Wed May 25, 2016 11:11 pm

Maybe rather than a big 9v, try one of these miniature 12v batteries?:

http://www.energizer.com/specialty-batt ... 23-battery



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Re: Ardunio and LED Matrix in a car?

Post by Vitamin K » Thu May 26, 2016 5:50 am

bracketracer wrote:Maybe rather than a big 9v, try one of these miniature 12v batteries?:

http://www.energizer.com/specialty-batt ... 23-battery
Thanks for the suggestion!

Looking at the specs for the A23s, it looks like they have a capacity of about 55mAh and weigh ~8 grams.

I think a better choice might be to wire three CR2032 batteries in series, which would give me an output of 9V. The CR2032s have a capacity of 225mAh and weigh about 2.3 grams each, so a total weight of ~7 grams.

Another thing that I think we'll try to do is to install an accelerometer, and poll for input from that to determine whether or not to activate the LED matrix. Not only will this (hopefully) help with battery life (since it'll only light up when the car is actually moving), but it might be able to let us make the graphics context sensitive, if we can figure out how to determine whether the car is just picked up by a stager, or if it's actually moving down the track.

I think what I'm going to do first is to order the matrix and just wire it up on the breadboard with the accelerometer (I already have one, from this Arduino starter kit I got) and the Arduino, and then put my multimeter on the power source to see what the current draw is when the the matrix is displaying something, versus when it is just sitting idle and listening to the accelerometer for input. Once I know that, I think I'll have a better idea of what the power requirements are going to need to be.



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Re: Ardunio and LED Matrix in a car?

Post by whodathunkit » Fri May 27, 2016 11:25 am

Vitamin K,
Looks to be a fun project car.

Best of luck with the build hope you'll post some build photos!




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Re: Arduino and LED Matrix in a car?

Post by davet » Mon Jun 06, 2016 7:04 am

At our Council race recently there was a car with 8 LED's blinking rapidly in random order. It was the coolest lighted car I've ever seen. He used 8 LED's from a hobby store that were intended for model trains. Each LED blinked on it's own. He operated it with a micro switch that he could turn on and off. Powered by small watch battery, not sure what size.

We used 4 LED's powered by a CR2012 battery and they stay lit for a week. We tape the battery into the car when getting ready for the race. If you checkin the night before the race they will still be at full power the next day.

I understand those kits your looking at may take more power but really cool blinking lights may be done with less weight if you don't use the controller.
http://data.energizer.com/PDFs/cr2012.pdf



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Re: Arduino and LED Matrix in a car?

Post by Vitamin K » Mon Jun 06, 2016 12:50 pm

davet wrote:At our Council race recently there was a car with 8 LED's blinking rapidly in random order. It was the coolest lighted car I've ever seen. He used 8 LED's from a hobby store that were intended for model trains. Each LED blinked on it's own. He operated it with a micro switch that he could turn on and off. Powered by small watch battery, not sure what size.

We used 4 LED's powered by a CR2012 battery and they stay lit for a week. We tape the battery into the car when getting ready for the race. If you checkin the night before the race they will still be at full power the next day.

I understand those kits your looking at may take more power but really cool blinking lights may be done with less weight if you don't use the controller.
http://data.energizer.com/PDFs/cr2012.pdf
Unfortunately, I showed my son a demo of the Matrix scrolling the words "Turbo Mode: Engaged" so I think we are kind of stuck on needing the microcontroller at this point. :mrgreen:

Placement is going to be a challenge. The microcontroller (Arduino Nano), the Matrix w/ i2c backpack, the accelerometer and two 2032 cells weigh about 0.75 ounces together. The trick will be arranging this stuff so that the majority is towards the rear. Hoping we can still hit a reasonable COM with all the gear installed.



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Re: Arduino and LED Matrix in a car?

Post by davet » Mon Jun 06, 2016 12:59 pm

Whatever he likes best is the absolute best way to go, ideal COM or not. Very cool.



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Re: Arduino and LED Matrix in a car?

Post by Vitamin K » Wed Oct 12, 2016 7:34 am

Derby season creeps closer, so I decided to go ahead and do some testing on the electronics. Got the display and the controller wired up to the breadboard and put my multimeter onto the LED matrix to see what the current load is. With 50% of the LEDs active, it draws about 160 mA. Since a cr2032 is (typically) rated at 200 mAh, that's a little over an hour running continuously. That's at 5V going to the matrix. If I put it on the 3.3V pole instead, the current draw drops to about 95 mA, but the display is less bright. Ideally I think I'd rather the display be as bright as possible.

Next step is to wire up the accelerometer and see how much current it draws in "idle" state.



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Re: Arduino and LED Matrix in a car?

Post by davet » Wed Oct 12, 2016 8:37 am

You know the drill VK....pics. I'm not sure what one guy was running last year at Council but the entire top surface of car had around 15 randomly blinking lights. Very bright and one of the coolest cars I'd ever seen.

We found a way on our car to make the bulbs "appear" larger. We drilled the hole for the LED to fit tight and the head to be flush with the body surface. We then beveled the edge around the hole which made the hole look bigger. We then used white paint on the beveled edge. When the blue lights came on it lit the white paint blue and made the bulb look bigger.



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Re: Arduino and LED Matrix in a car?

Post by Vitamin K » Wed Oct 12, 2016 11:05 pm

davet wrote:You know the drill VK....pics.
Well, the electronics are just a mess of components and wires and breadboard right now...

Here's a possible layout of the components, relative to the car chassis...

Image



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Re: Arduino and LED Matrix in a car?

Post by davet » Fri Oct 14, 2016 2:22 pm

Very cool. How do you hook up the batts?



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Re: Arduino and LED Matrix in a car?

Post by Vitamin K » Fri Oct 14, 2016 2:44 pm

davet wrote:Very cool. How do you hook up the batts?
Well, I've got to get the cells wired in series first. Not sure if I can solder tabs onto them, or perhaps a conductive glue would be better. Need to research that a bit. I forsee just attaching leads to the cells and feeding them out to the Arduino from there. So they'll be perma-welded together into a "battery block" prior to installation.

I've added the accelerometer to the mix. When the Arduino is just polling for input and not actually lighting the LEDs, it draws about 25 mA of current. If I can figure on 150 mAh from the batteries (the specs say 200-225, but I'm being conservative), I can plan on 6 hours of continuous use (since there will probably be less than 5 minutes of the car lighting up in its "active" state, since it'll only do that when handled). Should be more than adequate to get us through our Pack Derby. If we make the cut for Districts, I'll switch out the batteries.

Next step, I think, will be to build a "dummy" car that we can just attach the components too and roll down a board to see if the motion triggers the accelerometer. Ideally, I'd like to have two levels of sensitivity: When the car is moved (e.g. picked up for staging) and when the car actually starts moving fast down the track.

We shall see... :)



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Re: Arduino and LED Matrix in a car?

Post by Vitamin K » Mon Jan 30, 2017 1:56 pm

Well, we had to delay this car. As we ran up towards race day, we just had too many setbacks and too many problems that needed solving for me to be comfortable that we could end up with something working in the end.

So...we shelved the Arduino car for the Pack derby and build a speedy "plank" car instead. We did qualify for Districts in April, so our plan is to regroup and try to get this car built for the District race, after we've completed my son's AoL requirements.



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