Monday, January 2, 2017

Taken by a Strange Mood, Part 4

What do you do when you've permanently affixed a loud fan to your new homemade smartTV?  How do you quiet it down?  How about with lower fan speeds thanks to the new software PWM module in RPi.GPIO for python.

Do what now?

So we have all these extra pins on the Raspberry Pi. These pins are known as GPIO or "General Input Output Pins".  We can do some cool things with these pins in software.  One of the things we can do is, with a python script, control whether a pin is a sensor for 3.3v, or if we're sending a signal of 3.3v on each pin.  There's also another cool thing you can do, and that is send a variable voltage across a pin through a neat little trick called Pulse Width Modulation (PWM).  PWM emulates a variable voltage by pulsing the maximum voltage (3.3v in this case) at a high frequency.  In theory this will allow me to control my fan speed through code.

I say in theory though, because what I have is a 5 volt fan, and the GPIO pins only output 3.3 volts.  I tried hooking up the fan to the GPIO pins directly, but 3.3v apparently isn't enough to get the fan spinning.  It NEEDS a 5 volt pulse to go.

Well, now what am I supposed to do?  I can't control the fan directly because I can't pulse a high enough voltage to get it to spin up.  And I can't control the 5v pin, because its connected directly to power.  I can't interface with it through python code.  Enter the Transistor.

How transistors work is beyond my knowledge.  All I know is how to wire one up to do what I needed it to do. Basically, when wired properly, a transistor works kind of like a relay switch.  It has 3 pins, a base, a collector, and an emitter.  When a voltage is applied to the base, it connects the collector pin and emitter pins.  When the emitter is ground, and the collector is my fan in series with its 5 volt supply, it acts as a switch that I can control with a 3.3 volt pin.

Back to the internet!  I ordered a pack of PN2222 transistors, some 5050 LED breakout PCBs, and some assorted wire for me to solder to.  I followed along with this tutorial in order to figure out what needed connecting where.  After some fine wire work, soldering and clipping of legs, we have my finished transistor module:

All that remained was putting it into the case. Unfortunately I don't have any pictures of what it looks like in the case.  I'll be diving in later to make another modification later this week, so I'll try to get a picture then.  Suffice to say, it's become a bit of a mess.  BUT, I have the ability to control my fan speed programmatically through python.  BEHOLD MY CODE!

Sorry for the pictures.  If you need to copy it for your project I have it here.  There are a couple of extra lines of code in there for the next phase of this project, which I will detail in part 5.

So a basic explanation is that we import the modules we need at the top, followed by initializing some constants like what pin is connected where, how much I want the fan speed to step up or down as a percentage (that's your duty cycle, percent of time the pulse is on vs off).  Then we define a few functions to get the temperature in a usable format, write temperature and fan speed to a file, and then run the meat of the code in a loop.  Every cycle, we check the temperature.  If its above my set max temperature, we'll increase the duty cycle by the "step" amount.  If its below the minimum temp we decrease the duty cycle.  This arrangement allows the temperature to sit between the low and high level with the slowest fan speed possible, minimizing fan noise.  Then we wait (sleep) for a period of time and do the check again.  I can tell you, after having run this for a number of days now, it works great, and its very slick.

In part 5, we'll talk about what happens when you hit the off button, and what SHOULD happen, and how we make what SHOULD happen actually happen.  Seeya later.

Taken by a Strange Mood, Part 3

As I intimated at the end of Part 2, there were problems that extended this project.  Sure, I had a working embedded Plex image running on the Pi, but I had more ambition for that.  I downloaded and burnt the latest RetroPie image to an SD card and got that started.  The original plan was to have 2 SD cards: one for games and emulation, the other for movie watching.  Then I found out that Kodi could be installed under retropie, and that there was a brand new Plex plugin for it.  Once I discovered that, I stopped using the Plex image altogether, and have stuck with retropie.

This is not a blog post about setting up retropie, however.  It went pretty standard as long as you follow along with their instructions on their page, so I won't address that.

No, the problem I started seeing almost immediately is app crashes, freezing, and unexpected behavior.  The IC on the Raspberry Pi 3 is rated at a max temperature of 80' C.  When I checked my temperature, even at idle, I was running mid 70s.  Yipes.  Too hot!

Even though the RPi shouldn't need active cooling under normal circumstances, I was not operating under normal circumstances.  Ambient temperature inside the TV was affected by the TV electronics heating up, so the pi could not passively cool effectively.  I needed a fan.  At 5V, 0.2A max, this fan seemed ideal.  So I bought it.  It can plug directly into the 5V rail of the GPIO on the pi, and connect to ground. There are 2 pins on the GPIO that seem like they were designed for just this, pin 4 and 6.  All we need to do now is open up my case, and install the fan.  Sounds easy, right.  Well it would have been easy, except that I had ALREADY permanently affixed the thing inside my TV, so I couldn't remove it to get the top of the case off, or do anything else much with it.

Fortunately, the case didn't snap closed, and there was just enough wiggle room for me to be able to fit the small fan into the gap I could create between the top and bottom of the case.  Here's the other problem: no vents in the case.  Time to get out my drill!
I picked the closest sized coring tool I had in my drill bit set, lined it up, and went to work.  Even at slow speeds the drill didn't so much cut through the plastic as it melted through.  My plastic chips were all melted together, and some of them are still stuck inside the case.  Now came the hard part, getting the fan in there, and also mounting it to the inside of the top half of the case.

Case with fan hole cut.
I ended up using two small allen wrenches as feelers to position the fan under the hole.  Got another JB weld mix going, and then tried to hold it in place for 15 minutes. That didn't happen.  I was shifting the fan all around as I tried to hold it steady.  I needed a more permanent temporary way to hold the fan in place while I waited for the epoxy to cure.  In came my good old friend, Masking Tape.
Pull up, apply masking tape, hope it doesn't fall

Now that I had the fan in place, I needed to do something about the metal plate that covered the Pi here.  You see, a fan doesn't do you very much good if it doesn't have any access to ambient air to blow.  I sized up the location of my fan relative to the edges, and laid out my new hole pattern I was going to drill.

Hole Pattern

Drilled holes.

Holes in plastic cover
I think I messed up the label.

By the time I was finished drilling holes, my JB weld finished setting, and it was time to bring it all together. I plugged in the fan into the two pins I mentioned before  Closed the whole thing up, and turned it on.  Fan spun up.  It sounded like the blades were brushing something, because it was loud, and getting louder.  Even completely covered up by the case, running at 10k and brushing something with each blade on every revolution, this thing sounded like a small dustbuster.  This was No Good for a media smart TV.  I opened the thing up again to see if I could find what we were running into.  Turns out that this particular fan doesn't keep its wires away from the fan blades very well, and the blades were brushing the wires.  This took lots of finagling over several attempts to get the fan where it wasn't hitting itself when it spun up.  But even then the sound was very loud.

I checked my temps, and this thing was running cool.  I want to say it was less than 55' C under full load with the fan fully spun up.  So it was doing its job, just at a audible level I was not happy with.  Remember how I used JB weld again, and this thing was now a permanent resident?  Yeah, time for some more engineering.

I almost forgot to mention.  Before all of this I was getting a lot of noise out of my speakers.  Anytime something would be busy on screen, or there was disk activity, I'd hear a little noise.  Turns out the AV cable I used wasn't of the highest quality, and in addition the way I had my power supply connected meant that my Pi wasn't getting properly grounded.  I fixed that (mostly) by adding a wire from a ground GPIO pin to the case.  No, that solder joint didn't hold, but the wire is sandwiched between the side plate and the top plate, so it stays in place.  And my noise was reduced significantly (but not totally).  Too bad that AV cable was now a permanent resident.

In part 4, you get to find out how I dealt with my obnoxiously loud fan.

Sunday, January 1, 2017

Taken by a Strange Mood, Part 2

I forgot to mention one major minor detail from my parts build.  You see, the Raspberry Pi 3 has build in WiFi and Bluetooth.  That's good.  The bad news is that the whole assembly will be trapped inside the metal chassis of my TV.  Not very good for wireless signals.  Fortunately, there is an external antenna mod you can do on the Pi, with questionable legal ramifications (since you're messing with an FCC approved device, and thus potentially voiding the Pi's certification).  I followed along with the guide here.  I ordered the antenna parts. I was going to attempt to solder on a U.FL connector to the bottom of the Pi, but when I got the parts in hand I determined that the connector was WAY too small for my shaky hands and giant soldering iron.
Doesn't look so bad on the guide.

Oh wait, that spot is smaller than a fingernail.

The solder point for U.FL is those two copper pads.  You also need to move a Zero Ohm resistor, which is about the width of 5 hairs.  How about Nope!

So I went with plan A on the guide: top mount.  I broke off my Pi's ceramic antenna and soldered on the lead for my coaxial antenna.  This was a major ordeal, since my solder did not want to stick to either the ground plate, and I had to resolder the thing at least 3 times before a had a solid strong connection.

Ok, now that we have that detail out of the way here are the parts before assembly:

And here's how they're going to look placed in the TV chassis:

Parts arrangement, so ensure everything would fit.
Original (removed) plug on left

I originally planned to have the SD card ribbon sit just above the USB ports on the Pi.  Unfortunately, once the added space of the plastic case was added, there was no room at all for this configuration.  I ended up moving it above the Pi (in the direction of the top of the TV).  Before I did any cutting, however, I needed to make sure that my 12V to 5V would provide enough consistent power to operate the Pi off of.  The 12V connection come on at TV power on.  I went ahead and made my power adapter connector, and modified the cable to have the correct sized USB plug on the end.
Soldered leads together.

Wire with electrical tape.

So, that took care of the business end of the 5V downverter.  I enlisted the help of my lovely wife Nancy to ensure that the Pi would indeed boot when all the parts were connected together.

Holding the leads to the power supply!

You can barely make it out, but the red LED on the pi is lit.  Our power supply works!

The first cut spot.
With my power connection verified, I felt now was the time to start cutting.  I marked where I thought the SD card ribbon cable would come out with red dry erase marker and got out my dremel. "But Specter," you say, "What about all the metal shavings!  Won't they get all over the motherboard and cause all sorts of shorts and damage?!?!"  Why yes.
Dust "Collector"
But I have this brilliant plan!  I'll stick a big rare earth magnet on the other side of the chassis inside a plastic bag, and it will collect all the metal dust for me!  What could POSSIBLY go wrong?  Did I mention that I was in a strange mood.

Long story short, don't do this.  Ever.  While I was able to collect a lot of the metal dust the dremel produced, it was impossible to collect ALL of it, and there was a fine coat of dust all over the sensitive electronic components.  I got as much up with the magnet as possible, but then I had to get a damp rag out and literally dust every surface I could reach.

And now.... the first incision.

I didn't destroy the project with this boneheaded move, luckily.  But for every subsequent cut, I took the bracket off the chassis, took it outside, and did my cutting there.  And boy am I glad I did.  This was 1/16" thick STEEL.  It took a relatively long time to do all the cuts, and then buff out the burrs and do fine trim ensuring consistent sizing.

While I had the plate off, I went ahead and drilled a hole for my external antenna, down near the existing coaxial "antenna" spot.  Here's how it all looked after all the steel cutting and parts approximately in their final places.

New Window
Components in place
JB Welded.  And proper plug placements
You can see in the above picture that the clear plastic case has no venting to speak of over the CPU (which has a heat sink).  This will come up in part 3 of this series.  Now, the only thing left to do was JB weld it all together.  The container claimed that the compound would take 15 minutes to set, and 30 to be at a machinable cure.  Perhaps I got a bad mix, but it took at least 30 minutes for it to set for me.

Anyway, I got it to set, and got all my piece parts in place where I wanted them.  The power supply cable fit nicely in the crevice between the TV PSU and the TV motherboard.  I was able to snake it up and around to the pi plug without it getting in the way of anything.  The SD card ribbon wrapped up with a rubber band.  The AV cable JUST fit between the SD card port block and the pi itself.  But this cable is now permanent.  The plastic case is welded to the chassis, as is the SD card port, and there's no room now to remove the plug from the pi.  I sure hope that I don't regret going with AV for my video.  Time to close it up.

That dust was from the dremeling before.  Yuck.

The final plan is going to be to wall mount this TV in my kid's playroom in 6 months or so.  I'm a little bit concerned that the meat I took out of the side plate might have compromised the strength of the VESA mount plate that attaches to it.  Here's hoping it doesn't fall off the mount.  I'll let you know if it does.  Only thing left is to plug it in, turn it on, and see if it works.

It Works!  Plex image from Part 1 running clearly!
I wish I could say that this is the end of the tale.  That this ended here, with no further problems, and that this mod only took me 2 days to do, instead of 3 weeks.  But I can't.  There will be a part 3 of this series. Perhaps even a part 4 and 5.  But though the struggle was long and epic, the results are awesome.

Taken by a Strange Mood, Part 1

About two or three weeks ago I was taken by a strange mood.  We had our annual Christmas party, and I decided "wouldn't it be great if I could have movies in the back of the house as well as in the front."

Westinghouse 32" TV.  Collecting Dust.
We have this old 32 inch, 1366x768 Westinghouse LCD TV.  It used to be our primary TV (and was our very first flat panel HD television).  It doesn't even have HDMI ports, it's that old.  It served us well in its prime, but it has since been replaced by a 47" LCD (which was struck by lightning) which was replaced by a 55" Sony Bravia (the old version that weighs like 80 lbs and is 6 inches thick).  When we got the Sony, the Westinghouse became the bedroom TV, where it served admirably until about 2 years ago, when I wanted a chromecast for the bedroom.  Since it didn't have HDMI ports, I ended up buying another TV (42" RCA, I think), and so the old reliable Westinghouse was put in a back room to someday be used for something, probably.  I got my spare Raspberry Pi out, connected it to the TV's DVI out, with RCA audio, and burnt an embedded PLEX image to a spare SD card.  It booted, but the PLEX image did not know how to handle 1366x768 properly. Christmas party TV was a bust.  But there would be other parties.

Then, I got a brilliant idea!  Why don't I use a raspberry pi to turn it into a smart TV.  And not just a smart TV, but a retro game playing, plex movie watching smart TV.  It might work.  It could work.  And after I checked out the back of the thing, I might even be able to mount the Pi INSIDE the TV.  MWAHAHAHAHAHAHA!  Did I mention it was a strange mood?  I wonder if other engineers get these.

I took my existing RPi that I use for my backup server out of its case and opened up the TV, just to size it up.

Low and behold, not only was there space for the Pi to sit, but it looks like there was an entire area of this particular TV PCB that was unused (probably for a model with more features).  Now that I look at the pinouts in this area, it looks like it might have been a SCART input, or something similar.  You know, one of those TV connections that nobody knows about unless they work in media and television.  This is where I checked to see if the pi would fit.  Spoiler warning.  It did.  The next thing I needed to do to make this viable was find me a 5V power source inside the TV that I could power my raspberry pi off of.  I checked numerous plugs and connectors, and found several 5V spots.  Problem was, evertime I checked across them, the TV would shut down after a moment.  These were no good.  I then took a look at the power supply, and what to my wondering eyes appeared, but an unused, 4 pin connector.  I got my voltmeter out and read across the pins.  Two of them were ground.  Two of them were 12V.  But they didn't cause a TV shutdown when I read across them.  If I could just get a voltage downverter, I could connect here.  If only there was something you could buy that took a 12V input, and output 5V for charging a cell phone... like... a car charger... TO THE INTERNET!!!!!

The strange mood was in full swing now.  I was powerless to resist this new mania.  I found the perfect device here. Only problem was it had the wrong kind of USB plug on one end.  No matter.  I have a soldering iron and spare micro-usb cables all over the place.  The other problem was I had no idea what kind of plug that was.  Fortunately, the nice folks at the Adafruit forums came to the rescue.  I got on the amazon and ordered this, a Raspberry Pi 3, along with a clear plastic case.  The USB and Ethernet ports would face out of the TV chassis just below the AV1 input.  The trouble with this is that the micro-sd card is in the opposite side of the pi, and would be facing the inside of the TV chassis, completely inaccessible without opening the TV up.  I really didn't want to open the TV every time I wanted to try a new Pi image.  I wonder if they make Micro-SD Card Ribbon Cables?  They do.

Two questions remained.  How did I want to hook up the AV from the pi, and how was I going to get it all to stick firmly inside the TV chassis.  After much deliberation, and the bad DVI experience I had before, I decided to just use the Pi's AV out and connect to the AV1 input on the TV.  I kicked around the idea of wiring it directly, but ultimately decided to just use a cable, run it outside of the chassis, and into the inputs on the outside.  This would allow me unplug if I ever wanted to use the AV port for something else in the future.

As for how I would stick it all in there without worry, I decided to go with JB-Weld epoxy.  I may ultimately regret going with such a permanent solution, and it did make a few future mods more difficult.  But I won't have to worry about this stuff falling out of the TV ever.  And I mean EVER.  Next time, I'll show you how it all came together.