Author Topic: Sloppy, but useful recycling and repurposing at it's finest :P  (Read 885 times)

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Offline MadScientist267

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I've mentioned the fact that there's a "webapp" (only actually accessible locally) to view, monitor, and control the various aspects of the truck project that are run by a raspberry pi.

There's a tablet that's mounted on the rear wall that's dedicated to this purpose, but it's essentially permanently attached. I can use my phone to do the exact same thing, but have to disconnect from the web to do so, which is a pain when it comes to certain things, IRC being a notable example. I have a larger tablet that is mostly for watching locally stored video during times that power is precious, but due to how things are laid out, there's a similar issue to the phone, as the video is stored on a completely separate device that doesn't readily play nice with the main network.

Certain functions require babysitting by design, one in particular - the dead man switch for the power hungry TV. Sleep mode, while present in the TV, isn't the ideal way for a couple of reasons to deal with nodding off while it's on. Mainly because there's no absolute insurance that I've engaged it. Other things that are inaccessible (particularly from the "winter bed") are things like the thermal management pages and the like. Or maybe I just want to pick and play some tunes on the fly (also done with a pi).

Ok so those are the problems. The solution?

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Well, a retired phone, right?

Hmmmm... Well that's great on paper except this one had it's battery nearly go Chernobyl by sitting on constant float for months on end and in some extreme temps while it served as the original media playback device.

I removed the ballooned battery upon it's discovery, and replaced the media functions with the aforementioned raspberry pi pretty much immediately (priorities, man!)... and chucked the phone in the parts bin for later revival.

What I didn't understand at the time was that even tho the original battery appeared to be just an "unpackaged" prismatic cell (it's technically not replaceable) attached by a printed ribbon cable, the devil was in the details, as there was a hidden BMS board buried in the battery despite the appearance that it was within the phone instead.

Not willing to dump any cash into the project, I had another essentially brand new battery (originally for the cheap standalone media streaming device I got from wally world and ended up having to heavily modify). It wasn't incredibly difficult to get it connected to the battery terminals on the phone, but as I had just left the torn off ribbon for later removal, I missed out on this useful heads up. (It actually ripped free when the adhesive holding the battery in the phone let go, so some of this is moot but included for completeness).

Under the screw terminals, low and behold, were the contacts for the BMS communication. I figured there might be issues with what it expected to find (in terms of raw capacity), but [ignorantly] thought that it would still pretty much function at a basic level. Bzzzzt.

It worked, and would boot the phone... but this is what it thought of my new arrangement for it...

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Something similar appears in the notification bar icon when the phone is on (the above only appearing when attempting to charge it while it's turned off). It refuses to charge the surrogate in any way, shape, or form. In hindsight this makes perfect sense, as since it can't determine the battery's state (SoC, overdischarge lockout, etc), it can't just assume that it's safe to charge based on voltage alone.

Ok so now what...?

I ran it long enough a few times to get it set up to do remote control duty, and then once again shelved it for lack of an immediate solution.

Tonight, the need for a dedicated remote finally got the best of me and I set out to take it on. The end solution is surprisingly simple, just had to simmer on the back burner for a bit I guess LOL...

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I scrounged around for what I had immediately on hand, and came up with this. It's a male DB9 (RS232 etc) connector, using 2 diodes to connect each leg from the phone's battery connection to the DB9. They're not visible, inside the sheathing that is simply some stripped insulation in lieu of heatshrink... It's another story entirely as to why I found myself suddenly without any... LOL.

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The diodes provide a super simple means to get sufficient voltage drop to be able to charge the battery from a 5V source. The only other components that were added are a 1/4W 10R resistor (actually on the charging adapter rather than part of the assembly on the phone for simplicity purposes). It just ensures that currents always stay low in the event that it's allowed to discharge down to where the battery's BMS does a safety disconnect, a little bit less than 3V. It's an 1800mAh cell, and while I'm sure it could handle pretty much any inrush that might flow, those are 1A diodes (1N4002) and it just made sense. It doesn't need to charge fast, it will be connected to the charger something on the order of >95% of the time.

The battery should slowly float up to about 4.0V or so when left for extended periods on the charger with the phone turned off, plenty of safety margin for the top end. It's also below the level where the electrolyte would begin to vaporize, avoiding the whole puffy battery thing from the gitgo, among a couple other advantages.

This does come at the cost of reduced capacity, but this isn't critical, as it serves no other purpose and as mentioned, is likely to spend most of it's remaining life connected to the charger when it's not actively being used.

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The other component is just an amber LED to indicate the charger is connected and providing juice.

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It doesn't really comply with the Razr's theme of being uber thin, and it's presently attached with a little bit of gorilla tape until I'm ready to make everything neater and finalize it, but it works and that's all that matters ;)

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Here it is pictured with the modified (but genuine! LOL) Verizon charger... For once, one of these insanely useful and adaptable little buck converters is doing something that closely resembles it's original purpose ;D

There's one other fringe benefit... in an emergency, 911 is theoretically always on tap, in the event that for whatever reason, I can't use my phone-phone. ;)

That's all for now... I know this is long winded for what it is, but represents something that will make my life easier... Something that seems to be on short supply as this whole thing has gone into full swing. :o

Steve
Wanted: Schrödinger's cat, dead and alive.