Sunday, March 30, 2014

Oooh, pretty

I put new brake pads and rotors on the front of the van today. No big deal but I wanted to post this photo. I love fresh, nice looking machined parts. Sooooo pretty....

Saturday, March 29, 2014

Printed folding hinge

I was asked by my wife to print a display stand for this little doll.  The design I came up with prints flat then folds into position using a printed hinge.  I think it's kind of clever, though certainly not unique.

The hinge is a separate module in the SCAD so it can be used in other print flat designs. I'm sure it could use some improvement but it works for this application.

Here's the design on Youmagine.

Here's what the hinge looks like close up.  It folds up and locks into place.

USB battery bank

My new Nexus 5 eats through its battery a bit faster than I'm used to, and I've been thinking about getting a power bank for a while anyway, so I decided to look around earlier this week.  I went for a cheapo off eBay.  The unit pictured below cost $18 shipped from a US vendor.

It seems to work just fine. I plugged my phone in at 71% charge, the battery bank arrived showing 55% charge.  I used the 2.1A plug, it topped the phone up in less than an hour and the battery bank still shows 54% charge. It claims 12000 mAH.  From the size of the thing, I'd guess that it holds four 18650 cells, so that does put it over 10,000 mAH at least, though not at 5 volts, but you totally expect these things to be rated in the most over-the-top way they can vaguely justify.  In any case it should be able to quickly boost a dead phone up, and it should be able to do it at least 4 or 5 times before being dead itself.  For < $20, I'd call it a winner.

The LCD is backlit, the backlight times out after about 15 seconds and the LCD continues to display. It shows if you have something plugged into the 1A or the 2.1A socket (I assume both can be used at once). It has a little LED flashlight that can be switched on/off by double-clicking the power button from either on or off state, and a long press on the power button turns the unit off.  The unit also powers itself down after the power draw goes away, though I doubt it would shut down when the phone is done charging since I think most phones are going to keep drawing a little power.

It comes with a short USB power only cable with tips for MicroUSB, MiniUSB, Apple and a little coax that I've seen used by Kyocera and a few other things.  The power-only cable is also useful for using with public charging points if you're paranoid about plugging your phone into a random wild USB socket (since it's possible to build such a point that would strip data from your phone or even infect it if you use a full data/sync cable).

FOLLOW UP: It doesn't actually have all that much capacity. I plugged my phone in last night at 30% charge. In the morning my phone was at 100%, the bank said 74%.  This evening I plugged the phone in at 28%, and the bank went dead with the phone still at 80%.  Maybe a few cycles will improve it, but probably not all that much.  It seems to have perhaps 5000 mAH at 5V, which at 100% efficiency would translate to about 7000 at 3.6v (which the cells inside would nominally be at) not the 12000 that they claim.  If it had really good cells inside, like Panasonics or something, it might reach 12000.  Still, it's fine for my purposes and I can't complain for the money. You have to realize going in that these things have ridiculous ratings, like the $20 eBay bike headlights that are rated at "2100 lumens" - they actually put out about 1000 lumens, which seems bad but even 1000 lumens for that money is a good deal.  Just realize when you buy that specs from these places are generally overstated by as much as double.

Saturday, March 22, 2014

Having the right tool

I did a couple of quick plumbing jobs today and the value of having the right tool really was apparent.  The weird yellow thing on top is a thing you shove down a drain and it snags whatever's down there clogging things up.  If your tolerance for "yuck" is high, it will clear a drain in about 5 seconds.  If your tolerance is not high, you probably don't want to clear a drain anyway.

The bottom thing is a core puller for Moen faucets.  Last year I replaced a core on the kitchen faucet without a puller, it took me about 90 minutes and I wound up basically recreating a crude puller out of threaded rod and random tools, a block of wood and a pry bar.  This time I spent $12 and pulled the core out in about 2 minutes.  This one was more stubborn than the last and I'm pretty sure I would never have been able to get it out without the right tool.  As a result the house water was only off for about 10 minutes.

Get the right tool, you'll save time and possibly money.

Monday, March 17, 2014

16 RGB blinkie take two

The previous multiplex circuit wasn't working out. I was doing a modified CharliePlex but with the different colors (with different forward voltages) involved and the common anode configuration, I couldn't avoid ghosting while driving 16 RGB LEDs from 8 I/O pins.

This one uses a 74HC595 chip, I'll be using a 74HC164 in the final design to save another 20 or 30 cents. The code to drive this is far simpler, the board layout should be almost trivial to do in comparison to the other one, and the performance is better.  The extra chip only adds about 30 cents to the whole board.

Monday, March 10, 2014

Phone screen replacement: Nexus S D720

One of the phones in our house got dropped a few days ago and the screen broke. It's a Samsung Nexus S.

I picked up a "hard bricked" Nexus S on eBay for $25 and swapped mainboards.  Back up and running, no problem, about 20 minutes to do the swap including putting the now doubly-broken phone back together. 6 screws and some prying on the case get you into the back, three more screws and some popped connectors get the mainboard off.  Very easy replacement.

If you have a broken screen on a device, check YouTube for disassembly or screen replacement on the device model and you'll see exactly how hard it is to do and you can judge if it's something you can do yourself.  I did an iPhone 4 last year and it was a chrome-plated pain in the butt. I did a Samsung Galaxy SII a few months ago and it was super easy.  This Nexus S was a little harder but nowhere near the iPhone.

Sunday, March 9, 2014

Blinkie 2014 #1

This one is pretty much done. I might write a few more patterns, and there's one little bug that I need to fix that causes the switch to be a little jumpy, but it's ready for production.

Here's the pre-production prototype:
The code and design files for this blinkie are not 100% complete as of this date but should be within a few weeks.  They will be found on GitHub here. Once I've finalized this and sent it to production I'll upload the KiCAD and Gerber files.

Here's the schematic:

Tuesday, March 4, 2014

16 RGB LEDs running on an ATTiny84

As an experiment, I wanted to get 16 RGB LEDs running off a relatively small microcontroller.  I got it going with an ATTiny84 using 8 I/O pins (leaving the ISP pins alone).

I had to boost the CPU speed from 1 to 4 MHz (it will run up to 8 MHz on the internal oscillator depending on how the prescaler is set).  I'm not sure if I'm going to wind up using this or not.  It is extremely cheap to build a flashy device with this method but the chip only has 8K of flash and I've used up 6.5K with the color rotation code and the display routine.  I think half of that is the color rotation, it's using some math libs, so probably I could trim that down.

The alternative is to use WS2812Bs which are super sweet but not cheap - they would about double the price of the device, and if I'm going to do that, I will probably go ahead and spend the extra dollar or so, use an ATMega328 and make it Arduino compatible.

New printer: JGAurora A3

This week I decided I'd had it with all the other printers in my stable.  The CTC is stable and decent but it just bugs me (can't st...