Rocket instrumentation project (v0.2)

Thanks to Mike, and Andy, and Jon, and our other fellow hackers for their inspiration and advice and ideas and everything else. I just laid out a board, but I can by no means take all the credit for the project idea.

Unless otherwise specified, you may consider the hardware designs linked here as licensed under the TAPR Open Hardware License.

I know EAGLE isn’t FOSS, so if you’re eally principled about not using any software that isn’t open, unfortunately you won’t be able to open those files. I haven’t learned to use gEDA yet. If you want to, by all means, feel free to re-draw the board and schematic layouts in gEDA, using the PNG images provided.

Schematic (moderately large .png)

PCB layout (moderately large .png)

EAGLE schematic file.
EAGLE board file.

That board design has everything routed…. it’s complete. Yay :)

i) Temperature sensor.
Here I’ve just assumed that we can use a DS18B20 to measure temperature; pretty simple really, just one microcontroller pin, and a 4.7 k pull-up resistor. We could of course have multiple sensors throughout the rocket and just bus them all together, and connect them all back to the one connector on the main PCB. There are other sensors we could use in theory, but the DS18B20 is common, convenient to use, and there is heaps of experience and documentation with regards to using it in the Arduino community.

I didn’t have a part library for the DS18B20, so I just put a 3-pin 0.1″ pin header on the board. You can simply solder the TO-92 package through that footprint on the board quite easily, or alternatively, you can stick a pin header on the board, and wire up the DS18B20(s) off the board.

ii) GPS.
Here I’ve just picked LS20031 5 Hz GPS from SparkFun, since Jon mention that’s the one he has experimented with.
It’s a 3.3V device, so we simply have a 1:2 voltage divider on its RX line to interface it to the 5V microcontroller.
I’ve just used a standard 0.1″ pin header footprint here, so flying wires can be soldered on to connect to the pads
on the GPS board.

Since the microcontroller on the Arduino only has one hard UART, a virtual soft UART needs to be used, and the performance that you programming gurus could squeeze out of that code will be the factor that limits the speed at which the GPS could be read. It’s not my department :)

iii) Light sensors.
Just two LDRs connected to two microcontroller ADC inputs, connected with a couple of resistors as voltage dividers. Pretty simple, really. The resistor values might need to be tweaked depending on the typical resistances of the LDRs used, but they should be pretty flexible, and 100 k should be about right, since we really only want qualitative information from them anyway. The LDRs can of course be mounted off the board on long flying wires, and mounted whereever they have to be mounted.

iv) Real-time clock.
I’ve just assumed we’re using a DS1307 here, and this is really just a very simple schematic which is needed to support this device. There are a couple of 10 k pull-up resistors on the I2C bus. You could use any DS1307 prototyping or development board, as available, for example, from Sparkfun or Microzed or Futurelec, to develop code for this, they’re all the same chip, and they all have essentially identical hardware.

v) Flash memory.
Mike mentioned the AT45DB61B, and that looks like the perfect device.

It has heaps of storage, it’s fast, it’s easy to interface, and it’s inexpensive. There’s nothing not to like with this suggestion. This is a 3.3 V device, however, but the datasheet says that the communications signals are 5 V tolerant, so there shouldn’t be any trouble with interfacing it. 2 Mb ought to be enough for anything (touch wood) but if it isn’t, there’s no reason why another chip couldn’t be added on the SPI bus.

Rockby sells the device in the CASON package for $2.60 AUD, and Sparkfun sells the same device in the SOIC package for $3.60 AUD. Since the latter isn’t far more expensive, and the CASON package looks like it’s a bitch to solder by hand, I have used the SOIC package :)

vi) RF telemetry.
Here, just for the sake of drawing the schematic, I’ve assumed we might be using an XBee device, although if you wanted to change the design to use, say, one of the DR3100 devices there wouldn’t be much of a change, they’re still 3 V devices, using bidirectional serial comms back to the microcontroller, so there really isn’t much difference. The XBees have a couple of LEDs to indicate their status, eg. that they’ve got a communication link to another device, so I’ve just added these in, since a few blinkenlights don’t hurt :)

Note that the XBee is a 3.3V device, so I’ve just divided the data input from the microcontroller down with a 2:1 voltage divider, which should be fine.

vii) Microcontroller
Here I’ve just assumed that a standard Arduino Duemilanove board is used. I’ve especially chosen the pins allocated for the I2C and SPI buses to correspond to the AVR’s pins for those hardware interfaces, although if these interfaces were implemented in software, any other pins could be used, really. There’s a reset button included, since the shield board blocks the one on the Arduino itself.

viii) Accelerometer and ADCs.
I’ve just assumed we’re using an ADXL330, and the LTC1298s as Mike mentioned, which is a cool idea.

I chose the ADXL330 pretty much arbitrarily, since it’s the first one I could find an Eagle library for, it seems pretty common, and SparkFun stock it. It’s the same 3-axis accelerometer as used, for example, in the Arduino Lillypad accelerometer board.

The Analog Devices ADXL345, with A-D conversion built in to the IC with only an interface to the microcontroller’s SPI or I²C bus needed, looks very cool though, and the price difference, once the cost of ADC chips is included, doesn’t seem that large.

ix) Barometric pressure sensor.
This is just a Freescale MPX4115, which seems somewhat common in UAV, model aircraft and rocketry work for altimeter applications.

I’ve put a bit of low-pass RC filtering on the output from the barometric sensor, using the component values just as given from Freescale AN146. I’m currently working out the maths to read out the altitude from the output from the barometric sensor, which isn’t that trivial.

ix) Power supply
I’ve removed the LiPo battery and SMPS power supply from the previous version, since we need a 12V battery for the video downlink anyway.

I’ve just assumed that 12 V is plugged into the Arduino’s power supply jack, and 5 V is coupled to the daughterboard via the Arduino’s pin headers. There’s a 3.3V regulator on the board supplying the 3.3V for the XBee and accelerometer and DataFlash, an LM1117 at this point, although you could swap it for some other kind of device that is available. It needs to be a low dropout regulator, though, since you’re taking a 5V input to regulate down to 3.3 V.

The Vin pin on the Arduino is connected to one of the analog input pins via a voltage divider, so that battery voltage can be measured by the Arduino. (I know, those pins are right next to each other, and this seemed like something of a sweet hack.) With those resistor values chosen at the moment, 12 V on Vin corresponds to about 4.53 V on the ADC input, so you can read it straight off. Actually, Vin won’t be exactly equal to the battery voltage, because there’s a polarity protection diode on the Arduino power input before that Vin pin connection…. so there will be a little drop across that. I don’t know exactly how much, maybe about 0.2 V for a Schottky diode, I haven’t empirically measured it.

Now, what to call this thing? “That Arduino based rocket instrumentation/datalogger project” is too much of a mouthful. So, we need a name.

How about, say, ARTEMIS. That is, Arduino Rocket Telemetry and Instrumentation System.
(You can totally see the experimental physicist in me reflected in that name, can’t you?)

That’s just my idea for a name. I’ll let the Hackerspace crew mull over it and come up with a better idea if they want to.

Bill of materials… for the design as it stands at present.

Resistors: (All resistors 0805 SMD package)

R1      4.7 k
R2      100 k
R3      100 k
R4      750 R
R5      10 k
R6      10 k
R7      100 k
R8      100 k
R9      56 R
R10     100 k

R11     56 R
R12     100 k
R13     150 k
R14     91 k

Capacitors:

C1      10 uF 16 V tantalum, through-hole                                       Jaycar RZ-6648
C2      10 uF 16 V tantalum, through-hole                                       Jaycar RZ-6648
C3      100 nF, 0805 SMD package
C4      100 nF, 0805 SMD package
C5      100 nF, 0805 SMD package
C6      100 nF, 0805 SMD package
C7      100 nF, 0805 SMD package
C8      1 uF, 25 V tantalum, through-hole                                       Jaycar RZ-6627
C9      10 nF, 0805 SMD package
C10     330 nF, 0805 SMD package
C11     100 nF, 0805 SMD package
C12     100 nF, 0805 SMD package
C13     100 nF, 0805 SMD package

ICs:

I've specified some examples of parts suppliers that I know have the relevant items, though they may not be the only choices, or the best choices.

IC1     Linear LM1117-3.3 LDO 3.3 V voltage regulator, SOT-223 package          Digikey LM1117MP-3.3CT-ND
IC2     Dallas DS18B20 1-Wire temperature sensor, TO-92 package                 Sparkfun SEN-00245
IC3     Linear LTC1298 analog-to-digital converter, DIP-8 package               Futurelec
IC4     Analog Devices ADXL330 3-axis accelerometer, LFCSP-16 package           Sparkfun COM-00730
IC5     Freescale MPX4115A barometric pressure sensor, 867-H package            Digikey
IC6     Linear LTC1298 analog-to-digital converter, DIP-8 package               Futurelec
IC7     Dallas DS1307 real-time clock, SOIC-8 package                           Futurelec
IC8     Atmel AT45DB161B 16 MBit DataFlash memory, SOIC-8 package               Sparkfun COM-00301

IC9     Arduino Duemilanove board
IC10    XBee module (any, really)
GPS     LS20031 GPS module                                                      Sparkfun GPS-08975

B1      12 mm coin cell holder, SMD                                             Sparkfun PRT-07948
plus CR1225 3 V lithium coin cell                                       Sparkfun PRT-00337
Q1      32.768 kHz quartz oscillator crystal, TC-38 through-hole package        Sparkfun COM-00540
S1      Momentary tactile pushbutton switch, through-hole                       Jaycar SP-0600
LDR1    Standard cadmium sulfide photoresistor, through-hole 0.1"               Jaycar RD-3480
LDR2    Standard cadmium sulfide photoresistor, through-hole 0.1"               Jaycar RD-3480
LED1    Standard LED; 3 mm through-hole                                         Jaycar ZD-0120
LED2    Standard LED; 3 mm through-hole                                         Jaycar ZD-0120

2 x 10-pin 2 mm header sockets for XBee module                                  Sparkfun PRT-08272
Break-away 0.1" machined pin socket strip for mounting LTC1298 ICs              Jaycar PI-6470
28-pin break-away 0.1" pin header strip for mounting shield to Arduino          Jaycar HM-3211

This is your new computational god.

This is Wolfram Alpha. And it’s omg-shit-that’s-awesome.

It’s everything that Google Calculator could have been but never was.

The economics of home solar PV installations

As most of you are aware, there are heaps of companies out there lining up to install solar photovoltaic grid-connected systems on your house, typically of 1 kW, since that’s the maximum size that the government subsidy is capped at, and the government rebate of $8/W for such installations seems pretty attractive.

The out-of-pocket costs for installation of these systems range from about $3000 to $5000, although some companies offer such systems for essentially nothing, only $500 or so for the meter upgrade, after the rebate is repaid.

These guys sell their basic 1 kW system for $5000 out-of-pocket after the subsidies and rebates, and these guys sell their systems for $3000 after rebate.

For most of these systems, the average cost advertised, the out-of-pocket final cost after the subsidies have been taken off, is about $3000 depending on the quality of the system.

Personally, in the case of the systems advertised for zero overall cost, I’d be a little bit worried about the quality of the system, since they’d have to be honing the price down quite a bit to get it down to the point where they can pay for it, pay for installation, and still make a profit, just from the $9000 or so in the government handouts.

You wouldn’t want a shonky system that burns down your house, would you?

In southeastern Australia, including Melbourne, Adelaide, Sydney and everything in between, the average daily solar exposure is 15 megajoules per square meter per day.

So, that’s an average power density of 174 W/m², on average, over the whole day.

Now, if you buy a solar PV module that is rated at 180 W, or whatever power figure it is, you get that amount of power if there is 1000 W/m² of solar radiation incident onto the panel.

So, a “1000 W” array, in the real world with an average of 174 W/m² worth of incident radiation flux, will generate 174 W of power, on average. (Averaged over the full 24 hours in a day.)

Therefore, you get about 1500 kWh of total energy generation per year.

If you’re paying, say, 13 c/kWh for electricity, you save about $195 per year on the electricity bills.
(I know that’s a relatively low price for household electricity, but it’s about right for Victoria’s inexpensive electricity, powered by the Latrobe valley’s incredible combustible mud. If your electricity prices are considerably higher, you can see how to repeat the calculations for your electricity price.)

If you pay about $3000 out-of-pocket for such a system, then, it will take 16 years to pay for itself.

However, after about 10 years, the grid-connect inverter will die (These guys have a 5 year warranty on theirs), and there won’t be a subsidy paying for that, so that’s probably another $2000 or so you’ll need to shell out. So, that adds another 10 years to the payback time. You probably won’t even be able to pay it off before that second inverter reaches the end of its life.

There are installers that offer higher quality inverters with longer warranties, but they are the higher end of the price brackets for the systems – this is the catch with the extremely cheap systems.

So you’re looking at a payback time of 26 years, for a system where the solar cells are unlikely to last more than 20-25 years.

Such systems, in all likelihood, are never going to pay themselves off, even with the huge government subsidies.

All these businesses that are doing the installations are literally leeching off the huge government subsidies; if you took away the subsidies they would all disappear straight away.

With a saving of close to $200 per annum off your electricity bill, if the customers had to pay the $8000 which is subsidized by the government, just that $8000 portion alone would take 40 years to pay off, and you would never, ever even come remotely close to paying it off.

This scheme is just a huge money sink for the government; it’s completely unsustainable, and it doesn’t accomplish anything meaningful.

Customers love it, since they’re effectively getting this huge investment mostly given to them by the government.

It’s just like Krudd’s economic stimulus handouts – people are getting a generous free handout, so they think that’s fantastic, and people will very rarely stop and question whether this actually makes sense as a worthwhile thing for the good of the country.

One of these systems generates about 1500 kilowatt-hours per year.

In 2006, the electricity output sent to the grid from Loy Yang A, just as a typical example, was 15,995 gigawatt-hours.

Therefore, if you wanted to generate the same amount of energy from 1 kW solar PV installations as just one coal-fired power station, you’d need 10.7 million of these installations. That’s significantly more than the number of households in this country.

You would need just under 11 million typical household 1 kW rooftop solar PV installations – well in excess of the number of households in the country – to give you the same amount of electricity as one coal-fired power station.

Even if you could do that – which you can’t – that still doesn’t give you the means to replace the coal-fired power station, because it isn’t high capacity factor, baseload, generation. You still need that high capacity factor baseload generation to back you up when the photovoltaics are delivering less energy, or no energy at all.

If the government paid out the $8000 subsidies for 10.7 million 1 kW solar panel installations – which aren’t capable of replacing even one coal-fired station – it would cost 86 billion dollars.

This is an enormous amount of money getting flushed away to do nothing in reality, and I’m happy to see it scrapped, personally.

Here’s a contemporary real world example of people buying into “green” ideology without the ability to count kilowatt-hours, and without realising just how damned expensive silicon photovoltaics are. I really, really suggest people do their homework before handing over sums of money like that.

BRISBANE environmental lawyer Jo Bragg and her partner, Gary Kane, spent $28,000 on three roof panels to generate solar power for their home in the inner Brisbane suburb of Highgate Hill.

After receiving a federal government rebate of $8000, they hoped to recover their investment in a cleaner planet within a few years by selling excess power into the mains electricity grid.

In the three months to April, they used 1384 kilowatt hours and produced 388 kilowatt hours of excess power, for which they received the princely sum of $12.96 after taxes.

“Governments are not being serious about reducing energy consumption with lousy amounts of money like that,” Ms Bragg said.

Her family is the kind Kevin Rudd had in mind yesterday when he announced that individuals and households would be part of a revamped carbon pollution reduction scheme.

The Prime Minister said households would be able to calculate their energy use at home and pledge contributions to the $25million energy efficiency savings fund to effectively offset their emissions.

“Individuals will be able to calculate their energy use and establish the savings they could achieve with a more energy-efficient home,” Mr Rudd said.

“A household or individual could then make a tax-deductible donation to the pledge fund, which the fund would use to buy and cancel carbon pollution permits equivalent to that level of energy use.”

Ms Bragg said she hoped the carbon permits scheme would be flexible enough to allow households with renewable energy to be paid for the gross amount of power produced — not just the excess — as happened in Germany and some other countries.

“It makes sense to provide incentives to homes to make it worth their while to invest in renewable energy,” she said.

“Even if we were paid for the gross amount of power produced, it would take us eight or 10 years to recover the investment.”

Obviously, this thirteen dollar figure seems a little bit surprising, so let’s see if we can break it down a little and try and extract some more concrete information about where that figure came from.

The average Australian residential electrical energy consumption is approximately 25 gigajoules per annum, and 1384 kWh over three months is about 80 percent of that, which is plausible for a relatively small, energy-efficient household.

Based on the quoted cost of $28,000 (post-rebate), and the mention of “three roof panels” in the article, I’m going to take an educated guess here and say they have a relatively large system, with 3 kW of installed nameplate capacity.

We’ll assume that the BOM insolation data for February is representative of the average of the three month January-February-March period, meaning that the average insolation is 21 MJ/m²/day, which is 243 W/m² on average, meaning that a “3 kW” nameplate capacity installation will produce 729 W of power on average. Therefore, over three months, the system should produce about 1598 kWh.

Since the Green protagonists of our tale used 1384 kWh and sold back onto the grid 388 kWh of net energy production, the gross energy production from the system was presumably 1772 kWh, which is 111% of the theoretical 1598 kWh. So, these published figures are consistent with the numbers we theoretically expect.

Now, in Queensland, they’re getting paid a special elevated 44 c/kWh feed-in tariff for their net electricity generation from their PV installation. Therefore, their 388 kWh should have earned them 171 dollars. But, ostensibly, it did not. So where did the rest of the revenue, the seemingly missing $158, go?

The answer is that it probably went, I presume, to cover various flat-rate fees included on the electricity bill, such as a service charge, and/or an ambulance levy, or what have you; components of the electricity bill other than the per-kilowatt-hour charge for the energy use. Maybe it seems a little high for that, but we can’t be certain without seeing the actual breakdown of the bill.

Normally, before the PV installation, they’d be paying an electricity bill of about 221 dollars for their 1384 kWh, assuming a rate of about 16 cents per kWh, plus those charges of $158 or so on the bill, or a total of about $379. Now, they’re getting paid 13 dollars for this quarter, not paying any electricity bill at all. Therefore, they’re saving $392 per quarter, or actually somewhat less than that during the winter months since the solar insolation will be less. And they’re complaining about that? Even after getting the free $8000 government rebate and the 44 c/kWh feed-in handout, they’re complaining that that’s not enough and they want more of a free handout, for something that will never make any real contribution towards replacing coal-fired generation?

Let’s suppose, without calculating it accurately, that they save $300 per quarter on average, every quarter. Therefore, paying off their $28,000 system will take just over 23 years; assuming they don’t need to replace the grid-connect inverter in less than that time. They might, maybe, pay the cost of the system off within the operational lifespan of the solar cells. Maybe. That is, assuming that the 44 c/kWh elevated feed-in subsidy continues indefinitely, and they’re really lucky and their inverter doesn’t need to be repaired or replaced within that timeframe.

__________________

Moon (The Movie)

There has not been much mainstream hype about this thus far, but it looks good.

Oh my science.

(Hat tip to Abstruse Goose.)

In other particle physics related news, we have You’re My Higgs (High Energy Love Song), which is an admittedly-not-all-that-bad attempt at a terribly nerdy song.

But, to be honest, when it comes to nerdy songs about experimental particle physics, this guy will always be in second place. Here’s why:

It has just come to my attention that Les Horribles Cernettes now have a YouTube channel. They are not just one of the very first things on the Web, they’re quite possibly one of the nerdiest things I’ve ever seen on the Web. In a good way.

A little Arduino project.

A little multi-channel thermometer based on Arduino, reading temperature off multiple DS18B20 devices on the 1-Wire bus and outputting temperatures to both a LCD module and an array of seven-segment displays, the latter being controlled through a DS7219.

Butting heads with some pro-homeopathy guy.

My recent post about homeopathy for the Young Australian Skeptics attracted some pro-homeopathy guy in the comments thread. It’s a skeptics website, obviously; I’m not sure exactly what he response was expecting to receive.

So, you know, supposedly homeopathy is real, and I’m a mean old bigot. How does it work? Supposedly, the water has a “memory” of the substances you originally put in it, supposedly just like how a piece of ferromagnetic iron “remembers” the Earth’s magnetic field when you heat it up and allow all those magnetic dipoles to align with the Earth’s magnetic field.

Well, I thought a little bit of pwnage was in order. Cue this response:

If water has a magical “memory” of the substances put in it prior to dilution; what is the physical mechanism by which this “memory” occurs? What degrees of freedom do those water molecules possibly have that could store information for an arbitrarily large period of time at room temperature?

If you could “write” information onto water molecules that persisted for an arbitrarily long time at room temperature without decoherence or thermal noise, using a real physical mechanism that actually existed, kind of like ferromagnetism, imagine what we could do with it!

Water data storage, water “hard disks” with enormously high densities, scalable quantum memory as cheap as water. If you want more songs on your iPod, you just put more water in it! Water-based quantum computers that never exhibit decoherence – even at room temperature, or an incredible water-based version of spintronics. Water-based communication with enormously high bandwidths! The potential would be incredible!

A water molecule really doesn’t have that many degrees of freedom. Certainly there are rotational and vibrational degrees of freedom in the molecule, but they’re not isolated thermally from the environment, and any information encoded on them would be destroyed very, very rapidly, just by stochastic thermal fluctuations. The story is much the same for the positional and translational degrees of freedom of the atoms within the molecule.

Electron-spin degrees of freedom? Well, maybe, but those will decohere very rapidly, too, and in any case, spin-flipping would require an applied magnetic field. Similarly for some sort of use of the nuclear spin of hydrogen-1 (with spin-1/2) in natural water. Decoherence times for a nuclear spin will certainly be longer than electron-spin states, but they will still only be milliseconds or seconds at the most, and you’d still need an applied magnetic field to set up the spin states.

How many bits of information do you need to store the “memory” of the original substance, anyway?

I haven’t yet heard the response.

Getting the facts about vaccination.

It has been often claimed by anti-science pro-disease morons such as the “Australian Vaccination Network” and the likes of Jenny McCarthy that “parents aren’t getting the facts” or that “the information isn’t being made available” to parents regarding paediatric vaccinations.

In response to them, I give you this detailed guide prepared by the Australian government in response to common concerns promulgated by the anti-vaccination lobby.

Whilst this guide is prepared for an intended audience of GPs and healthcare practitioners, there’s no reason at all why it can’t be made available to all parents and the general public today. It is packed with plenty of information to give anyone a good basic understandings of the realities of vaccines, and anti-vaccine myths. Sure, it does contain some technical medical language in places, but it’s mostly quite accessible – and if there’s anything in there you don’t understand specifically, just ask your GP or medical professional about it.

(Hat tip to Dr. Rachie for originally posting this :) )

A nice little Arduino hack.

Here’s a nice little Arduino mod I came up with recently.

Firstly, we’re going to need an Arduino. I’ve used an Arduino Duemilanove, like so, but this is applicable to any Arduino with a compatible form factor, such as Arduino Diecimila.

Now, that spacing between the two headers, where pin 7 and pin 8 are, can be a source of frustration, can’t it?

If only it was a 100 thou (0.1″ or 2.54 mm) spacing, just like the spacing of all the other pin headers. Then you could make a quick and cheap “shield” board using 0.1″ matrix board or veroboard, and use all the digital IO pins, for example.

Well, what I did was to take a strip of female 0.1″ right-angle break-away PCB mount header sockets, like this. Finding a supplier for these can be tricky, but I got them from Altronics, in Australia.

Now, cut off a piece that is 8 pins long, and sit that against the existing DIO pin 8-13 header on the Arduino, so that the plastic bodies of the two pin headers are sitting right up against each other, and the right-angle pins stick down over the edge of the Arduino PCB.

I’m sure you can see where we’re going with this.

Now, we’re going to slide the new pin header across just a little bit, towards pin 13, so that the horizontal spacing between the first pin (next to pin 8 ) on the new header and the existing pin 7 on the other header is exactly 0.2 inches. Now we glue the two headers together, using a little cyanoacrylate superglue.

I found that the easiest way to make the assembly stay together in the right position while the glue cures is to first make up a little Arduino daughterboard “shield”, using a piece of 0.1″ matrix board and 0.1″ male header pins. Plug the Arduino (including the newly installed header) onto the daughterboard, and the new header will stay in place, without moving away from the correct 0.1″ spacing, while the glue cures.

Now, on the bottom of the Arduino PCB, we need to bend the pins on the bottom of the header across just a touch, so they align with the existing solder pads on the original female header. Then we simply solder them on, and there you go.

(Note that I’ve added a 100 k pull-down resistor on the Rx line (pin 0). I haven’t tested this yet, but hopefully it will let the Arduino boot up successfully without the USB interface connected, without it getting confused due to the line floating.

We now have an Arduino with headers that are all accessible on an 0.1″ grid spacing. Of course, we can still plug “real” Arduino shields, with the annoyingly nonstandard spacing, into the original headers as well.

(Also note that I’ve added header pins onto the normally unpopulated pads on the PCB near the FTDI chip, bringing out the spare UART lines. I’m not sure what this is good for right now, but I thought I might as well do it while I was attacking the Arduino with a soldering iron.

Extraordinary Clocks and Watches.

This is really neat.

I love weird and unusual (mechanical or electronic) clocks and watches. Here are some more:

Nerdy clocks.

What the hell?

Cathode Ray Tube clock. It’s gorgeous.

An old badass-looking electromechanical binary register display from a Minuteman I missile guidance computer turned into a binary clock. Duck and cover!

The nixie tube watch. Apparently you get in trouble if you wear it at the airport.

I love this seven-segment bookshelf clock.

LED clock with individual digits. This is really cool, but it’s a shame each digit is tethered to a cable. With inexpensive 433 MHz digital transmitter/reciever modules and microcontrollers, you could make it completely wireless pretty easily.http://suck.uk.com/product.php?rangeID=79&showBar=1#

Finally, this post wouldn’t be complete if I didn’t put in a plug for the extraordinary Clock of the Long Now.