Superprobe meets vintage multimeter

One of the first tools I built myself many, many (decades!) years ago was a logic probe. At the time things like yellow LEDs were still a bit rare and cool, but this baby had both red, yellow and green LEDs to indicate TTL logic levels. It was a true rat’s nest of wires – and everything stuffed into one of those plastic cases for one-time travel toothbrush that you (used to) get at some hotels. A stiff copper wire was glued to one end of the case. Ugly as h-ll, but it worked quite nicely.

Years have passed, and I actually found that probe a year or so ago. It still worked, but with access to things like multi-channel logic analysers and digital storage oscilloscopes, that probe was sent to rest at the place where electronics never return from.

Still, the basic concept of a logic probe IS kind of nice. And as some people have taken this concept and extended it to include a bunch of other tools in the same circuit, I thought I’d spend some time building a new probe.

It’s really just a Superprobe in a somewhat unique (probably not, but I like the concept..) case. The Superprobe exists in various flavours, the ones I’ve liked best so far are the original onethe MKII one, and the one from Dangerous Prototypes.  The one I built is a mashup of the three, dropping the voltage reg (as I feed my probe from a USB cable, which provide a stable +5V that the PIC can use. Adding programming headers á la the DP probe was a must-have. But dropping the display resistors, seems to work just fine without them.

The project really kicked off when I was cleaning out some boxes of old stuff, and found the first digital multimeter I ever bought, probably around 1985 or so. It is a total piece of junk, was probably the same back then, but still expensive at the time. Interestingly enough, the main ADC chip of the DMM was a MAX131CPL – which is still available for purchase today!!

Off to work then.
After ripping apart the DMM and stripping away all components, LCD, daughter boards etc (all through-hole components, of course. This is pre-SMD times.) I was left with some space in the DMM that should nicely handle the Superprobe circuitry. It might even be possible to squeeze a Dangerous Prototypes Part Ninja in there, and then multiplex the display between the two tools… Nah, one thing at a time, I’d rather finish the probe first.

It all comes together quite nicely, with a mini USB jack providing power to the probe, the probe’s two push buttons are hot glued to the upper left/right sides of the case, making it easy to operate them both when the meter is on a table, and when it’s held in hand (in that caseit’s actually possible to operate the whole probe with a single hand, using thumb and index finger, while the probe rests in the palm. Nice!).
The input jacks from the original DMM are re-used and soldered to the input and Gnd of the probe, with one of the original mechanical range switches wired as on/off for the probe.

Works like a charm, the pictures below show the probe while in use.
Only one small glitch, not sure what’s going on. When the probe is turned off, it needs a minute or two before it agrees to turn on again. Some capacitor that need time to discharge, I guess. Thinking about adding a reset button.. should be an easy thing to add, just hooking pin 1 to ground through a small push button.

All in all – nice little project that is likely to be quite useful up ahead.

Reverse engineering Macbook Air FaceTime camera, part 1

A severely cracked 13″ Macbook Air display came my way some time back. The LCD panel was obviously damaged, but it would be interesting to see what makes such a great display tick, and maybe parts of it could still be used? I believe the display came from a Late 2010 Macbook Air (which would indicate an A1369 type construction), but can’t be sure. Anyway – ideas included

  • Keeping the back lighting (assuming it works) and camera, mounting the whole display on a flexible arm next to the work bench. Given the high intensity of the back lighting, it could then (maybe) provide ambient lighting AND video recording of whatever was being worked on. Maybe with a LED light and camera on a separate flexible arms.
  • If the LED backlighting drivers were toast, there should still be some nice white LEDs in there for scavenging.
  • Same thing for the camera, I believe it to be a 640×480 pixel device, nothing too exiting but could still be useful.

Turns out it’s not entirely easy to disassemble these displays. They are sealed together with very strong tape. Heating the bezel helps a lot, but it’s still a fair amount of work – and given the delicate components beneath the bezel, you might want to think twice before doing this on a laptop you care about.. Some good instructions found here, btw. Results so far:

2013-02-19_10-41-22_smallPrying the bezel open…

…before applying heat with a hot-air SMD rework station (regular heat gun would probably also work, if you are careful):
2013-02-19_10-44-38_small

Voila! Bezel is free:
2013-02-19_10-56-14_small

Now the tricky part. The cable from the cable is a thin wire with some kind of textile cover, for strengths I assume. It goes through the hinges and there is no way (as far as I can tell) to get the cable through there, without cutting off the (very small) connector that normally connects to the computers Left I/O (a.k.a. LIO) board. Cut.

Now the whole camera assembly can be removed. It also includes the ambient light sensor, which communicates over I2C. Unknown protocol for that one though – one for the future to investigate..

2013-02-23_22-55-38_small
Very tiny 6-pin connector, normally going to the LIO board.
2013-02-19_13-11-34_smallCamera module exposed in the top part of the screen. Held in place with 2 small screws.


2013-02-23_22-32-08_smallCamera board. 

2013-02-19_13-17-59_smallThese things are small – fingers included for scale reference.

With six wires in the cable it’s pretty clear that 4 are for USB (+5V, Gnd, Data+, Data-) and 2 for I2C. That cable is however crazy small – it’s about 2 mm diameter. Once the outer layer is off, you see 6 even thinner cables. 2 are black, 4 transparent. Which ones are which?

Google is your friend. Turns out there are schematics to be found if you Google long enough. Turns out you need schematics for the LIO board though, in order to get the pinout of the camera/ALS cable, and it’s nowhere to be found for the A1369. Did find a schematic for the A1370 model though (same computer but 11″ screen), with a bit of luck that cable is the same between models.

The 2 black ones are prime candidates for +5V and Gnd. Cutting away the insulation revealed that the cables are shielded, with a center wire that is barely visible to the eye. It took several attempts before I had separated the wires from the sheilding, and then done the same with the other 4 wires. Soldering these onto an old USB cable was then easy (but ugly!!):

2013-02-28_14-09-48_small

Still, it doesn’t work. The camera is not recognised on an iMac with latest OSX, nor on a Windows 8 laptop. Happened to have a Raspberry Pi lying on the work bench, tried it too with same result: nothing.

But wait… doing a “tail -f /var/log/messages” on the RPi showed that it DID recognise the camera, but that the camera wanted more power than a non-powered USB hub could provide! Placing the camera into the RPi’s regular USB port made it appear nicely when doing a “lsusb” command.

Still, it didn’t work when I connected the camera to the Windows or iMac machines – strange.

Also, the RPi loose contact with the camera after a while – no idea why. Could maybe be a bad USB cable (it’s from an old mouse using USB 1.1 – maybe that’s a problem??), or is there too much noise introduced by the ugly splicing of cables that I’ve done? No idea… More investigation needed. Anyway, the camera enumerates with USB id 05ac:850a, which indeed is an Apple FaceTime camera – nice!

Smoke tester from Dangerous Prototypes

A while back I got a free PCB from Dangerous Prototype’s Free PCB program. It’s a nice little board designed to provide easy current monitoring during prototype stages of a project. Features include over-current tripping with visual indication, as well as dual 5V and 3.3V supplies.

So, a week or two ago I was about to reverse engineer a laptop camera (built with very small components…). The camera’s attaching cable has unknown pinout, but system block diagram indicate it’s a USB 2.0 device. The cable is a 6-wire variant, so it shouldn’t be too hard figuring out which wire does what. It would however be nice to have a controlled power source feeding the camera during the work.

Enter the smoke tester… I figured I would build it, to the extent possible, with parts already found in the lab, if needed maybe even scavenging some old computer or similar..

The result is pretty nice:

smoke_tester_20130227

Some comments/feedback on the design:

  • Input power screw terminals don’t have +/- marked on the board.
  • Holes for bana jacks too small for any of the jacks I’ve tried.
  • Really nice with the three parallel pads for INA 138 load resistors. They give good flexibility for selecting shunt resistors for the INA 138. For example, I used a 0.1 ohm (instead of 0.075 ohm as suggested in the schematic) shunt resistor, which means the load resistor should be 50 kohm. Easy – two 100 kohm resistors in parallel does the trick.
  • Documentation is very limited, basically just a forum thread and schematics (that don’t include all component values, e.g. R13 and R14.

A few components are missing on thew board:

  • USB out connector. I had a hard time finding an SMD connector that would work. Figured I’d mainly be using the screw terminals anyway.
  • Banana jacks. Going through the parts bins here, all the banana jacks were too big to fit in the PCB’s holes. Those wholes could be a bit larger, IMHO.
  • Input power jack. Couldn’t find a suitable SMD one, but as I will be taking power from a wall wart with USB output I will be fine.
  • R13, R14. There is no value for these in the schematics (as far as I can tell), leaving them out thus. But as the USB out connector is unpopulated anyway, it’s not a problem (right now). Edit: They should be ca 20 ohms.

Links:
Dangerous Prototype’s forum page

Wiring the house, part 3: Planning the 1-wire sensor network

When ordering the needed hardware new possibilities came to mind, as they so often do when you are browsing catalogs of companies selling cool gadgets…

The first version of the 1-wire network will look something like this, possibly with some of the sensors furthest away from the server installed at a later time. Some of these sensors are after all pretty expensive (just the humidity sensor, HIH-4000-001, got it from Digikey, that is attached to the DS2438 AD converter cost around €20). Getting the all the cables in place have also turned out to be a bit tricky, the tubing in the walls back in –65 just weren’t made with cat-6 networks, phone lines and 1-wire networks in mind…

SP53 1-wire network

The Linux server will run either temploggerd and owfs (if I can get it to work on the small Bubba Linux server that I am using, so far it compiles ok but doesn’t seem to respond properly to the sensors), or thermd.

I verified thermd runs (it does work as expected but it takes 15-20 seconds or so to update the graphs) on the Bubba server as long as you install the perl runtimes and quite a few Perl packages, but as owfs offers a better client-server approach it would be the preferred solution.

Wiring the house, part 2: Buying 1-wire sensors and accessories

So, having moved from a flat to a house a couple of months back it was time to do some actual work on a home monitoring system.

First task: to find a good source for the needed 1-wire sensors and other electronics and hardware.
Some digging around, comparing a lot of prices resulted in the matrix below.
I then ended up buying my 1-wire products and components from Homechip and Hobby-boards, with some additional components from Electrokit.

Please note that prices and other aspects of the stores are expected to change, the data below represent a snapshot as of August 2009. They should in any case provide some starting points for your own 1-wire online shopping adventures.

Vendor Country Comment
Homechip UK Good prices and fast, affordable delivery across Europe, they don’t have quite the selection of 1-wire products as for example Hobby-Boards or DigiKey (who are outstanding when it comes to components).
But with Homechip offering the core component I needed while also being European the first batch of 1-wire sensors were bought from them. Might try other providers later.A good thing about Homechip is that they carry the
T-sense (made by IButtonLink) at an affordable price. VERY convenient temperature sensor! Ok, a bit more expensive than buying the components, but oh so convenient..
Low shipping costs also to rest of Europe outside of UK.
Hobby-Boards US Nice store with some assembled and ready-to-go 1-wire sensor modules, such as the 8 channel relay board or the nice little DS2423-based dual counter(Note: Homechip carries a similar counter).A GREAT thing about Hobby-Boards is that they offer both schematics and PCB layout for free on their web! This gives some very good inspiration for those of us who like to build things from scratch but have spent the last fifteen years doing other things than designing electronic circuits.Reasonable prices but longer/more expensive shipping if you are in Europe.
Embedded Data Systems US This company among other things makes the HA7Net, which is an Ethernet equipped 1-wire master controller with some real intelligence in it. It contains a web server, upgradable firmware, various tools for reading/writing/maintaining a 1-wire network. The HA7Net also has three 1-wire ports, making it dead simple to create a star-formed 1-wire network.The HA7Net acts as the 1-wire centre point in my network, it is then read by various other software on the internal TCP/IP network.
Temperatur.nu Sweden temperatur.nu contains both temperatures across Sweden updated by people’s personal computer connected weather stations, as well as an online shop and a good forum for Swedes interested in home and weather monitoring systems. Quite a few good 1-wire related threads in the forums.The store has a fair number of components as well as pre-assembled sensor modules. Prices are a bit high compared to for example Homechip but if you are in Sweden and need fast delivery it may be worth it.
The store also has various home automation products, such as radio controlled 220V switches.
IbuttonLink US Makers of some good 1-wire products, such as the LinkUSB 1-wire interface, which can be used instead of the standard DS9490R from Maxim. They also make the very convenient T-Sense temperature sensor, but as this is available from HomeChip at the same or even better price (given the current USD to EUR exchange rate), I’ve got my T-Sensors from Homechip.
1.wire shop Germany Expensive German online store
Fuchs Shop Germany Expensive German online store
SparkFun US GREAT company with a fantastic amount of cool gadgets and electronics kits in the store, usually with very affordable prices. If you like fiddling around with electronics and microcontrollers you’ll love SparkFun. SparkFun offer free schematics for many of their kits, they also have good tutorials and forums. Great site!
Digikey US
Intl
Giant retailer of electronics components. More than 1900 employees, more than 450.000 products in stock. If you need an electronics component, Digikey is likely to have it, and at a good price. Based in US means longer delivery and higher shipping costs though.
Edit: Turns out Digikey has a great international service as well! For their Swedish customers they even offer free shipping on orders of more than €65, which is pretty easy to reach when looking through their catalog…
Electrokit Sweden Probably Sweden’s best online store for electronics components and Arduino microcontrollers. Good prices, very affordable shipping costs.
Lawicel-shop Sweden Sells various embedded systems products, including Arduino boards. Seem to be more expensive than Electrokit.
Maplin UK Sells all sorts of electronics and components. Might be worth considering for UK people.
Energibutiken Sweden Online store with a small but fairly good selection of products relating to energy monitoring. They among other things have an interesting data logger for those who don’t want to be bothered by running a server for their 1-wire projects.

Wiring the house

Moving to a house from an apartment made me realize you have new things to consider.

– How much money is spent on heating?

– We have a 45-year old, huge water boiler in the basement, how much does it cost to keep it running? Would we save money by replacing it with a modern one?

– It is said that return-on-investment on air-air heat pumps is quite short, around 18 months is often mentioned. But before installing such a pump to reduce the need for electrical heating it would be great to have a system in place measuring how much electricity is used for electrical heating before and after the pump is installed, and how much energy the pump itself uses.

– How do you measure the above, collect the data and present it in a good way?

– After installing radio controlled switches across the house, how do you control them in a good way? The included remote works ok, but a computer interface is really what is needed to create more advanced lightning setups.

In the coming posts I’ll sum up the experiences made in planning, building, configuring and running the above services. Having searched the net for information and experiences from others I have found some, but not a whole lot. Hopefully my findings will help others with similar plans and ideas.