LIS302DL - Triple Axis Accelerometer

The LIS302DL is a triple axis I2C accelerometer that you can buy on a breakout board produced by Sparkfun pretty cheaply and is ±2g/±8g selectable. Its is easy to hook it up to an Arduino (SCL - analog pin 5, MOSI - analog pin 4, tie MSIO to VCC for I2C address 29 or gnd for 28).

There are a few handy examples to get started quickly, such as this and this. I had better readings when I turned in the internal filter.

Repairing Sangamo Weston Master V

The old Sangamo Weston Master light meters seem to have a bit of a cult following with the most desirable being the Weston Master V and the Euro-Master (which is still being made!). These are now 40/50 years old most of them are still working fine. All versions of the meter use a selenium cell so no batteries are needed and they seem to stay in reasonable calibration. I was given a Weston Master II in which the meter mechanism was beyond repair but it seemed like such a cool little device I bough a Weston Master V second hand. This turned out to be broken too so I decided to take it apart to have a look. To take these meters apart you need some fine needle-nose pliers and some small side cutters (for gripping the odd shaped screw heads). Firstly you need to unscrew the two hex shaped screws that hold the alloy plate to the back. Once this is off the little door on the back for high/low range comes off. Next unscrew the knurled part in the middle of the dial on the front. Now you can access the two nuts that hold the front on. Once the front it off you can see how everything works.

The cell is sandwiched between a circular copper contact (attached to the single flexible wire you see running under the meter mechanism) and a large sprung metal contact. A stiff wire that runs from near the upper range limiter on the meter to near the scale mechanism completes the circuit. A sprung bar presses on the needle to prevent it moving until you press the button on the side. In the case of my meter the cell had died. To get the cell out you have to take the whole thing apart which is easier than it sounds. I forgot to take any pictures at this point but you simply remove the meter mechanism then keep unscrewing the odd nut/bolt pieces (remembering the order in which everything came out) until you get to the cell. I put in the cell out of my dead Weston Master II and this seemed to work fine, I also cleaned all the contacts etc. The calibration seems pretty good after zeroing it. Most of the internal nuts were loose when I removed them - this seem to be a common problem that stops the meters working. To complete the circuit from the sprung metal contact on the cell to the meter mechanism relies on 2 bolts being on tight. Putting it back together is pretty easy apart from locating the ends of the springs from the door on the back into the holes in the moving part of the scale mechanism.

Shopping for a Renault Megane Scenic...

For a cheap and practical family car a Megane Scenic is pretty hard to beat. They have been around for ages and being really popular finding a decent second hand one should be easy. Being a French car they do have some interesting foibles. From doing a bit of research and test driving an apparently "immaculate" example I discovered some pretty important things to look for when buying one.

Alarm/Immobilizer The Immobilizer is integrated into the ECU and activated via a IR dongle in the key. To replace one of these keys the cost is ~£125 from a Renault dealer. As the immobilizer is integrated into the ECU is cannot be removed but can be deactivated by entering a 4 digit code (every time you turn on the ignition) using a button on the dash. You can get the code from a Renault dealer for ~£30 or various sources online for free. It seems you can get electronic devices that you can wire in that enter this code for you automatically for about £80. If the remote fob doesn't work its batteries could be flat, the fob could be dead, the fob could need re-syncing with the ECU or the IR receiver may be dodgy. A common fault is water ingress into the IR receiver built into the unit near the front courtesy light (water comes through the base of radio aerial which sits above it). Sometimes this can be dried out and sealed, and new unit is £60 from Renault. There is plenty of info online about immobilizer problem and they seem very common. Without 2 working fobs its potentially going to cost lots of time and money.


Engine It seems engine are generally reliable but prone to oil leaks. The timing belt needs changing (petrol engine) at 60,000 miles. They are prone to headgasket failure if the coolant is not changed regularly and kept topped up (as all French engines are). The expansion tank should be free from a coating of red/brown sludge on the inside which indicates it hasn't been looked after and you could be in for trouble. Coolant should always be a strong blue or red color with no sign of contamination. Difficulty starting when the engine is warm is sometimes a problem and needs to be checked.

Body Work They tend to go rusty round the back wheel arches. If the arches have started going you will probably be able to find other spots of rust starting/bubbling around the car. Rust is probably to be expected on a old/cheap/French car but only gets worse with time and is a pain to sort out properly. The paint work is not of brilliant quality so expect scratches etc. French cars are notorious for poorly designed drainage channels through the body which get blocked with dirt over time and cause problems. Brake hard and listen for a sloshing sounds near the front footwells, this indicates that water has collected in the sills and they need draining/sorting out. If the blower only works on the max setting this probably means the drainage channels at the bottom of the windscreen have clogged and water has got into the fan motor (frying the block of resistors used for different fan speeds). This means taking the dash apart to fix it.

Brakes Under heavy braking the car should pull up dead straight even if you take your hands off the steering wheel. If it veers or just one wheel locks up etc then this probably means you have ceased brake calipers slider pins (or the pads are right down or there is a bigger problem with the brake system). This is a common fault on all cars and can be a pain to fix, sometimes requiring new calipers. Brakes should be responsive and take little effort to stop the car.

Misc Air con should get really cold fairly quickly otherwise it is £50+ to have it re-gassed. Turning the steering wheel from lock to lock while stationary should produce no strange noises. Pulling away in 1st with the handbrake on should be difficult otherwise the clutch is worn (or handbrake needs adjusting!). CV joints shouldn't click when accelerating on full lock. Can be problems with the cables inside the back seats for the mechanism to move them up/down so this needs to be checked.

DIY Flash Trigger Safe Sync

Most modern cameras allow a max flash trigger voltage of 6 volts (Canon) or 8 volts (Nikon). The trigger voltage runs between the 2 main pins on the hotshoe of a flash or between the pins on the trigger connector of a studio strobe, shorting these pins together fires the flash. Before digital cameras this was done using a mechanical switch attached to the shutter but now this is done electronically (hence the max voltages). Old strobes use a trigger voltage of anywhere between 12 to 350 volts and this can be checked using a multimeter set on volts DC - using anything above the 6/8v will fry or seriously shorten the life of the trigger circuitry in your digital camera. In order to reduce the sync voltage you need a 'safe sync' there are manufacturers in the US that make these but they are pretty easy (and more importantly, really cheap!) to build one yourself. The simplest one I found was http://www.repairfaq.org/sam/zpaofu1.pdf. The main advantages (compared to ones using an optocoupler) are the parts are easily available and no external battery is needed, sync voltages are reduced to ~4v using the circuit. Pretty much any triac will work, I only had 1M resistors instead or a 10M or 2 x 4.7M so my circuit is bigger than it needs to be. I hooked mine circuit up in the middle of a sync extension cable to make it really easy to use. Obviously I suggest you test the circuit just using your strobe before plugging it into your D-SLR!

Repairing Canon EF 80-200mm F4.5-5.5 Zoom Lens

This is a Canon EF 80-200mm F4.5-55 zoom lens which had water damage/mess on the internal lens elements. Other than grubby lenses this lens work fine so should be simple to fix! First thing to to is take off the rear mount. There are 5 screws on the back plate and 2 hidden ones which hold the connector contacts in place. The mount twists as it comes away. The AF/MF and tricky to get off and real pain to get back on so engages with the mechanism. The screws are #00 Phillips and pretty poor quality. The lens already had a head snapped off one of the rear screws and 2 rounded off inside the lens from someones previous attempts to take is apart. One the tabs are pulled back the connectors pull out and the board comes away. Underneath is the AF motor mechanism, this is held on with 2 screws and simply pulls out. The rear lens element simply unscrews and comes out. Under this is a random springy piece of metal (which I assume this helps stop the rear element unscrewing). The next element is held in by 3 silver screws with a large diameter head, these screws are very poor quality and very easily rounded. Next the front end of the lens is dismantled. The ring at the front of the lens just clips out - there is a small notch to insert a screwdriver. The front element then slides and comes off. There is then a black cover piece which sits in front of the aperture mechanism held on by 3 screws.

I didn't bother taking off the aperture mechanism as the ribbon cable is threaded right through the body to the board at the rear.
Now we can access all the elements to clean them - there is still one element in the lens but this is easy to reach.
Assembly was pretty simple apart from getting the AF/MF switch back in the correct place. The construction of this lens seems pretty cheap and flimsy, it wasn't obvious how to completely strip the lens but I assume there was clips etc.

Fixing Sigma M42 80-200mm Zoom Lens

This old lens had a very sticky aperture and slightly dirty glass - a great excuse to taking it apart to see how it works! First to come off was the rear mount section that attaches to the camera, this has 3 screws which are either anywhere between #0 and #00 philips depending of the quality of your screwdrivers. The screws used throughout the lens appear to be the same head size. Once the back is off you can see the arrangement for controlling aperture, with the back off the lens is in manual and sliding the levers will move the aperture (or not in the case of this lens). After removing a few screws the whole mechanism lifts off. The rubber grip pulls off to reveal a piece of silver tape that holds the two halves of the outer body together. This lens is push/pull zoom and rotating the body alters the focus. It is the end element that moves to focus and this runs on the threads. The lens consists of multiple sets of elements with lugs (nylon disks held on with screws) around the edges. These lugs run in carefully designed and machines grooves in the outer body of the lens. When the outer body is moved the grooves act on the lugs which, in turn, move the elements to give the desired zoom. With the tape off and the first couple of lugs out the outer case comes off. The grooves the lugs run in are now visible. Taking out more of the lugs allows the lens to come apart. The lens is arranged in 3 main outer cylinders which have grooves to move the elements. The elements have 2 sets of lugs, the first hold the lens in place while the second move the element as the body moves. Some lugs run in 2 different cylinders so pretty complicated! Is a pretty simple arrangement with one pin on each side of each aperture blade which run in grooves. Most challenging part was putting it back together as everything has to line up correctly, this took a lot of looking back at pictures (plus some trial and error...). Without taking pictures it would have taken a *long* time to get it back together - there were different size and shape screws and lugs etc. Back together the lens worked great - even with all the grease cleaned out of it!