Connecting to a car with ODB-II

Our Opel/Vauxhall Corsa B (engine X10XE, 55KW, 1.0l, 12V) has a problem: it lights up the MKL (“Motorkontrollleuchte”, the engine control/warning light) when we’ve been trying to accelerate on the Autobahn. In order to diagnose the problem, I wanted to connect to the on-board control unit and read the error code. Unfortunately, connecting to this unit proved to be a mess. It took me a while to realize that we have the only model of Corsa B where you cannot read the error code with a paper clip: the car has a modern interface standard to all cars nowadays, called ODB-II. You cannot read ODB2 data directly, you have to connect to it using a computer.

OBD-II adapter from www.blafusel.de for connecting to the onboard control unit of many cars. For Opel/Vauxhall, you have to us a multiplexer to switch between different pins. On the left, the ExpressCard adapter that allows to connect without timing problems.

The reader required for this can be quite costly – a couple of thousand Euros for the top-of-the-line standalone units. Well, I wasn’t keen on spending more than my car is worth, so I bought a Open Hardware/Source kit from www.blafusel.de. Amazing site with really knowledgeable, helpful people. I’ve paid ~20€ for the kit including cable, casing etc.

Unfortunately, the interface needs a serial port ans is extremly sensitive to timing (as so many low-level programmers/adapters are). But who the hell still has a real serial port on their laptop? I ended up buying severals adapters just to realize that anything USB-based does not work, and that most extension cards for laptops are based on cheap USB-to-serial adapters. Obviously, ExpressCard/PCIe<->USB<->Serial does not have the best timing properties. I found one chipset that does real PCIe<->Serial conversion, it’s the Oxford OxPCIe952. Any card based on this chipset should work with the ODB-II adapter mentioned above (and any other as far as I can tell). I payed about 20€ for the ExpressCard on eBay.

With the adapter, I managed to connect to the engine control unit alright, which allowed to read and delete the error code (P0103). Now I just have to find the reason for this error code…

PS: There’s unfortunately no open-source project for Opel available, but there is a demo version of the common OP-Com software. The ExpressCard adapter works out of the box with Linux (Ububtu 10.4) and Windows (XP).

How-to repair a pizza oven

Our pizza oven broken yesterday. Well, it broke last time we used it, but we didn’t realize before yesterday night (when we had the pizzas already prepared). I started to repair the oven directly yesterday night (it’s quite simple and cheap to do actually), and as our guests were quite interested in the process I figured I post the description here.

Pizza oven "Gala Pizza Pronto"

Oven description: it’s a very cheap “Gala Pizza Pronto” oven with a stone bed. It’s genious for making pizzas yourself; the pizzas turn out to be much like a “real” pizza (and not either dry or overly soft like in a normal oven, and they have a proper bottom).

German disclaimer: Hier geht es um die Reparatur von einem Pizzaofen. Ich beschreibe die Reparatur auf Englisch. Wenn es aber Fragen geben sollte, bin ich natürlich gerne Bereit diese auch auf Deutsch zu beantworten!

French disclaimer: Ici une description comment reparer un four pizza. La description en bas est en englais. Néanmoins, je veux bien repondre à tout les question qui s’est pose en Français!

Step

Open the casing

Cheap bitset with lots of varieties of bits

Most suppliers use special screws for safety (to keep people like us from messing with the interiour). While we’re at it: DISCONNECT THE POWER CORD before opening the casing. If you don’t, well, that would maybe be a Darwin award, but I felt anyways obliged to put this warning here. In my case, the oven had tri-wing screws (see picture).

For repair work, two things are really important to have:

  1. a multimeter (I assume that you know how to use one, if not check for a guide on the internet, e.g., at Sparkfun
  2. a bitset with may different types (see picture, mine cost 10 bucks and has like 8 different bit types)
Step

Trace circuit

Try to trace the circuit of your oven. The circuit of the cheap ovens (like mine) is very simple: it consists of a temperature regulator (marked “poti” in the drawing), the 2 heating elements and a thermal fuse. See high-tech drawing above. Pizza goes between the two heating elements (I forgot to draw that).

Follow all the cables and check if they are not broken, disconnected or similar (simple) problems. Check that you have connectivity between the wall plug and the ovens interior, somebody might have broken the cord (i.e., by tripping over it).

All ok? I thought so. Next step!

Step

Check the heating elements

Next, we verify that the heating elements didn’t burn-out. Heating elements are super simple: they have a certain (small) resistance and can sustain high currents without burning. This means you can apply some voltage to them and they heat up. Thus, we can check them: if they have a infinite or zero resistance, they are broken. In that case you can trash the oven (unless you manage to find a replacement of course). If they work, they should show a small resistance as shown in the picture (26 Ohms sound about right).

Step

Check the fuse

If the heating elements are ok, it’s time to check the fuse. It’s usually attached close to the inner casing of the oven, and hidden in a layer of non-conductive heat-resitant tubing. The picture shows what it looks like. Test the fuse, if there’s no conductivity it’s broken.

Step

Replace the fuse

To replace the fuse, read the model number of the fuse. In my case, it said:

MICROTEMP
STGAHP
G4A00
TF 240C

Checking on the web, I’ve found the producer and the datasheet. With the datasheet, we can decipher the model number: It’s a 10A, 250V fuse for 240° Celsius.

These are quite common, I’ve found this part at the local electronics store for 2 bucks. Replace the fuse and voila, your oven should work again!

A note on replacing the fuse: as you can’t solder or use anything with plastic, the connections in such an oven are usually crimped. If you can’t manage to open the existing crimp-connector or have the part available, you can replace it with the metal part from a screw terminal (see picture). Just remember to strip off the plastic!