design a simple air filter for your automobile using the minimum parts and at the minimum price.
Always had a problem to stuffiness in the car in winters with windows rolled up. Great in summers too. works the year around if prefer driving with the windows up (keeps out the pollution :) )

Step 1: The Air Filter and Fan

you need a automotive air filter. i used one from a maruti suzuki ZEN (not zen estilo). Cost Rs.120/-. The filter has an outer rubber gasket which needs to be removed. The advantage of automotive filters is that they are economical, have large filter area (see the folded structure of the filter membrane), it traps the fine particles which cling to the filter membrane and do not brush off/drop off easily and the clean air that is good for your car engine is good for you :)

a 12v 4" DC fan. Cost Rs.200/-. use a normal speed or medium speed. the high speed ones would be very noisy (not much improvement in operation efficiency)

you can use any other filter type, mine was easy to fit with the fan. you could use a longer filter and install two fans side by side too

ps sorry for the old newspapers in the background, use them to protect my work table surface

Step 2: Joining the Fan and Filter

you need to place the fan on the filter such that the air flow is directed upwards (the fan operates in suction mode creating a vacuum which forces air to flow through the filter, its more efficient as the vacuum is assisted by the normal atmospheric pressure which forces air through the filter. if you blow air into the filter maximum air flows back due to the restricted flow from the filter membrane which reduces the fan efficiency)

Tack the fan on the filter using some instant glue (cyanoacrylate adhesive) (just to hold it in place) finish the job using a glue gun to form a strong bond

Hot Glue all four sides to prevent any air leakage

and you get the cured glue and joined fan and filter

Step 3: Final Assembly

take the rubber gasket and cut two sides out of it. need to use it for mounting support

glue each of the two on two the outer edges of the bottom of the filter (the side you wish to keep at the bottom) (the gaskets help the support the filter and provide an even level with the outer frame protruding from the filter edges)

take a 4"x7" laminate board for mounting the fan and filter unit. Cost Rs.10/-. Drill two 3mm holes for the mounting screws

Screw down the the laminate sheet. you'll need to work up the placement of the fan and filter on the laminate sheet as per the fixing space/mounting space available in your car

Step 4: The Finished Unit

The finished unit. I put in a protective fan grill for safety purposes (grill cost Rs.10/-)

view from the filter side

Two units for my two cars :)

I attached relimate connectors to the wire for easy electrical installation and removal

Step 5: Installed Unit

Installed it below the dashboard near the gear shift level. Fits snugly into it. Wire it to the ACC. (accessory) connection in the car (its provided through a fuse and the fan switches off when you remove the ignition key, the fan power consumption is just 200mA so no issue of battery drain if its on and car engine is off (until you leave it overnight, but who leaves his car with the key in overnight?))

when you switch it on you would hear a small hum of the fan operating which is not heard once you start the engine or switch in your music system :)

when the filter is dirty you can clean it using a high speed fan blower (can be cleaned 2-3 times before replacement) or to replace it just unscrew the two mounting screws and peel off the hot glue and glue and screw in a new filter. (one filter would easily last upto a year, then you can clean it and use it upto 6 months as required).