SMA PLT FLIES AT INCORRECT ALT FOR VFR FLT.

Narrative

I HAD FLOWN TO A SMALL AIRSTRIP; 830H; WHICH IS 3 NM ON 010 DEG RADIAL OFF THE DAYTON VOR FOR SCHEDULED MAINT. I FILED AND FLEW ON AN IFR FLT PLAN WHICH I NORMALLY DO AND PROBABLY DO 95% OF THE TIME THAT I FLY. THE TRIP BACK FROM 830H TO SOUTH BEND; IN; WAS RPTED EXCELLENT VFR CONDITIONS; SO I DEPARTED VFR; CLBED TO 6000 FT MSL SQUAWKING 1200. APPROX 30 MI SE OF FWA I CALLED APCH AND TOLD THEM MY INTENTIONS AND ALT. THEY GAVE ME A NEW SQUAWK CODE AND TOLD ME TO MAINTAIN VFR. AT APPROX 35 MI NW OF FWA I WAS TOLD TO CONTACT SBN APCH AND THAT THIS WAS A HDOF. I HAD PREVIOUSLY OBTAINED THE SBN ATIS AND WAS IN THE PROCESS OF SWITCHING FROM FWA TO SBN WHEN I SUDDENLY REALIZED I WAS AT AN IFR ALT. I IMMEDIATELY CLBED TO 6500 FT AND CONTACTED SBN APCH. I CONTINUED MY FLT IN A NORMAL AND AS USUAL MANNER AND LANDED AT SBN WHICH IS ALSO MY HOME BASE. I BELIEVE THAT BECAUSE I FILE AND FLY IFR MOST OF THE TIME; AND FURTHER BECAUSE I FLEW TO 830H EARLIER THAT DAY ON AN IFR FLT PLAN; THAT I HAD BECOME A CREATURE OF HABIT. HOWEVER; I BELIEVE THAT BECAUSE OF THIS INCIDENT I WILL NEVER FORGET IT. A LESSON LEARNED WELL.