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We report an analysis of photometric behaviour of DI UMa, an extremely activedwarf nova. The observational campaign (completed in 2007) covers fivesuperoutbursts and four normal outbursts. We examined principal parameters ofthe system to understand peculiarities of DI UMa, and other active cataclysmicvariables. Based on precise photometric measurements, temporal light curvebehaviour, O-C analysis, and power spectrum analysis, we investigated physicalparameters of the system. We found that the period of the supercycle now equals31.45 +/-0.3 days. Observations during superoutbursts infer that the period ofsuperhumps equals P_sh = 0.055318(11) days (79.66 +/- 0.02 min). Duringquiescence, the light curve reveals a modulation of period P_orb = 0.054579(6)days (78.59 +/- 0.01 min), which we interpret as the orbital period of thebinary system. The values obtained allowed us to determine a fractional periodexcess of 1.35% +/- 0.02%, which is surprisingly small compared to the usualvalue for dwarf novae (2%-5%). A detailed O-C analysis was performed for twosuperoutbursts with the most comprehensive coverage. In both cases, we detectedan increase in the superhump period with a mean rate of dot_P/P_sh =4.4(1.0)*10^{-5}. Based on these measurements, we confirm that DI UMa isprobably a period bouncer, an old system that reached its period minimum a longtime ago, has a secondary that became a degenerate brown dwarf, the entiresystem evolving now toward longer periods. DI UMa is an extremely interestingobject because we know only one more active ER UMa star with similarcharacteristics (IX Dra).

Curious Variables Experiment (CURVE). CCD photometry of active dwarf nova DI UMa