  The stellar evolution theory of massive stars remains uncalibrated with
high-precision photometric observational data mainly due to a small number of
luminous stars that are monitored from space. Automated all-sky surveys have
revealed numerous variable stars but most of the luminous stars are often
overexposed. Targeted campaigns can improve the time base of photometric data
for those objects.
  The aim of this investigation is to study the variability of luminous stars
at different timescales in young open clusters and OB associations.
  We monitored 22 open clusters and associations from 2011 to 2013 using a
0.25-m telescope. Variable stars were detected by comparing the overall
light-curve scatter with measurement uncertainties. Variability was analysed by
the light curve feature extraction tool FATS. Periods of pulsating stars were
determined using the discrete Fourier transform code SigSpec. We then
classified the variable stars based on their pulsation periods and available
spectral information.
  We obtained light curves for more than 20000 sources of which 354 were found
to be variable. Amongst them we find 80 eclipsing binaries, 31 $\alpha$ Cyg, 13
$\beta$ Cep, 62 Be, 16 slowly pulsating B, 7 Cepheid, 1 $\gamma$ Doradus, 3
Wolf-Rayet and 63 late-type variable stars. Up to 55% of these stars are
potential new discoveries as they are not present in the Variable Star Index
(VSX) database. We find the cluster membership fraction for variable stars to
be 13% with an upper limit of 35%.
