  Interstellar scintillation analysis of pulsars allows us to probe the
small-scale distribution and inhomogeneities of the ionized interstellar
medium.
  Our priority is to present the data set and the basic measurements of
scintillation parameters of pulsars employing long-term scintillation
observations carried out from 2011 January to 2020 August by the European
Pulsar Timing Array radio telescopes in the 21-cm and 11-cm bands.
Additionally, we aim to identify future possible lines of study using this
long-term scintillation dataset.
  We present the long-term time series of $\nu_{\rm d}$ and $\tau_{\rm d}$ for
13 pulsars. Sanity-checks and comparisons indicate that the scintillation
parameters of our work and previously published works are mostly consistent.
For two pulsars, PSRs~J1857+0943 and J1939+2134, we were able to obtain
measurements of the $\nu_{\rm d}$ at both bands, which allows us to derive the
time series of frequency scaling indices with a mean and a standard deviation
of 2.82$\pm$1.95 and 3.18$\pm$0.60, respectively. We found some interesting
features which will be studied in more detail in subsequent papers in this
series: (i) in the time series of PSR~J1939+2134, where the scintillation
bandwidth sharply increases or decreases associated with a sharp change of
dispersion measure; (ii) PSR~J0613$-$0200 and PSR~J0636+5126 show a strong
annual variation in the time series of the $\tau_{\rm d}$; (iii) PSR~J1939+2134
shows a weak anti-correlation between scintillation timescale and dispersion in
WSRT data.
