With TESS and Kepler K2 light curve archive, 13 known $\delta$ Scuti stars were reanalyzed and a small region survey of 1 deg radius centered on V1821 Cyg in the open cluster NGC 26871 was carried out. We discovered 45 new variables which include: 11 eclipsing binaries with pulsating components, 9 $\gamma$ Doradus stars, 8 $\delta$ Scuti stars, and other types. AD Ari is now reclassified as an eclipsing binary. The strong beating caused by two close frequencies present in the $\delta$ Sct star CD-54 7154. We can resolve at least 53 pulsation frequencies in $\iota$ Boo. At the same time, V1821 Cyg, V2238 Cyg and other stars pulsate with a couple of dozen frequencies, which is a significant improvement from the previous ground photometry results of a few. In particular, K2 data greatly increased the number of pulsation frequencies of three $\delta$ Sct stars: BU and BV from six to 27, and BN Cnc from five to ten. EX Cnc is an enticing asteroseismic target for its three groups of pulsation frequencies. Only a few stars can exhibit rich and regular pulsation patterns in their frequency spectra. With high-precision and long-term space-borne photometry, we can discern the pulsational contents of these stars more clearly and enhance our knowledge of them. The true nature of a star’s variability can be revealed by advanced photometry. The current small survey deserves to be continued and further expanded. The H--R diagram using the largest amount of member stars shows both $\delta$ Scuti and $\gamma$ Doradus stars occupy almost the same region; this would suggest a united pulsation mechanism.