V1666 Cyg is a SRA carbon star with a period of 376d and an amplitude of 10.9-12.9V. According to Alksne, Alksnis, Dzervitis: Properties of Galactic Carbon Stars, 1991 a secondary variability component exists. So far so good. My first observations around JD 2450490 till 2452200 matching good to this data.
Unfortunately I can not observe variable stars during the next years. Later I am starting again and try V1666 Cyg two times. But it seems that the star only shows slight variations. Therefore I was not sure whether I should start with V1666 agian or not.
The third time I look at V1666 the variable was fainther as I ever has seen it. Therefore I put V1666 on my list again and was very surprised about what happens now. Please be aware by looking at my observations that I have used different sequences and look at my comments about the first minimum (was around 14mag).
So far so nice! But now V1666 Cyg was to faint for my instrument. I ask for help from someone who can carry one my observations to see how faint V1666 Cyg will get. A cart is available but only with comp. stars up to 14.4 mag.
Because V1666 Cyg is a carbon stars this behavior may is connected with some kind of dust shell like CW Leo or RW LMi. Maybe therefore V1666 Cyg is also interesting for spectral analysis.