  We use the baryon acoustic oscillation (BAO) feature in the angular power
spectrum (APS) of the 21cm line of neutral hydrogen (HI) to constrain
cosmological parameters. As the BAO shift parameter can only constrain the
product of the Hubble constant and the sound horizon $H_0r_s$, we combine our
Fisher matrices with cosmic microwave background (CMB) Fisher matrices from the
covariance of $Planck$ telescope to break this degeneracy. In particular, we
find that the best constraints we can get with this method are on the Hubble
parameter $h$, and the dark energy parameters $w_0$ and $w_a$. Assuming a noise
level as for the BINGO telescope, we find $\sigma_h = 0.0055\;(0.8\%)$ in the
$\Lambda$CDM model. For the $w$CDM model, we find $\sigma_h = 0.020\;(2.9\%)$
and $\sigma_{w_0} = 0.075\;(7.5\%)$. In the CPL parameterization, we find
$\sigma_h = 0.029\;(4.4\%)$, $\sigma_{w_0} = 0.40\;(40\%)$, and $\sigma_{w_a} =
1.7$. Although these constraints improve those from $Planck$ alone, we observe
the BINGO data will be more significant for the $w$CDM model. We also observe
the constraints from the BAO only is not as strong as using the whole 21cm
angular power spectrum, but it is less susceptible to systematic effects.
