  GRANDProto300 is the planned 300-antenna pathfinder array of the Giant Radio
Array for Neutrino Detection (GRAND), of which the first 100 detection units
have been already produced. Its main goal is to demonstrate the viability of
the detection of the radio emission from air showers initiated by inclined
ultra-high-energy cosmic rays with energies of $10^{16.5}$ to $10^{18.5}$ eV,
covering the purported transition region from their Galactic to extragalactic
origin. The front-end readout system of each detection unit of GRANDProto300
processes signals from the radio antenna and the particle detector, generates
the first-level trigger, and communicates with a central processing station.
Based on earlier designs, we have built the first prototype of this system
using two development boards and one self-designed front-end board. We present
our new design that is improved and more economical than the earlier one, as
well as test results and prospects for future work.
