
\subsection{Frontend Electronics and Data Acquisition System}

The frontend electronics of the AlCap experiment includes; 1) A CAEN
time-to-digital converter (TDC) model V767 which reads the $\mu$PC and 
2) Several types of waveform digitisers (WFD) recording raw pulse
waveforms.  A 12-bit 250-MS/s CAEN digitiser model DT5720 was used to 
record fast pulses from the entrance muon counters (a thin plastic
scintillator $\mu$Sc to provide a time reference; a 
scintillator detector $\mu$ScA to veto muons from beam halo; and 
a thick scintillator detector to veto muons which did not stop in 
the target). 
A 14-bit 100-MS/s CAEN digitiser model V1724 was used to instrument 
the germanium detector.
 Custom-built 12-bit 170-MS/s flash analogue-to-digital converters
 (FADCs), 
previously used for the MuCap experiment, were used to instrument the 
neutron detector, all silicon detectors and the remaining 
scintillator detectors.

The germanium detector and all silicon detectors use two parallel readout channels.  
One channel has a very fast preamp shaping time, to be used for precise time resolution on the order of a few nanoseconds. The other channel uses a longer shaping time which results in a better energy resolution. 
The two readout channels are acquired and written to disk independently and recombined offline.  
For the scintillator detectors, which are just used for veto, a slow signal was not necessary so each was read out by a single channel.

To synchronise the different detectors, AlCap follows the approach 
successfully exploited by other muon experiments at PSI (MuCap and MuSun). 
The data collection is organised into $\sim100$-ms-long time segments
where the length of the time segments was optimised. 
During each segment, signals from all detectors are recorded
independently 
by threshold crossing and were time-stamped relative to the start of
the segment. 
The clock signals for all electronics modules are derived from a
common source, which allows us to time-correlate different detectors
in the offline analysis.  It also provides an opportunity to conduct 
various background studies, and exercise different veto selection conditions. 

The data acquisition system (DAQ) of the AlCap experiment is based on the MIDAS framework.
It provides the readout of the frontend electronics into data blocks, data logging, hardware monitoring and control, and the run database of the experiment.
Each data block (also known as a MIDAS block) contains data from all detectors from a given time segment. 
In R2013, the DAQ consisted of two frontend computers, one backend computer (which was also used to run several frontend processes), one slow control computer, and one computer for the offline data analysis. 




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