Assumptions: Cockcroft-Walton photomultiplier bases are the same for all ECAL sections Digital to analog converters are installed on the distribution boards Control distribution boards are the same for ECAL and HCAL Low voltage power supplies and distribution boards are located under the ECAL supporting platform Middle voltage power supplies ( V ) placed outside of detector area Control and signal cables are placed between module tubes vertically Horizontal gap between R/O housing is from 87,4 mm ( outermost region ) to 10 mm ( innermost region ) Number of channels in column is from 52 ( outermost region ) to 172 ( innermost region ) Control and signal cables are attached to the steel tape Minimal gap is 10 mm between end caps of the inner modules Maximal total thickness of cables is 9 mm ( 2 rows of the coaxial cables and 2 rows twist & flat cables ) Individual 2 pins connector for coaxial cable Individual 2 pins connector for DAC voltage Individual 10 pins connector for supply voltages Control and signal cables are attached to the steel tape Implementation of the mother board for the inner modules allows to decrease number of control wires approximately two times Individual 10 pins connector for DAC voltages of the inner modules; individual 2 pins connector for DAC voltage of the middle and outer modules Individual 2 pins connector for coaxial cable of the modules Individual 10 pins connector for supply voltages of the modules Possibility to supply voltage to the groups of channels ( 16 54 channels per group ) Using the R/O space of empty innermost channels to route cabling around beam plug Just 10 modified readout housings are needed for one half of ECAL Block diagram of 216-channels DAC board DAC board main characteristics: Readout of a real HV controlled voltage, Power consumption about 1.5 W, Printed board size about 160*250 mm 2. PROTECTION CHAIN MUX SPECS or EMBL interface ADC In Out VOLTAGES / CURRENT MONITOR POWER (SUPPLY VOLTAGES) READ / WRITE PROTECTION CHAINS STATUS CONNECTORS FOR POWER SUPPLY Middle voltage Remote switch ON Read status To CW bases group Relay 6N39 DAC Amp. MAX5250 DAC out Ground Return ground RiRi R feedback MAX4178 drives all DACs in groups Individual adjustment of channel is possible MAX4178 Wide Reference Current Dynamic Range Guaranteed 250nA to 2.5mA with 5% Monitor Accuracy Extended 10nA to 10mA with 10% Monitor Accuracy Current (MAX4007) or Voltage (MAX4008) Monitor Outputs Reference Current-Limit Protection (20mA, typ. ) Voltage Clamp Protects Subsequent Output Circuitry +2.7V to +76V Wide Voltage Range Operation 6-Pin SOT23 Packages To CW bases group Distributors are located under supporting platform Distributor has standard slow control card ( ELMB or SPECS ) and 255 DAC channels 12 distributors are controlling half of the ECAL Minimal length of flat control cables Power supplies Distributors and low voltage supplies are located in the rack under supporting platform Minimal number of slow control cards Minimal length of power buses Convenient access Design with digital to analog converter outside Cockcroft-Walton bases is possible. This approach has been successfully used for TestBeam 02 measurements ( DAC separated from CW bases by about 30 m ) Control distribution boards design could be identical for ECAL and HCAL Design of the control distribution board could implement basic elements ( protection chain, voltage monitoring and voltage drop correction ) used at HERA-B ECAL Further optimization is possible before final design of the HV system is established