[Halld-cal] Pulsing and bias for monitoring system

[Elton Smith]

Dear collaborators,

Attached is a conceptual schematic for the distribution of bias, power 
and triggers which need to be fed to each control board located on each 
end of the Bcal module. Connectors are represented with rectangles and 
ground connections are assumed but not drawn.

We assume that the cable connections from the Bcal readout assembly (and 
therefore the monitoring control board) will be connected to a 
distribution panel (or box) located close by at the end of the magnet. 
The cable contains one bias, one power and 4 trigger signals, one to 
fire each of the LED strings attached to the end of the module. The 
distribution box handles one quadrant on each end of the detector, i.e. 
there are 2x4 distribution boxes to feed the Bcal modules. The concept 
assumes that a single input of power, bias and 4 trigger signals will be 
supplied to all the 12  modules connected to this distribution box.

For +5V power and bias to the LEDs, we assume we will use the same 
modules that were purchased for the SiPM system (wiener MPOD 8008L 
and/or ISEG EHS F 205 PF). Each module has 8 outputs, so each output can 
feed one distribution box. We need to find the best way to break out the 
connector (with 8 voltage lines) and send them to the distribution box 
located on the detector near the end of the modules. In the drawing this 
is noted as a "custom" distribution. It could be a box with connections, 
or simply custom cable assemblies that take the 8 bias outputs from one 
connector and 8 power connections from the second connector and split 
out one bias and one power output to feed one distribution box.

The trigger TTL signals should be generated computer control, although 
with only a few options. One should be able to turn the triggers on and 
off and set the pulsing frequency to match the monitoring application. 
The trick is to find an easy way to fanout the signals to the 8 
distribution boxes. The fanout system could be implemented with NIM 
modules. Unfortunately, the fanout modules only operate withing a range 
of +/-2.5 V, so conversion to TTL signals is needed unless the 
distribution box can do the conversion there. I am assuming that the 
trigger cables would be coax (e.g. RG-58 with LEMO connectors).

This general arrangement should also work for the Fcal with appropriate 
modifications for the difference in geometry.

We need to finalize this concept soon so any updates can be feed into 
the ETC change request. However, the explicit implementation can be 
researched over the next year before we actually purchase parts or 
implement the plan.

Thanks, Elton.

-- 
Elton Smith
Jefferson Lab MS 12H5
12000 Jefferson Ave
Postal Suite #16
Newport News, VA 23606
(757) 269-7625
(757) 269-6331 fax

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