WHAT

Design of electronics crate

WHY

The extensive number of Roach boards, ADC/DAC boards, and IF boards needed to operate and readout the Mkids detectors for the MUSIC receiver instrument requires a logical and systematic approach in packaging and powering the readout electronics.

HOW

**** THE FOLLOWING DISCUSSION PERTAINS TO MUSIC INSTRUMENT’S ROACH CRATES ONLY ****

Approaching the interconnection and organization of the Roach electronics crate design from a “card-cage” modular viewpoint resulted in an efficient, well laid-out, and repeatable modular design. A rail system was designed that would allow insertion and extraction of the submodules. Each submodule consists of a Roach+ADC/DAC+IF boards, along with the necessary interconnecting coax cables, DC power wiring, LED indicators and switches and their associated wiring, and ribbon cable. A front panel was designed and laid out for cooling fans, SMA panel mount connectors, and LED indicators and switches. A Positronic male/female 8-position connector pair with floating contacts defines the power interface and location of the voltages and currents from the power supply crate to the submodules. The spacing of the mounting holes on the baseplate allow the Roach board and ADC/DAC board to be directly connected, while with the IF board it is necessary and convenient to use SMP blind-mate high-frequency connectors.

In addition, the holes around the ADC chips provide localized heatsinking to draw away the excessive thermal heat generated during the operation of these chips. Heatsinks are attached to the tops of the chips for additional cooling.


SMA to SMP FD (full detent) adapter: SM8807A.pdf 
SMA to SMP SBCM (smooth bore catcher’s mitt) adapter: SM8810.pdf 
SMP F/F adapter with EMI rings: SM2614.pdf 
heatsinks: Swiftech_MC14_Copper_BGA_Ramsinks.pdf

The off-the-shelf rack cabinet is made by Hammond Manufacturing. It is the model RCHS1901424, an 8U high, 19” wide, heavy duty table-top rack cabinet: RCHS1901424.pdf

Parts List for the Roach Electronics Crate: Roach_Electronics_Crate_Parts_List.pdf

Complete AutoCad drawing file for the Roach Electronics Crate: electronics_crate_1.dwg 
CAD views of the complete Roach Electronics Crate: 
Front: electronics_crate_front.pdf 
Rear: electronics_crate_rear.pdf

Listing of the machined parts for the Roach Electronics Crate; these are the AutoCad 3-D drawing, the AutoCad dimensional drawing, and the PDF dimensional drawing:


1. MUSIC_baseplate_3D.dwg 
MUSIC_baseplate_dim.dwg 
MUSIC_baseplate_dim.pdf
2. MUSIC_bottom_guide_3D.dwg 
MUSIC_bottom_guide_dim.dwg 
MUSIC_bottom_guide_dim.pdf
3. MUSIC_top_guide_3D.dwg 
MUSIC_top_guide_dim.dwg 
MUSIC_top_guide_dim.pdf
4. MUSIC_support_Positronic_female_3D.dwg 
MUSIC_support_Positronic_female_dim.dwg 
MUSIC_support_Positronic_female_dim.pdf
5. MUSIC_support_Positronic_male_3D.dwg 
MUSIC_support_Positronic_male_dim.dwg 
MUSIC_support_Positronic_male_dim.pdf
6. MUSIC_support_rail_1_3D.dwg 
MUSIC_support_rail_1_dim.dwg 
MUSIC_support_rail_1_dim.pdf
7. MUSIC_support_rail_2_3D.dwg 
MUSIC_support_rail_2_dim.dwg 
MUSIC_support_rail_2_dim.pdf
8. MUSIC_front_panel_3D.dwg 
MUSIC_front_panel_dim.dwg 
MUSIC_front_panel_dim.pdf 
The artwork for the front panel:

 MUSIC_front_panel_silkscreen.pdf

For the crate, the front panel is blank aluminum 0.125” thick Hammond Manufacturing PBPA19014BK2: PBPA19014.pdf 
This panel is machined with one large cutout to allow the 8 submodules to be passed through during insertion and extraction. Captive nuts are located on the edges so each submodule can be secured once installed into the crate. 
MUSIC_front_panel_8U_3D.dwg 
MUSIC_front_panel_8U_dim.dwg 
MUSIC_front_panel_8U_dim.pdf 
In the assembly of the crate, at the locations of the 6-32 flat screws, standard 6-32 washers are needed between the back of the front panel and the front faces of the top and bottom guides, due to the thickness of the industry-standard clip nut plates used along the left and right edges.

The two rear panels for the crate are steel 0.072” thick. 
The upper one is a prefabricated slotted 2U panel, for venting heat generated inside the crate to the outside. Supplied by Hammond Manufacturing, PVSS19003BK2: PVSS19003.pdf 
The lower one is a 6Ublank, Hammond Manufacturing PBPS19010BK2: PBPS19010.pdf 
This panel is machined with cutouts for the I/O connections to the Roach boards and with locations for the electrical connectors that interface to the power cables from the power supply crate. MUSIC_rear_panel_6U_3D.dwg 
MUSIC_rear_panel_6U_dim.dwg 
MUSIC_rear_panel_6U_dim.pdf
Views of the CAD models of the redesign of the ADC_DAC_Roach_IF boards and their interconnections, resulting in a more modular solution. Shown are the top and bottom guides, along with the Positronic male and female connectors and their support pieces, to location of the connectors for the proper electrical interface : 
ADC_DAC_Roach_IF_1.pdfADC_DAC_Roach_IF_2.pdfADC_DAC_Roach_IF_3.pdfADC_DAC_Roach_IF_4.pdf 
ADC_DAC_Roach_IF_5.pdf

Wiring diagram for one submodule, which consists of one Roach board, one ADC/DAC board, and one IF board, with two 40mmx40mm fans for cooling: Roach_Electronics_Crate_submodule_wiring.pdf 
Using a female Positronic connector, PLB08F2B0A1, a pigtail wiring harness can be assembled for applying power to a Roach crate submodule, for laboratory testing purposes on the benchtop. The proper connections, voltages and currents are: Power_connections_for_the_electronic_assemblies.pdf

Wiring diagram for the crate, showing the connections from the circular box mount connectors to the Positronic female connectors: 
Roach_Electronics_Crate_IF_wiring.pdf 
Roach_Electronics_Crate_Roach_wiring.pdfRoach_Electronics_Crate_ADC_DAC_wiring.pdf 
Roach_Electronics_Crate_fan_wiring.pdf