This repository contains the KiCad schematics and design files for a 19″ backplane designed according to IEEE 1101.1-1998 to mount the laser electronics in the Eurocard form factor developed by APQ. See below for a list of compatible devices. The design files can be found on the releases page.
This repository contains the schematics for the APQ 19″ sub-rack backplanes to mount electronics within a 19″ rack. The backplanes use several IEC 60603-2 C64AC connectors that can be configured to mount several different types of Eurocard devices used by this group. There is space for up to 6 connectors mountable in different positions to accommodate both the Fischer Elektronik HB ME 14 and the Fischer Elektronik TFP 3 14 system.
Compatible devices can be found here:
- Digital Controller for Laser Frequency Stabilization (RedPitaya-Lockbox)
- Digital Controller for Laser Intensity Stabilization (RedPitaya-IntStab)
- Ultra Low Noise Diode Laser Driver (DgDrive)
- Phase-Frequency Detector
- Modulation Transfer Spectroscopy (MTS) Module
- Multi-purpose OpAmp Circuit Board
- PDH Module
There is a datasheet available that lists the most important electrical and mechanical specifications. The latest version can be found here. Older version can be found attached to the respective release.
The backplane is designed to be mounted inside a 19″ sub-rack chassis. The most common systems used in this group are the Schroff EuropacPRO and the Fischer Elektronik BGT 384 180. Additionally a power supply must be provided. Typically, a rack mountable DC power supply like an HP 6632B is used for each rail.
- Torque screwdriver of size TX8, set to 0.3 Nm
- 1.3 mm screwdriver for hexagonal socket screws
- 3 U 19″ sub-rack chassis
- Schroff EuropacPRO or
- Fischer Elektronik BGT 384 180) and the following accessories:
- 2x Fischer Elektronik IST 84 3 mm isolation strips. These go between the chassis and the backplane.
- 1x Fischer Elektronik BGT 384/2 M2.5 mounting strips. A package contains for strips, two for each side of the chassis.
- 6x Fischer Elektronik FSC 160, one for each module installed.
- 1x optional Fischer Elektronik AB211 cover panel. These can be made of mild steel on special order for additional magnetic shielding compared to aluminium.
- Power supply with ±15 V outputs
- Power cable with a MSTB 2,5 HC/ 3-ST-5,08. See power cable assembly below for details.
- Up to 6 female straight IEC 60603-2 C64AC connectors depending on the number of devices to be installed. Use class 1 or 2 connectors for better longevity. Examples are ept 304-40054-01 via Farnell or Harting 09032646824 via RS or Mouser.
- 8x M2.5x8 DIN 914 / ISO 4027 set screws to fasten the Fischer Elektronik BGT 384/2 mounting strips
- 10x M2.5x10 ISO 14583 TX8 screws
- 10x M2.5 DIN 125-A / ISO 7089 plain washers
Important
Use a torque screwdriver (0.3 Nm) to tighten the screws holding the PCB, otherwise the PCB might flex and damage components.
- Start by soldering in the IEC 60603-2 connectors. There are markings on the PCB that show where to install these depending on the type of device enclosure used. Devices built around Fischer Elektronik HB ME 14 and Fischer Elektronik TFP 3 14 are supported.
- The backplane must be fixed to the subrack assembly by 5 equidistant M2.5x10 mm TX8 screws installed in each of the top and bottom row of mounting holes. Use the torque screwdriver set to 0.3 Nm to fasten the screws. Do not use a higher torque or the PCB might flex and damage the SMD ceramic capacitors. Do also remember to put the Fischer Elektronik IST 84 3 mm isolation strips between the backplane and the subrack if using a Fischer rack. Similar strips come with the Schroff EuropacPRO subracks as well. Otherwise the Eurocard modules will not fit.
- Once firmly installed, connect the power cable to the PCB and the power supply and set the the power supply to ±15 V without any devices inserted into the sub-rack. When the power supply is turned on, two green LEDs should light up to signal that the input voltage is of correct polarity and value.
- Turn off the power supply and insert the devices.
The board has a MSTBA 2,5 HC/ 3-G-5,08 header. The plug required on the cable side is a MSTB 2,5 HC/ 3-ST-5,08 Do note, there is an HC (16 A) and a non-HC (12 A) variant of the connector. The HC variant is required to meet the specifications. Typically, the other end of the cable features 4 mm connectors like the Stäubli LQ-4N-39 to connect to the DC power supply.
For low currents up to 5 A per rail (Note: This means 10 A combined on the common return rail) a LAPP ÖLFLEX CLASSIC 115 CY 3G1,5 shielded cable with 3 cores and 1.5 mm² wires can be used. For the full rated current a 2.5 mm² 3-core cable like a LAPP ÖLFLEX CLASSIC 115 CY 3G2,5 is required. The cables recommended do not have an inner sheath and are therefore lighter and more flexible than regular cables with an inner sheath. This is convenient for routing the cable inside the rack. The cables are not colour-coded, but rather use numbers printed on each of the black wires. Alternative cables that have an inner sheath are LAPP ÖLFLEX® CLASSIC 110 CY 3G2,5 (more rigid) and LAPP ÖLFLEX CLASSIC 100 CY 300/500V 3G2,5 (more rigid and colour-coded). The author does not have any affiliation with the Lapp Group and any other cable with similar specifications will work as well. The cables mentioned are meant as examples.
To assemble a cable proceed as follows to produce a cable with the dimensions shown below.
The backplane side, using a MSTB 2,5 HC/ 3-ST-5,08 connector, is straightforward:
- Cut back the outer sheath by 5 cm and remove it
- Trim the braid to about 1 cm and fold it back
- Put shrink tube over the braid and the cut
- Strip the three wires using a wire stripper
- Twist the cores
- Insert the wire labeled number 1 into position 1, the green/yellow wire then goes into the center, and the black wire labeled number 2 must be inserted into position 3
The 4 mm connectors for the DC power supply require more work because the common conductor needs to be spliced. The desired end result is:
- 4 connectors (red, blue, 2x black) on 15 cm wires
- 1 yellow connector on a 20 cm wire
To get there, do the following:
- Cut back the outer sheath by 15 cm and remove it
- Trim the braid to about 2 cm and solder an 18 cm yellow 1.5 mm² wire to it.
- Place shrink tube over the yellow solder joint
- Trim the center green/yellow conductor of the cabel to about 2 cm
- Solder two 13 cm 2.5 mm² wires to it and place black shrink tube over the solder joint.
- Place black shrink tube over the black splice of the common rail
- Place shrink tube over all wires
- Strip all five cores using a wire stripper,
- Twist the cores
- Solder the 4 mm connectors to the wires
Use a label maker and put a label stating the maximum current and voltage on the cable:
16 A/60 V maxif using an HC connector and 2.5 mm² cables12 A/60 V maxif using a non-HC connector or any 1.5 mm² cables (excluding the yellow cable connected to the braid)
The design files required for the PCB production and assembly can be found on the releases page and include the following resources:
- Schematics as a PDF
- Gerber files
- Pick & place position files
- Bill of materials as a CSV file and also as an interactive HTML version
The latest revision of those files can be found here.
Several variants of the design files are provided for the user. There is a so-called default variant, a HBME variant and a TFP variant.
The default variant does not contain any IEC 60603-2 connectors. This is the version sent to the boardhouse for assembly and it is the version that is found on new backplanes. It allows the user to customize the backplane for several different devices. Depending on the type of device used in the subrack, the IEC 60603-2 connector must be installed in a different position. This is discussed below.
This variant is an example where all slots are equipped with IEC 60603-2 connectors for devices that come in the Fischer Elektronik HB ME 14 form factor. These are fully shielded devices that come with an enclosure.
The TFP variant is used for devices utilizing the Fischer Elektronik TFP 3 14 assembly. These device have an open frame. The design files show an example configuration that uses IEC 60603-2 connectors considering a subrack full of TFP devices.
To work on the KiCad design files, a number of external libraries are needed. Those libraries show up as empty folders in the zip file, because they are not included in the release, but must be downloaded separately from the links given below. This can be avoided by checking out the whole repository using git. This way the libraries will be downloaded as well. Use the following command to clone the git repository along with the submodules using the --recurse-submodules flag.
git clone --recurse-submodules https://github.com/TU-Darmstadt-APQ/DIN_41612_Backplane.git
See the following repositories for more information as these are part of the design files.
I use SemVer for versioning. For the versions available, see the tags available for this repository.
- MAJOR versions in this context mean a breaking change to the external interface of the hardware like different connectors or functions.
- MINOR versions contain changes to the hardware that only affect the inner workings of the circuit, but otherwise the performance is unaffected.
- PATCH versions do not affect the schematics or invalidate older bill of materials. These changes may include updated components (to replace obsolete parts for example), an updated silkscreen, or fixed typos.
This work is released under the CERN-OHL-W See https://ohwr.org/cern_ohl_w_v2.pdf or the included LICENSE file for more information.