Region 3 Statuts Report


1) I2C related electronics

Undergraduate student Graham Giovanetti and I have designed some test board for controlling the MAD chip based front-end electronics.
The design of this electronics (schematics and layout) is part of Graham's honor thesis for Qweak
The layout has been send out to a PCB company (Advanced Circuits) which produced these professional looking boards:

Board #1 is an interface card which is hooked up to the parallel printer port of a compurt and provides an external I2C bus for communication.
Since the printer port does not provide much current for operating devices on the I2C bus, we added a power supply which uses a voltage regulator (+5V, LM 7805)
 


Most of the I2C and front-end electronics uses SMD parts (Surface Mounted Devices). We purchased some time ago a dual SMD soldering station
including desoldering tweezers for removing soldered components. Still waiting for the vacuum twezzers for picking up and placing the tiny parts on the boards.
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Board #2 is an I2C board for disabling/enabling individual wire signal on the input of theMAD chips. This is done by sending commands over I2C to the SMD chip
PCF8574 which proivides 8 programmable output pins wired later to the MAD chip. This board is equipped with 8 LEDs showing the status of the wire
(disabled input/ enabled input).



Board #3 is an I2C training board for reading and setting I2C data/commands. This board reads the temperature using an I2C temperature chip (+-0.5 deg resolution).
You can set the temperature (actually ADC) resolution and other parameters over I2C.
As you can see: most of the space is taken by the head post (flat ribbon cable plug) and the I2C chip address selector.


Installing some infrastructure for handling SMD based electronics. No, W&M does not have an electronics shop ...



And after some hours later:



2)  Front-End Electronics

All the 600 MAD chips have arrived. All of them have passed a electric pass/fail test provided by CAEN, means there are no burned or short-circuited chips
among them. The four containers are SMD kits for resistors and capacitors (SMD package sizes: 1206 and 0603), so we don't have to drive to JLab each time for a 2 cent part or to buy a reel with 5000 pieces
on it with for one value only.




William Gunning's first layout of the flexible Kapton board for transferring the wires from the wire frame to the front-end electronics.
We have chosen this "dual strip" design (2x8 channels) over a "single strip" design (1x16 channel), because it makes it easier to embedd
the flex-board into the wire frame (better o-ring gas sealing and simpler gluing procedure). The Kapton board consist of two layers,
one ground plane and a signal layer with as much grounding as possible. In addition I requested to implement a "two solder pad" design.
This provides a second chance to to solder the wire to the flex-board , in case the first pad peels off due to overheating while soldering.
Each strip has a SMD connector that will be plugged as close to the input pins of the MAD chips. We intend to use a stiffener for the
flex-board connectors in order to minimize damages to the Kapton  while (un)plugging the strips.
Betwen each signal strip is a grounded strip which minimizes cross-talk .
Anyway the design is not finalized, the pad locations and the signal routing are not optimized yet.
Bill Gunning is checking out different Flex-Board companies for sending out the revised design
(will receive 2 prototype flex-boards)

Pic below: Older version of the flex-board for transferring the wire through the wire frame to a 16-channel MAD board.


On Wednesday 05-03-06 Chris Cuevas, Bill Gunning, and I had another front-end electronics meeting. Main subject were the control options on a 16-channel MAD chip board
 Chris proposed to use a PIC16F877  (CMOS FLASH-based 8-bit microcontroller for ~$12) for each 16-channel board for handling all the above listed tasks. 
My concern is that any microcontroller needs a quarz oscillator (4-20MHz clock) for operation, which might cause serious problems with the very sensitice MAD chips
leading to oscillation due to pick-up noise. In addition it was not clear how radiation sensitive are those PICs ....
I proposed again the usage of an I2C bus (2 wire system). The advantage is that  the I2C bus is only active when you need to send/receive data and/or commands between measurements.
I2C does not require a constant clock on the bus like e.g. CANbus or other microcontroller accessed bus systems.  The advantage of the I2C bus is that it is dead/quiet during a measurement,
which minimizes any cross talk from I2C to the MAD chips. The I2C chips are quite simple compared to a microcontroller, therefore I2C chips should be less sensitive to radiation damages.
( INFN Italy used I2C bus/chips for controlling MAD boards at CERN w/o experiencing radiation damage related failures)
      
3) Flatness Scanner

Test setup for the flatness scanner. The flatness scanner is intended to measure height variation of the wire bridge, which defines the offset of the wire to a nominal wire plane.
In this setup the laser and receiver (photodiode) are both mounted on supports which is aligned and clamped on a precision granite surface table. The signal of the receiver is
amplified (small blue box to the right) and provides a DC voltage (10V max), depending on the quantity of light detected.
Sender and receiver (A-LAS 12/90 series) are purchased from Sensor Instruments for $1.2k .



      
                            Left: The laser with a profile of 3.0x0.75 mm (collimated)                           Right: The photodiode (4.0x1.0 mm)


The calibration of the light sensitivity will be done by placing precision gage blocks between laser and receiver. The higher the gage block, the more it blocks the light seem by the receiver, the less signal is measured
with a DVM. Initial tests suggest a sensitivity that easily allow to resolve a height variation of 25um.




4) Last but not least: Rotator Design and Geant4 Simulation


Paulo Medeiros is about to finalize the Rotator design and has sent out the drawings to four companies for starting the bidding process.
Hopefully we will stay within the budget of <$50k ...

One open issue: Are the rail sliders and/or the mounting plates+rods exposed to the ep-elastic envelope ?
According to Paulo's CAD ep-profile the vertical rods (right pic) are the closed objects to the ep-elastic envelope (~3inches).

=> Started to rebuild the Rotator geometry piece by piece in Geant4. So far it looks good, no scattering due to the ep-elastic envelope.  

http://dilbert.physics.wm.edu/elog/Software/239


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