Jan. 15, 2009 1Safety Board Review (Rev D)

Safety Board PCB Review(Rev D)

Eric Warmbier

Jan. 15, 2009Safety Board Review (Rev D) 2

Overview• Board is in use and well established, so the

functional details will be skipped.

• Safety Board needs a new layout– Current board has errors in design

• Modified via wire and additional components to this point

– Grounding / noise issues cause inadvertent (and annoying) watchdog errors

• Goal is to mainly look for errors in circuits on schematics and that all new features were added– Darryl and Eric will be responsible for looking over

signals and off board connections.

Jan. 15, 2009Safety Board Review (Rev D) 3

Documentation: Files & Format• There are 3 documents required for this review

– “TCS3-2070_Safety_Board_Schematics_Rev_C”• Original Rev B with hand wired modifications = Rev C

– “TCS3-2070_Safety_Board_Schematics_Rev_D”• New schematics for this review

– “Safety_Board_Rev_D_mathcad.pdf”• Equations explaining/documenting why value

Jan. 15, 2009Safety Board Review (Rev D) 4

Issues & ResolutionIssue Resolution

+/- 15V Comparator has -15V logic low output going directly in CPLD (it clamps).

Optocouplers perform logic level conversion.

Loading on comparator circuit circuits. Uneven +/- trip points.

Buffer amp and selecting correct resistor.

Loading on references. Changed design to use undivided reference.

Not enough test points, especially GND. Added many test points.

Mechanical support for board when inserting 50 pin connectors is too low.

Machine a plate.

(see slide on this issue)

Current board routing crosses digital / analog split. Design uses optocouplers. Not an issue now.

Names on schematic don’t indicate active low or high logic (George’s comment).

Good point. Signals should now indicate active logic level.

No watchdog timer on CPLD clock.

(clock gone = most error detection gone)

Add a watchdog timer to this clock.

Watchdog timers trip inadvertently. Optocouplers used to separate them. Currently in use at summit via small PCB & working.

No redundancy on brake relay control circuitry. Redundancy added.

Jan. 15, 2009Safety Board Review (Rev D) 5

Added FeaturesFeature Comment

On board push button for testing watchdog timers. Makes it easy to test.

Lab/summit selection jumpers are now switches, with a status to TCS3 software.

Won’t allow anybody to inadvertently install board up at summit in wrong configuration.

Added damped LC filters to board for power filtering.

Probably not necessary, but they’re there if needed.

Board will be laid out to allow for a cover that can be mounted to it with screws to the bottom plate.

Won’t initially make cover. It’s probably not required, but it’s available.

Trip points for comparators will have resistor paths or can use pots.

Resistors are preferred for signals that are almost never adjusted. Pots good for lab.

Additional power connector has more pins. IRTF PCB connector still installed in parallel.

Allows for 2 pins for each supply voltage. Reduces connection issues.

Mostly surface mount components used. Smaller, more available, etc. We also have complete resistor and cap kits for 1206 size.

Jan. 15, 2009Safety Board Review (Rev D) 6

50 pin 50 pin

16 pin

power

50 pin 50 pin

16 pin

power

Mechanical Mounting• General concept – not to scale or precisely drawn

Bottom Mounting Plate

(top view)

Optional Cover

(top view)

PCB

(top view)

Stack up(side view)

(bare copper)

(bare copper)