Tag Archives: Wolverine Chip

Week 15: Moo 2.0 PCB Design

Last week, I met with Noah to review some last minute schematic changes that we had discussed before beginning the PCB design process.  He suggested that I move towards using the ADXL362 digital accelerometer in place of the analog ADXL330 on the current Moo. While the digital accelerometer may be slightly more complex to set-up in software, I would have to agree with Noah that this move is worth making.  Attached are the datasheets for both the ADXL330 and the ADXL362.

ADXL330 Datasheet

ADXL362 Datasheet

Pros of ADXL362:

  • nearly 100x reduction in active mode current consumption (~2uA at 2.0 V supply)
  • digital SPI interface.  Less susceptible to RF noise.  Our current Accel data is pretty noisy.
  • built-in digital temperature sensor
  • smaller package (3mm x 3.25mm x 1.25 mm)
  • user selectable measurement ranges (+/- 2g, 4g, 8g)
  • will be used on the Wisp 5.0 design.
  • avoids issue associated with 1.2V reference voltage for ADC on the MCU
  • motion-detection interrupts above a certain threshold

Cons of ADXL362:

  • never used before = requires new firmware development
  • Digital accelerometers are more complex than analog ones.  May be more prone to bugs in software.
  • one less serial communication bus available for external SPI peripherals
  • changing multiple components (MCU and accelerometer) can potentially increase the chance of error in new design.

Moo 2.0 PCB Design

I have begun laying out the PCB board with the Wolverine chip.  I moved some of the existing components on the board (e.g external Flash memory) to make the routing with the new MCU easier to manage.  The layout process was slow at first, requiring a good understanding of what had been done already, but has gotten easier as time progressed.  I currently have about half the connections set-up with the new MCU and will continue to work on the remaining connections this week.  If we do decide to switch to using the new accelerometer then I will need to make a schematic/PCB component and swap out the existing accelerometer.  This shouldn’t be too difficult because the new accelerometer uses a pretty straightforward SPI interface along with some separate connections for I/O Power (use GPIO), interrupts (may ignore for now or connect with 0 ohm resistors to MCU), and ground.

Note about the power supply requirement on ADXL362: “The ADXL362 does not require any particular startup transient characteristics, except that it must always be started up from 0V. When the device is in operation, any time power is removed from the ADXL362, or falls below the operating voltage range, the supplies (VS, VDD I/O, and any bypass capacitors) must be discharged completely before power is reapplied. To enable supply discharge, it is recommended to power the device from a microcontroller GPIO, connect a shutdown discharge switch to the supply (Figure 47), or use a voltage regulator with a shutdown discharge feature,such as the ADP160.” – ADXL362 datasheet pp. 37

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Week 11: Moo 2.0 Schematic Modifications (cont.)

Roughly half of last week was spent working on the Moo 2.0 Schematic modifications and the other half was spent either on-site or in the lab experimenting with ways to improve the tag rate in mortar.  I will first discuss the status update on the concrete deployment project and go into some detail about the Moo 2.0 modifications.

Concrete Deployment Update

Monday morning, Mike and I went over to the house to deploy two additional Moos inside the 3rd course of the sidewall (Moos #29 and #214).  Both Moos were placed with the signal antenna sticking slightly out of the cinder block.  We found that we were able to get a pretty good tag rate with #214 both before and after the remaining wall got built up.  However, we struggled to get a reading from #29 even before more cinder blocks were laid on top.  This motivated us to research ways in which we can improve the tag rate inside wet mortar.  After obtaining a sample of wet mortar from the construction site, Mike and I ran some additional experiments in the lab to see if you could improve the communication inside mortar.  The following google doc summarizes our findings and observations from this experiment: Tin Foil & mortar experiment

Summary of experiment:

  • placing tin foil behind the full submerged moo with 4 inch air-gap improved the tag rate from 0 (no reading) to 16 tags/sec (max).  First time getting a reading from a completely submerged moo inside wet mortar!
  • not able to get a reading when tin foil was placed directly on top of the moo (i.e. no air-gap separation)
  • experiment yielded similar results when performed outdoors (with added ambient noise)

This prompted Denis to place two additional (super-capped) moos with tin foil surrounding the inner walls of the two adjacent (non-filled) cinder blocks on the 6th course of the sidewall.

The following day, Mike and I performed some additional experiments outside of the lab using a cinder block filled with wet sand and a sheet of tin foil placed halfway through hole as well as on the two adjacent openings (see picture below).  In this orientation with one moo antenna sticking out, we were able to get a tag rate of 19.5 tags/sec.

Image

Later that day, Mike, Denis, and I went back to the house to reposition the readers and map out the moo placement on the front wall.  While walking around with the reader and power cords inside my backpack (aka “Ghostbuster pack”) and my laptop in my hands, we were able to scan the moos one-by-one  inside the walls for signs of a tag rate.  We were able to successfully get a tag rate from the following moos

Rear wall: #23 (max rate of ~6), #17, #26

Note: we observed that the reader antennas performed best in certain orientations and at very specific positions against the wall.  Denis placed tape on the walls indicating their orientation.  Also, we noticed that certain antenna types worked best with certain moos.

Side wall: #25 (max ~40), #214 (max ~60), and #19 (stray moo)

We repositioned the readers to record #23, #25, and #214 with hopes of catching the curing process.

Update from Mike (on July 20, 2013 at around 1pm):

#214 had a reading of 1.2 tags/sec

#25 has no reading (last seen on 7/17 at 10:06pm)

#23 has a reading of 21.9

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Moo 2.0 Improvements Update
For the rest of the week, I continued to read through the MSP430 Book, Wolverine Datasheet and user guide as well as the F2618 user guide and datasheet to better understand how the MCU functions. I have continued to make modifications to following google doc (Schematic Design Notes) tracking my notes for easier reference later on. Below is a screen capture of the schematic as of this writing.

schematic_screenshot

I have placed the connections for power (AVss, DVss, gnd), the crystal oscillator (LFXIN and LFXOUT) along with their external load capacitors (see google doc), and the JTAG connections (TCK, TDO, TMS, TDI, RST, and TEST). Note: the TEST pin is used on the F5969 to enable the JTAG pins. This pin was not required on the F2618 because the MCU’s JTAG pins were dedicated (aka not shared with GPIO pins). We will have to modify the Program header board schematic to accommodate for this additional pin (see below).
Capture

As can be seen from the schematic, I still need to route the connections for Transmit, Receive from the RF circuit, ADC inputs (temp, accelerometer, etc.) and the supervisor interrupt.  I have begun contacting Jeremy Gummerson with questions regarding the old design as well as suggestions for the new one.

fram

Week 10: Moo 2.0 PCB Modifications

Moo 2.0 Progress

This past week was devoted to mapping out the PCB board (and corresponding circuit schematic) modifications that will need to be made for the next generation Moo: Moo 2.0.  This began with making a component of the Wolverine MCU (MSP430FR5969) 48-pin QFN package.  I created a schematic symbol for the MCU from the datasheet and used the component wizard in Altium 10 (virtual connect to CAEN machine) to generate the corresponding footprint from the dimensions indicated in the datasheet.

After creating the component and swapping out the existing MSP430F2618 64-pin PM component from the schematic, I have begun slowly making the corresponding connections with the rest of the circuit board.  While some of the connections are trivial (Vss, Vdd, etc.), several of the pins are defined and placed differently on the new MCU (ADC ports, crystal, etc.).  It is worth noting the main differences between the two MCUs and what modifications we will need to make to the board. I believe that updating the schematic as well as the firmware to operate on the new platform will be far more challenging than rerouting the physical traces on the PCB board and is more prone to error, as well.  I have created the following (on-going) google doc to keep track of the design changes for the Wolverine chip on a pin-by-pin basis.

https://docs.google.com/a/umich.edu/document/d/1rRBA1XpxaT4seM81XRfJAb8Zv6Ewgvq1EuYT6sRaCwk/edit

Next Steps for Moo 2.0

  • continue to read through Wolverine MCU user guide and datasheet and make appropriate modifications to PCB schematic
  • continue to read through MSP430 design basics for more info on how firmware/hardware works
  • Verify schematic operation with Denis, TI folks (?), and others
  • Begin placing and routing new MCU on board

Applications of current Moo 1.1

Detecting Human Motion via tag rate

One potential application for the current Moo devices is using the inherent drop in tag rate of the Moo devices in the presence of humans to detect motion in a room.  Essentially, if a human were to stand between the reader and Moo devices, the transmission rate would change (i.e. drop to zero), thus behaving almost as a binary sensor to determine whether a human being is present or not.  I ran a simple experiment to verify that the tag rate will indeed change (https://docs.google.com/a/umich.edu/document/d/1htijqlbp-M36Qd0hf9DxoLl7tm29m0e1s7DlHBi1jOA/edit) in the presence of a human.  Building on this idea, I also ran an experiment using multiple reader antennas and multiple Moos in a straight line to see if it is possible to track human movement in a particular direction.  This experiment was also documented (https://docs.google.com/a/umich.edu/document/d/1L3HcSI5A6K1BFru7CkutJnyPxbUT-ZbOi7nSuUgQATg/edit).  However, the results were less illuminating because it the multiple antennas made it difficult to isolate the attenuation from human presence).