Customer Happiness Check-In

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 plant key:

genovese basil parsley sweet basil stevia stevia lettuce
genovese basil thyme sweet basil stevia stevia kale

 YIPPEE! I’m seeing growth in all but one of the stevia.  Maybe it is a late bloomer.  Curiously, I have the same feeling for the stevia being a late bloomer as I had when one of my kids took a long time to figure out how to walk.  Too good at rolling to bother :-).

Schematic for the Grow Chamber Sensor Puck 

I haven’t spent time working on the Grow Chamber sensor puck so I’ll put some time into it now.  But first…

Thanks To Those That Went Before

The Kicad Team – The KiCad EDA has come a long way.  KiCad has enabled so many of us to get into designing and building our own PCBs.  The team that does this work is amazing.  THANK YOU.

Contextual Electronics – Thanks to Chris Gammell’s Contextual Electronics, I have the confidence and ability to design and build PCBs.  Since I knew nothing about electronics before Contextual Electronics – after all, it is not something a woman in my age group would be encouraged to do – it is hard to describe the feeling of happiness I have in being able to design my own circuits.  THANK YOU.

ams and Silicon Labs – Both ams (manufacturer of the CCS811) and Silicon Labs (manufacturer of the Si7006) provided schematics which made it far easier for me to layout a schematic.  THANK YOU.

Open Source

The Kicad schematic I discuss below is located at this GitHub location.

The Schematic

The sensor puck will monitor CO2, temperature, and humidity.  To do this, I will use two chips:

Both use a VDD of between 1.8V and 3.6V.

The first thing I am doing is upgrading Kicad.  It has been awhile since I have used Kicad.  The current Mac version I am running is 4.0.3.  The version on the OS X downloads page is currently 4.0.5.  There is both a main package and an extras.  I just downloaded the main package for now.

I’m going to start a schematic that is only one page.  I do not see the need to have a hierarchical structure.  To lay out the CCS811, I’ll use the schematic in the CCS811 ams Eval Kit Manual (I copied the PDF to this GitHub location).

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Hmmm…one thing I didn’t see on this schematic were 10K pull-up resistors on the SDA and SCL lines.  I’ll add these.

I’ll use the schematic in the Si7006 data sheet for the layout of the Si7006 chip.

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Creating a schematic is a great way to get a deeper knowledge of the chip.  I am grateful for the schematics provided in the data sheets.  They are a great jumping off point!

Stuff I’m doing on the schematic:

  • I copied the ADDR circuit which pulls this pin to GND using a 4K7 resistor.  From the pin assignment documented in the data sheet (I copied the data sheet to this GitHub location), when the ADDR is low, the I2C address is 0X5A.   When I write the firmware, I’ll use 0X5A as the I2C address.
  • I’ll wire the AUX, PWM, and SENSE in the same way these pins are wired in the above schematic.  I don’t think I will be using the optional chip ambient temperature sensing.  However, it is of little cost to add the two resistors so why not?
    • One of the resistors is an NTC thermistor.  Which one to use?  I am happy to see the eval kit’s BoM:
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Drat the NTC Thermistor is in a 0402-N package…tiny for my soldering abilities…sigh…well…the footprint of the CCS811 doesn’t seem any better so for at least now, I’ll use the NTC Thermistor listed in the BoM and assume reflow will be able to handle the 0402 size since I’m not convinced my hand soldering is up to the task.

The CCS811 notes several application notes.  Sadly, I couldn’t find a way to access them so I sent a not to ams support (emailing cs-americas@ams.com):

Hello ,

I have purchased CCS811 chips from digikey.  The data sheet notes the following application notes:NewImage
 
The links provided lead to 404 (page not found).  I tried to find them on the ams site but could not.
 
Could you please provide me links to these app notes (and any others available for the CCS811?
 
Thank you and kind regards,
Margaret.

I’m seeing an increased risk of using the CCS811.  The chips themselves have a lead time (Digikey has about a 3 month lead time), and I can’t get access to documentation ams says is available.  I need to keep an eye on that!

  • Layout the components in eeSchema
  • Get the components in line with requirements to use the BoM generator I created awhile back.  From this blog post, two properties are used by the python program that will generate the BoM from eeSchema info:
    • Component Value
    • Part Number (labeled as PN).  The PN can be one of three things:
      • manufacturer’s part number.
      • Digikey part number
      • a “jellybean” part number.  Looking at the block diagram in the blog post, Jellybean parts exist in the JellyBeanPartNumbers.csv file.  I generate this CSV file from a google spreadsheet.  I have shared the one I’ve been using here.

I added the digikey PN to the CCS811 component:

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I populated the Value and PN fields for each component in eeSchema.

The current Schematic the only thing missing is a connector:

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And…well, I truly enjoyed my time spent in eeSchema.  That’s it for today!

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