{"id":412,"date":"2018-07-29T10:24:44","date_gmt":"2018-07-29T09:24:44","guid":{"rendered":"https:\/\/www.burningimage.net\/cattrack\/?p=412"},"modified":"2023-07-22T07:56:57","modified_gmt":"2023-07-22T06:56:57","slug":"complete-build-summary","status":"publish","type":"post","link":"https:\/\/www.burningimage.net\/cattrack\/complete-build-summary\/","title":{"rendered":"tl;dr complete version 1 build summary"},"content":{"rendered":"

There are a lot of posts to trawl through in this blog if you’ve not followed it from the beginning. Hopefully this summary makes everything a bit clearer…<\/p>\n

The first thing I did was to have a look at other cat tracking products on the market<\/a>.  I found that they all have a big flaw… battery life.  I wanted GPS level accuracy and a battery life measured in months.  Nothing on the market offered that, so it was down to me to design it!<\/p>\n

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I quickly ruled out a constant cellular connection<\/a>, favouring a narrow-band RF design that spends the majority of its time in a deep sleep mode.<\/p>\n

Next was to look at the main building blocks of the design<\/a>, the GPS module, microcontroller and RF transceiver.  I had a think about how which communication protocols would tie everything together.<\/p>\n

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Once I’d worked out the main elements of the design, I needed to start choosing components.  First was the microcontroller.  I knew it’d be a PIC as I’ve a lot of experience working with them, but which one?!  I looked into the PICs that were available, and explained why you should never buy a PIC 16F84<\/a>!<\/p>\n

Now the microcontroller had been chosen, I needed a GPS module.  I looked at several small GPS modules<\/a>, before settling on an OriginGPS module – the smallest module on the market with an integrated antenna.<\/p>\n

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Then it was time for the last building block in the design, the RF transceiver.  I looked at Bluetooth 2\/3, Bluetooth 4, LORA, and raw FSK<\/a>, before settling on FSK and a transceiver IC from TI, chosen simply because it has the highest FSK sensitivity on the market.<\/p>\n

Next task was to choose a power source<\/a>.  I examined the current consumption of all the elements in the design, before looking for suitable batteries to power it.<\/p>\n

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The final part of the design was the antenna<\/a>.  Clearly I couldn’t have had a huge monopole antenna sticking up from Button’s head.  I needed something small and discrete.  I looked at TI’s excellent antenna design guide and went into some antenna theory and touched on antenna matching<\/a>.<\/p>\n

Before getting to work on the schematic I had to be clear how the collar was going to work:<\/p>\n

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  1. The collar initially sits in a ultra-low-power saving mode, waiting to receive a message from the basestation via the narrow-band transceiver.<\/li>\n
  2. The user sends a message from the basestation to the collar, requesting the cat\u2019s current GPS position.<\/li>\n
  3. The collar receives this message and instructs the GPS module to turn on.<\/li>\n
  4. As soon as the collar has a GPS fix, it sends the location information back to the basestation, using the narrow-band transceiver.<\/li>\n
  5. The collar then switches back to its ultra-low-power saving mode.<\/li>\n<\/ol>\n

    Now that I’d selected all my components, it was time to draw the schematic<\/a>.<\/p>\n

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    I examined the various parts of the schematic, explaining in detail what each element was responsible for<\/a>.<\/p>\n

    I spent many days looking for an enclosure that would fit on Buttons’ collar.  I eventually found one made by Hammond.  Once I had the enclosure, I could design the PCB<\/a> to fit it.  I was using my favourite design tool, Eagle.<\/p>\n

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    Whilst waiting for the PCBs to arrive I got on with writing the code<\/a>.  I thought about the different operation modes, the format of the packets I was transmitting and how I would encrypt the data and prevent RF replay attacks.<\/p>\n

    After a few weeks’ waiting, the PCBs finally arrived!  It was finally time to solder them!  This post<\/a> also goes into detail on matching the antenna, with lots of pretty pictures.  I also got to use my new microscope!<\/p>\n

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    Obviously I’ve not yet designed the basestation, but I could test the collar using a TI development board to simulate the basestation, so that’s what I did.  And guess what… it worked!!<\/a><\/p>\n

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    I could see the collar position arriving, encoded, back at the TI development board!  This post<\/a> also goes into detail looking at the RF protocol and what each transmitted byte means.<\/p>\n

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    So far I’d written all of my PIC code using the (non-free) CCS PIC compiler.  I wondered just how much bigger my code would be if I ported it to Microchip’s free compiler.  The result was a bit of a surprise<\/a>!<\/p>\n

    The time had come to replace the TI development board that I’d been using to talk to the collar with a properly designed basestation.  I had to think about how the basestation would be powered and how I’d use it day-to-day.  It obviously needed to have a screen and some buttons for user-input, but I also wanted to be able to communicate with the basestation remotely, from my PC.  Read all about the design here<\/a>.<\/p>\n

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    Naturally, the next thing to design is the basestation PCB<\/a>.  During this design I also had to think about what to do when it’s impractical to implement 50 ohm track widths.<\/p>\n

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    Once again, after a couple of weeks waiting by the letter box, the PCBs finally arrived and it was time to solder them<\/a>! The only thing I was missing was the LCD display, as eBay China had let me down (who’d have thought…).  I ended up ordering one from a supplier I trust – SparkFun.<\/p>\n

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    In writing the code for the basestation I learnt a lot about using the CC1125 transceiver for long range communications.  I initially thought that there was something wrong in my design, but it turned out to be a clock accuracy issue.  Read all about it, along with some RF theory regarding long range communications using the CC1125 transceiver<\/a>.<\/p>\n

    And after all that….. everything is working<\/a>!!<\/p>\n

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