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_Art_

Chirp Qs

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Hi :)

I’ve just some questions about Garmin Chirp beacon...

1) Does anyone know what the penalty is with regard to battery life for the GPS device if Chirp searching is left on full time?

2) Do geocache databases supplied to GPS units have some flag to indicate they have a Chirp with them so the user knows to activate searching?

3) For anyone who has actually placed one... Did you get the whole year out of the supplied battery?

Cheers

 

 

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1) Someone did an actual current draw test here a long while back.  Have no idea the thread name, but it would be worth it.

2) Look for the 'beacon' attribute.  Most of the time, that will indicate a Chirp is in use (but not always!)

3) Ping a member whose handle is msstrong.  He had about 8 of them out concurrently at one time.  Should give you a pretty good idea.

His profile is here >> https://www.geocaching.com/profile/?guid=a4cc6b62-0a4b-4b56-acb7-c6e0f745b6b2

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1) Not much. I leave my chirp searching always on and I don't see significant less battery life.

2) Chirp caches must have the attribute "Wireless Beacon". Also it must be mentioned in the listing. Chirp caches are usually unknown or multi caches.

3) More than one year. My chirp cache is placed in 2014 and I only had to change the battery once until now (last summer).

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3 hours ago, _Art_ said:

Hi :)

I’ve just some questions about Garmin Chirp beacon...

1) Does anyone know what the penalty is with regard to battery life for the GPS device if Chirp searching is left on full time?

2) Do geocache databases supplied to GPS units have some flag to indicate they have a Chirp with them so the user knows to activate searching?

3) For anyone who has actually placed one... Did you get the whole year out of the supplied battery?

Cheers

 

1) Leaving Search on: Since I own Chirp devices, I don't leave Chirp Search on. Otherwise, I get notifications to my notifications :lol:. So I didn't compare battery drain.

 

2) Chirps in the database: I used the “Wireless Beacon” attribute for mine. This may or may not help you. I've considered placing a Chirp along a trail nowhere near the cache, and providing no waypoint. You just have to walk trails (no need to bushwhack at all), to perhaps discover it by chance one day. Don't worry, I never did that. But I'd like to anyway, if I think of the perfect way to set it up. B)

 

3) One year battery:  This depends on the battery and the Chirp. Inconsistency in manufacturing of both means the battery can leak at any time, and a Chirp having a low signal may become very bad too soon. Due to intensely humid summer heat and some ice in winter, I changed batteries every 6 months. No way I'm waiting for it to “go dead”. Actually, I swapped Chirps, not just the batteries, so the one in the field can be dried and cleaned up, to swap it back next time.

 

 

Edited by kunarion

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45 minutes ago, kunarion said:

 

1) Leaving Search on: Since I own Chirp devices, I don't leave Chirp Search on. Otherwise, I get notifications to my notifications :lol:. So I didn't compare battery drain.

 

2) Chirps in the database: I used the “Wireless Beacon” attribute for mine. This may or may not help you. I've considered placing a Chirp along a trail nowhere near the cache, and providing no waypoint. You just have to walk trails (no need to bushwhack at all), to perhaps discover it by chance one day. Don't worry, I never did that. But I'd like to anyway, if I think of the perfect way to set it up. B)

 

3) One year battery:  This depends on the battery and the Chirp. Inconsistency in manufacturing of both means the battery can leak at any time, and a Chirp having a low signal may become very bad too soon. Due to intensely humid summer heat and some ice in winter, I changed batteries every 6 months. No way I'm waiting for it to “go dead”. Actually, I swapped Chirps, not just the batteries, so the one in the field can be dried and cleaned up, to swap it back next time.

 

 

 

I like how you think 8^)

 

I have multiple chirp devices, but it never occurred to me to measure the mA draw chirp searching consumes.... Maybe when I do the next test...

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12 hours ago, _Art_ said:

Hi :)

I’ve just some questions about Garmin Chirp beacon...

1) Does anyone know what the penalty is with regard to battery life for the GPS device if Chirp searching is left on full time?

2) Do geocache databases supplied to GPS units have some flag to indicate they have a Chirp with them so the user knows to activate searching?

3) For anyone who has actually placed one... Did you get the whole year out of the supplied battery?

Cheers

 

 

 

1. I tested tonight my GPSMAP 66, and found that enabling chirp searching increased power consumption by less than 10mA.

2. As others have noted, chirp caches are supposed to include the 'Wireless beacon' attribute. Currently, Garmin GPSr do not display any attribute information.

3. I typically see more than 12 months battery life, but I do not use the cheap 2013 batteries you get at the dollar store either.

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Thanks for the replies :) 

 

Atlas, do you have a rough figure for current draw with backlight off in usual operation?

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5 hours ago, _Art_ said:

Thanks for the replies :) 

 

Atlas, do you have a rough figure for current draw with backlight off in usual operation?

 

Yes, the lowest consumption I have measured on my 66, with back light off, Wi-Fi off, Bluetooth off, GPS only, Compass on, menu screen displayed, is about 90mA. 

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Ok, I’ve mounted it, and externally powered it without breaking it so far :D

https://imgur.com/a/eC7Au6t

 

The only hairy part is coming up. Breaking out the SPI interface between the microcontroller and transceiver chip to read it.

Wish me luck! :D I got two of them in case of ruining one, but I’d rather keep the second chirp intact.

 

I swear they called the whole thing Ant because of the two antenna pins.

https://imgur.com/a/VGlWpEN

 

.... and... four connections can’t be made across one side of the chip because the insulation won’t fit!

I’ll have to stagger connections between both chips on the SPI bus. I didn’t foresee that one!

https://imgur.com/a/oUvrj21

 

Edited by _Art_

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Still works!

https://imgur.com/a/rAxqpU1

 

All good from here I think. The third wire has a PCB via I can scrape the coating off, and use.

The fourth wire is for the last pin on the side of the chip, so I can lead the wire in sideways.

I’ll probably need a blob of potting compound to drop over it when done... before something breaks.

 

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As far as I’m aware, nobody has looked at it, so anything I find out is new.

 

Here’s the still working chirp with exposed SPI interface. This also has a temporary PCB to test what is done so far.

It lowers the voltage of one of the SPI data channels, and then mixes them both  together with diodes so both data channels can be seen on one channel of a scope.

One channel will be of lower amplitude than the other, so easily distinguishable which channel is which (which direction data is flowing),

but both SPI data channels only using a single scope channel.

 

https://imgur.com/a/xpZFHbr

 

When I’m done with that, my own microcontroller (dsPic) daughterboard will go there.

Edited by _Art_

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So far that there’s a quick burst of activity on the bus every 2 seconds whether a device is searching for it or not.

 

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1 hour ago, _Art_ said:

So far that there’s a quick burst of activity on the bus every 2 seconds whether a device is searching for it or not.

 

 

It must be "on" and receiving at all times, at least in short bursts.  Upon receiving an identifiable signal, then it would transmit.  That's what would use the most power, transmitting.

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Seems like my GPSr always need ~30 seconds to find an active chirp so I always assumed maybe twice a minute it was listening....

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The 64st only takes a few seconds from turning chirp search on, to find the chirp, then another 6 or so seconds to read in it’s info.

 

Most modern microcontrollers have low power sleep modes that are set to wake on desired events such as interrupts, or expiry of a timer.

In this case both chips have. The transceiver probably wakes up when it’s selected with it’s enable pin.

 

If only my scope had SPI decoding, I’d see the packets now, but unfortunately it will take me some more building and programming to get another microcontroller to do it.

 

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11 hours ago, _Art_ said:

So far that there’s a quick burst of activity on the bus every 2 seconds whether a device is searching for it or not.

 

Am curious... what kind of bitrate are you seeing over the SPI?

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I’d say it’s the fastest the chips can do so that it can do it’s business quickly and go back to sleep. Maybe about a 10MHz SPI clock.

I see activity on my scope, but it has issues with waveforms at that speed. I’ve also got LEDs on both data channels, and they make things more obvious.

 

I totally forgot this thing has the transmit half of a serial port. It does output data, so I might as well go for the easy part first.

 

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Guess what would be nice would be the equivalent of Wireshark for SPI that could make your life easier.  Sniffing a totally unknown protocol  is a drag, but it's sure a lot easier with the right tools.

 

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I don’t expect much from it other than seeing valid data. I expect that to be encrypted though. Garmin wouldn’t want clones to be easily made.

Since the GPSr sends the timestamp and serial number, I’d be using both of those to encrypt the rest of the transaction if it were me making it.

It’s possible the timestamp and serial number will be in the clear, but they could also have some obfuscation known by the GPSr and Ant device.

 

The serial was boring. While the Chirp is idle, it outputs “0xE0, 0x00” bytes every two seconds at 4800 baud 8N1.

While transmitting to a GPSr, there’s a few more byte values in there, but none of it has any meaning in ASCII.

 

 

 

Edited by _Art_

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WLSoft easily created an Chirp app for Android  so I guess it wouldn't be too hard to decrypt. Maybe you can contact the maker of the app, his contact information is at the bottom of the page.

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I suspect that the Ant support and the dongles do the encryption, and provide access to use it through an API.

Being able to write an App doesn’t mean the author is privy to that kind of information, but it’s worth a shot.

 

EDIT,

I send an email and got a reply. It’s used through an API that wouldn’t provide access to encryption (that I’m assuming to be employed).

Basically, for an example, anyone can write an iPhone App that plays music form the user’s library, but you can never see inside the music file,

extract data from it, see frequency values to write a spectrum display, or anything else to access the music files. You basically get a list of songs,

and tell the iPhone to play one of them. Not even Apple can access the actual data (I suspect) or their own music App would have a spectrum display.

 

 

 

Edited by _Art_

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Hi :)

 

A bit of an update. Never mind the terrible ringing on the scope traces... my scope probe there was just wires & alligator clips,

but here’s an example SPI byte transmitted (I forget which direction this is relative to the mcu & RF transceiver).

Scope SPI:
https://imgur.com/a/QpYJKQP

 

Too fast for software SPI functions, and I need one hardware SPI module for an SD card eventually, so I decided to make a third hardware SPI peripheral for the dsPic with two shift registers.

This image shows the last byte in whatever packet was being transmitted on the row of eight white LEDs.

Hardware SPI:
https://imgur.com/a/u6dxQQu

 

This allows my mcu SPI routine to read faster because the shift register hardware takes care of bit banging, and I only have to read in parallel bytes for that channel.

The structure so far:

Chirp Structure:
https://imgur.com/a/JY0otbC

 

Cheers.

 

 

Edited by _Art_

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Funny to see how you put your components to the wrong side of the breadboard :D I used to make a "SMD" PCB same way by using DIP-cases soldered to pads without holes over 30 years ago. Have you tried to find source code for ANT+ libraries? Android code is at least partially open source. 

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HI, I’ve done a little research, but was mainly bothered about hardware until about now.

The low level RF communication I expect to be abstracted away by the OS, and the fellow who wrote that App linked above alluded to the same.

It would be lucky for a proprietary thing like that to be out in the open.

 

If it were full understood, my goal would probably be to replace the message, and make that dynamic, like the current temperature or something.

 

So far what I can do is read in either SPI channel up to 8000 bytes (which is probably a number of complete transactions), and spit that out again

slowly and Human readable, from a serial port to read on a terminal, or a file on SD card or something like that. The serial terminal is the easiest bet right now.

 

 

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When reverse engineering something like this I would be interested if the message is the same every time. At least you could record all suitable messages and replay them.

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I assume both the time stamp and GPSr serial number are used as part of the key. The timestamp for the current visit is displayed int he chirp information screen.

 

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