Idea for LimiTTer – it’s an idea how to make a device that reads the glucose data in the intra-oral fluid measured by the Abbott Freestyle Libre sensor and send it to the phone with the xDrip application. The xDrip application, which was created on November 15, 2014 and is developed by dozens of programmers as an open-source project to this day – was then and still is the most developed application “diabetic”. LimiTTer – as a new data source in this application used the transmission method and data format used by the Dexcom system.
Beginning September 2016, as soon as I became a user of the Libre system (which a few days earlier officially entered the Polish market) – I decided to adapt LimiTTer to our local conditions – mainly in terms of component availability, and perform it in a “service” way – for people who they can not make it themselves and program it themselves. The project received the name “Transmiter”.
In a short period of time – a few weeks there were 5 test transmitters, which were given to participants of the FB group – Freestyle Libre PL. The group formed not much earlier – in August 2016.
Operation and functions.
What is Transmiter? This is one of the most frequently asked questions on FB groups devoted to diabetes while discussing the Freestyle Libre system.
From the technical side – Transmiter is an NFC to BLE converter. Shortly, but few people will understand it, so a bit brighter:
the Freestyle Libre sensor can be read by the reader using the NFC protocol. This is the kind of data transmission that is used, for example, in bank cards for contactless payments. NFC requires that both devices that exchange data find you very close to a maximum of 1-2 cm from each other. With the Libre reader – we practically touch the sensor, either directly or through clothing.
If we do not touch the reader to the sensor – there is no way to find out what value it measured at the moment. That’s where the idea for LimiTTer and my modification or Transmiter came into being: this is a device that will be fixed all the time on the sensor and it will constantly transfer the measured results to the receiver – the phone. This “all the time” – of course, depending on your needs – the whole day, night, school stay, a few hours, etc. – who suits whom and what needs. And “continuous transmission” – this is sending the result every 5 minutes. The transmitter is powered by a built-in 240 mAh battery that lasts for 2-4 days of continuous operation. We load it – just like a phone, with the same charger as the Libre factory reader.
Summing up: LimiTTer / Transmiter – these are additional devices that form the fully-fledged system of continuous glucose monitoring (CGM – Continuous Glucose Monitoring) from the Freestyle Libre system. The minimum set is: Libre + Transmiter + Android phone and xDrip application. (and of course – plus the Libre factory reader to activate the sensor after it was installed).
- the ability to independently determine the time, what the measurement result is sent – in the range of 2 to 9 minutes. (currently – fixed time 5 minutes),
the option of selecting the transmission protocol – “old” – means sending only the latest measurement and “new” – sending all data, that is 15 measurements every 1 minute from the last 15 minutes and 32 measurements every 15 minutes from the last 8 hours.
- the possibility of measuring “on demand” – that is, after clicking the appropriate button / icon in the application. This function corresponds to the factory measurement with the Libre reader.
- completely new software that supports NFC sensor reading. This is the biggest change in the software, because it has been created virtually completely from scratch – with the main goal to remove “high” in measurements.
By default – all Transmitters II come out in the basic configuration, such as the current one, i.e. only the measurement every 5 minutes. Thus, they are fully compatible with the xDrip application.
Size limitations forced the change of power from the battery, which can be charged, to a replaceable CR2032 battery – which allows for several days of operation.