MDBT42Q Built in thermometer

[espruino-discuss]

Posted at 2021-08-17 by ingoiotESPruino

Hi,

I want a small data logger with only
the pure MDBT42Q, a CR2032 (or similar) and the built-in temperature sensor.
Is this sensor good enough for recording the room temperature every 15 min
(for about 7-14 days) without requiring particularly high precision, but it should not drift too much when the voltage drops.
Does the chip heat up too much to record the room temperature?
(Maybe even secured under glue)?

Or do I need something like a DS1820
Has the board enough power to drive this sensor?

[espruino-discuss]

Posted at 2021-08-18 by @gfwilliams

Hi,

Is this sensor good enough for recording the room temperature every 15 min without requiring particularly high precision, but it should not drift too much when the voltage drops.

It should be fine, yes. It won't drift, however you need to calibrate it first.

• So just measure the temperature with a device you trust, lets say it's 20 degrees C.
• Run var calib = 20 - E.getTemperature();
• Then whenever you read the temperature just do E.getTemperature()-calib

You only need to do that once per device. Otherwise it's fine.

Does the chip heat up too much to record the room temperature?

No, it should be fine in normal use. If you're doing BLE scanning or heavy calculation then maybe, but for doing something like recording room temperature you're good.

Or do I need something like a DS1820... Has the board enough power to drive this sensor?

You can use the DS18B20 with the MDBT42Q, but I don't think you need to. As above, the inbuilt one is probably fine

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Posted at 2021-08-18 by ingoiotESPruino

sounds good.

is there a way to find out/estimate how much space is left from the 512k flash to store
time/value pairs?

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Posted at 2021-08-19 by Robin

require("Storage").getFree()

http://www.espruino.com/Reference#l_Storage_getFree

Does process.memory() help?

http://www.espruino.com/Reference#t_l_process_memory

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Posted at 2021-08-19 by ingoiotESPruino

it does, tnx

as i havent got a MDBT42Q jet,
it would have been interesting how much much of the 512 kb flash is
left for logging - but i guesstimate its more than enough

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Posted at 2021-08-20 by @gfwilliams

Regardless of what Espruino device you have, require("Storage").getFree() should work fine.

There may be the odd bit of flash left outside storage on some builds, but the vast majority is usually in Storage