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Slow VCC Rise Time

A project log for Low Cost Weather Station

Wireless weather station, powered by the sun and wind it intends to measure, below $50.

Ulf WinbergUlf Winberg 06/10/2015 at 11:480 Comments

When the weather station is powered by the sun and wind, the increase of VCC will be quite slow, while the capacitor is charged. This might cause the microprocessor to not start up properly, so I decided to test it.

There is reset circuitry built in to the BL600 to take care of such problems, but looking at the data sheet, it is not enough. A minimum rise time of 60 ms from 0 to 1.8 V is mentioned. Anyway I set out to test how bad it actually is by charging and discharging the capacitor 10 times, while observing if connection is made with my host computer. I have made a script to continuously try to make a connection, and I uploaded smartBASIC code I new worked well.

To my surprise, it worked every time (see below):

Started gatttool
2015-05-25 14:45:06.887746 Trying to connect (try nr 6)
Successfully Connected to Bluetooth Device
2015-05-25 14:46:18.124806 Battery level: 8 % (measurement nr 2)1)
2015-05-25 14:48:18.699739 Trying to connect (try nr 1)
Successfully Connected to Bluetooth Device
2015-05-25 14:49:35.850811 Battery level: 9 % (measurement nr 2)1)
2015-05-25 14:53:36.967842 Trying to connect (try nr 4)
Successfully Connected to Bluetooth Device
2015-05-25 14:56:09.792776 Battery level: 4 % (measurement nr 3)))
2015-05-25 15:01:31.447688 Trying to connect (try nr 6)
Successfully Connected to Bluetooth Device
2015-05-25 15:02:38.616737 Battery level: 10 % (measurement nr 2))
2015-05-25 15:11:21.447861 Trying to connect (try nr 11)
Successfully Connected to Bluetooth Device
2015-05-25 15:12:49.687791 Battery level: 10 % (measurement nr 2))
2015-05-25 15:16:10.567832 Trying to connect (try nr 3)
Successfully Connected to Bluetooth Device
2015-05-25 15:18:18.354815 Battery level: 4 % (measurement nr 3)))
2015-05-25 15:37:44.169875 Trying to connect (try nr 27)
Successfully Connected to Bluetooth Device
2015-05-25 15:38:44.932914 Battery level: 11 % (measurement nr 2))
2015-05-25 15:42:05.927878 Trying to connect (try nr 3)
Successfully Connected to Bluetooth Device
2015-05-25 15:43:39.133719 Battery level: 10 % (measurement nr 2))
2015-05-25 15:46:19.847809 Trying to connect (try nr 2)
Successfully Connected to Bluetooth Device
2015-05-25 15:47:23.089177 Battery level: 10 % (measurement nr 2)
2015-05-25 15:49:23.659031 Trying to connect (try nr 1)
Successfully Connected to Bluetooth Device
2015-05-25 15:50:32.526885 Battery level: 11 % (measurement nr 2))
2015-05-25 16:40:08.167808 Trying to connect (try nr 72)

The rise time I used was much slower than the requirement mentioned in the data sheet, as seen in the picture below:


In other words, I will continue with the PCB design relying on the reset circuitry of the BL600. At least for the first prototype that should be good enough.

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