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trouble_DS1307.php 5912 Bytes 02-02-2017 19:22:46
Troubleshooting a DS1307Z
I2C RTC, displaying 165.165.2165
The Setup : A DS1307 on a shield, mated with an Arduino/Genuino
✈ The (unhappy) Circuit
The circuit demanded for a Real Time Clock with I2C. A DS1307 seemed a smart choice. It is powered with +5 V.
As the datasheet specifies a battery voltage from 2 - 4 V, the initial design used 4 x LL4148 (because of the low leakeage current), in series,
to get rid of approx 2 V and therfore land in the middle of the specified range. The charge is stored in a "gold cap".
The original circuit
✈ The (unhappy) Behaviour
The circuit worked nicely after switching on. But, after some days the clock seemed unhappy.
✈ Measurements • Discoveries
The reason is the following : The voltage over the storage capacitor will keep on climbing (up to 5 V), as the current drawn from
the gold cap is very low - and for very low currents, the voltage drop across the diodes is also very low. Zero volts at zero current.
The voltage over the gold cap climbs ...
✈ The (happy) Circuit
As the mechanism - which leads to malfunction - was clear, the solution was also clear. With only one diode, but this time connected
to the +3.3 V, the voltage above the gold cap can never go above the +3.3 V - with a 1N5711 (Schottky Diode) it settles at about 3.0 V -
just the value we aimed for ...
The modified circuit
✈ Share your thoughts
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