next topic »

[on:]

Hi guys,

I'm using the library posted in the playground for PCF8563 RTC

As I'm using this for a low power application, I notice that whenever I use any function provided by the library that only performs write without requesting any data bytes from the RTC, the current consumption (the ATMega328P itself) would go up pretty high 3-4 mA and it stays there. For example, setAlarm and clearAlarm functions. The only differences I notice with these 2 function compared to the rest like formatDate and formatTime is the write and request for data sequence.

I think, there's something in the Wire and TWI library that is causing this although I'm not very sure.
Any guys came across this problem before?

[Reply #1 on:]

Can you be more explicit:

What is your code exactly (ie post your code in code tags).  Are you putting the processor into sleep mode (3-4mA is not "high"
consumption for a 328!).

My intuition would be that something is leaving one of the I2C bus lines pulled low, which it shouldn't.  What value pull-up
resistors do you have on the bus?  What's the supply voltage?

[Reply #2 on:]

Hi Mark,

Yes, I'm putting the processor into sleep mode. It usually goes down to about 0.1 uA without the RTC.

I'm using a 4K7 pull-up for both data and clock.
It's weird because it only happens (higher consumption) when certain call function of the PCF8563 is being used like for example:

Code:

rtc.setAlarm(minute, 99, 99, 99);
digitalWrite(vperiPin, LOW);   
attachInterrupt(1, alarm, FALLING);

Then the MCU will be pushed to sleep soon after that. The vperiPin is used to power the I2C pull-up. So, I turn them off when not using them.
When I used functions like formatDate or formatTime, the current stays low.

If I were to comment out the setAlarm line, then the current goes low again. The current resulting from the attachInterrupt function is negligible. 

[Reply #3 on:]

Hi Mark,

My intuition would be that something is leaving one of the I2C bus lines pulled low, which it shouldn't.

I just did some measurement on the data and clock lines. As the pull-up are being powered by a digital pin (vperiPin) on the Arduino, the measurement looks weird to me:

• With the setAlarm function enabled, both SDA & SCL are around 25 mV and also 25 mV on the other end of the pull-up resistor (on vperiPin which is already being set as low. This is when the current measured is higher (few mA).
• With the setAlarm function commented, both SDA & SCL are around 0.6 V and also 0.6V on the other end of the pull-up resistor (vperiPin is also set low in this case). This is when the current measured is low (uA range).

[Reply #4 on:]

Ah, that's quite likely the problem - sleep mode is pulling the SDA and SCL lines low, causing the RTC input circuits to operate.

I would leave the pull-ups connected to Vcc and make sure the  SDA and SCL pins are set as INPUTs during sleep.