Power consumption of DS3231 AT24C32 board

parto

Member
Hi, I am trying to use a Picaxe 08M2 Protoboard with a DS3231 AT24C32 RTC module like this one:

https://www.amazon.com/DS3231-AT24C32-Memory-Arduino-Replace/dp/B01L28A70Q/ref=sr_1_16?s=electronics&ie=UTF8&qid=1492633395&sr=1-16&keywords=ds3231

The Picaxe wakes up once a day to check the time on the clock and then goes back to sleep. It does this until a particular date, and then switches a relay.

Everything is working but I measure 0.6 mA at the VCC terminal of the clock module. I had expected the current to be much less than this. I researched the issue and removed the resistors for the LED and the charging circuit (before I did that, the current was over 3 mA).

I have read that some people with Arduinos have disabled functions of the RTC board, etc. to further reduce the power consumption of the RTC, but I didn't understand much of that.

Anyone here have ideas on how to reduce the power consumption of the RTC with this Picaxe setup?

Thank you!
 

pxgator

Senior Member
Hi parto,

You are measuring the VCC running current of the RTC. When it's using the backup coin cell to keep
the time the current usage is only a few micro amps. If you could use the PICAXE to control the VCC power
to the RTC module that would greatly reduce the power demand when the PICAXE is sleeping. Maybe
a low current reed relay or a P-channel FET..??

Cheers to All
 

nick12ab

Senior Member
According to the DS3231 datasheet, the active supply current can be up to 300uA. It's possible the IC on the Chinese board is fake so it could conceivably draw more current than that.

Features such as the square wave output and 32KHz output are enabled or disabled using control registers. Turn of all features that you are not using.

It appears this timekeeper IC is only optimised for low power use when running from the backup battery, in which case it may be a good idea to use a PNP transistor to control the power connection to the board and only turn it on when it is necessary to read the time. You will need to ensure the battery is charged first.
 

hippy

Technical Support
Staff member
Any component with a power consumption of just a few mA or less can usually be safely powered direct from a PICAXE signal line.

One might have to take care with other signals or connections between the two to avoid phantom powering or odd behaviour when turning on or off but it should be achievable.
 

parto

Member
OK, thank you all for your help. I will find out how to control those registers for the square wave output and 32KHz output; these are the ones I read about earlier.

As for controlling the power, the information you've provided about the lower current draw in battery-backup mode greatly clarifies the situation for me.

If I can power the RTC through one of the legs of the 08M2 this simplifies things, but I'm not sure I know how to avoid possible odd behaviors. I need to avoid odd behaviors in this project wherever possible; a lot is riding on the single relay switch at the end.

I'll look at the transistor/relay possibilities too.

I know very little about the need for any extra resistors, etc., that may be needed in either approach, but you've given ways to move forward.
 

parto

Member
Hmm... looks like I've used up my pins on the 08M2; maybe will move up to the 14M2. Will power consumption of the setup on the AXE117 board be about the same as with the 08M2? Thanks.
 

pxgator

Senior Member
The serial out pin (C.0 leg 7) can be used as an output. This could easily power up/down the
RTC module. Is this pin being used other than a serial output..??
 

parto

Member
Pin C.0 and Pin C.4 are being used to activate (with 300 msec pulses) a latching relay (http://www.audiowind.com/pdf/D-151.pdf). This relay has two switch outputs (C1-S1 and C2-S2) that work simultanously. The C1-S1 side is being use to turn on and off a separate 12-V power supply, once a day. The relay activation is timed by the Picaxe's Sleep function.

I need the Picaxe program to read the clock at the same time that I need the relay to turn on the 12-V power supply.

Last night I figured I could just use the C2-S2 side to control the power to the clock board. So that I could use just one 4.5 V power supply for both the Picaxe and the clock, I routed a wire from the VCC side of the relay over to the C2 post, and another wire from S2 to the VCC terminal of the clock board. The SCL and SDA terminals of the clock board remained attached to the Picaxe board. The ground for the clock was routed to the ground for the relay board.

But either the Picaxe board or the relay board didn't like this. Each time the the relay clicked the clock power on (where it was supposed to stay), the relay clicked the switch back back off immediately. When this was repeated several times, the relay stopped working altogether and just made faint clicks.

Supplying separate 4.5V power to C2 works. I'd rather use just one power supply, so if anyone has an idea I'd try it. Thanks!
 
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pxgator

Senior Member
You could try a fairly large (220 to 470 uf) electrolytic bypass capacitor across the single power supply.
This should snuff out any glitchces from the relay turning on/off...??
 

parto

Member
You could try a fairly large (220 to 470 uf) electrolytic bypass capacitor across the single power supply.
This should snuff out any glitchces from the relay turning on/off...??

That sounds like it might solve the problem; I'll try it. Thanks!
 

parto

Member
Strange... I am awaiting my capacitors in the mail, and meanwhile thought I'd advance the rest of my project by using a separate power supply for the clock. The clock board's SCL and SDA contacts are still connected with the Picaxe board, and the VCC and G terminals are connected to a separate 3-AA supply. But I can't get the clock to work with this supply, with or without the relay. Is there some reason that the clock board's VCC and G need to come from the Picaxe's power supply?
 
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