Ds1307 Rtc

[John O]

The datasheet for the AXE033 LCD says that the RTC option provides a programmable alarm output. But the datasheet for the DS1307 itself doesn't seem to have an 'dedicated' alarm output pin.

I was thinking of using the DS1307 in a separate, stand-alone, application that requires accurate 1 hour and 24 hour time intervals (with reference to the actual real time - ie the hour intervals must be "on the hour"). Does the lack of a dedicated alarm output mean the main circuit would have to continually poll the RTC for the time?

If so, can anyone recommend a suitable replacement for the DS1307 which does have an alarm output - preferably in a standard DIL package - which could trigger an interrupt on the main Picaxe.

Thanks,

John.

 

[hippy]

The alarm functionality of the AXE033 is in the main controller chip, not the DS1307. For a standalone DS1307 RTC, to have alarms, you do have to keep polling. That can be aided by using SQW/OUT to generate an interrupt every second, then check the time.

I don't know of a DS1307 equivalent with alarm outputs but Google may help.

 

[russbow]

John, I use the M41T81 chip and love it.
It has the same I2C address as the usual RTC.
Don't know if it's DIL

Russ

 

[hippy]

It may also be worth considering SPI RTC chips. The DS1302 doesn't have alarms nor any SQW/OUT but does have battery trickle charging; the DS1306 adds alarms and SQW/OUT but has a larger footprint. You'll have to compare datasheets for accuracy and full capabilities.

 

[westaust55]

As just mentioned in another thread . . .
The D1S337 which is similar to the DS1307 but no RAM instead has two programmable time-of-day alarms. SOIC package

 

[John O]

Thanks, all, for the ideas.. The DS1306 looks promising.

While looking for the various datasheets, I came across this one - which our local supplier (RS Components) has in stock - albeit it would have to be part of a minimum charge order.

http://docs-europe.electrocomponents.com/webdocs/0424/0900766b804242d4.pdf

Does it look promising?

A normal DIP package is becoming increasingly necessary for me these days, unfortunatey

Edit: The DIP version of the DS1306 is on Maxim's "Samples" list, so it's even more promising

John.

 

[hippy]

The PCF8563 looks promising. It often simply comes down to what you can get your hands on which will do the job.

 

[MartinM57]

PCF8563 doesn't have a battery backup capability but has a usefully low Vdd of 1.8v.

You could try prototyping a poor man's battery backup by feeding:
- your normal +5v source via a diode to the PCF8563 Vdd
- a CR2032 backup battery also via a diode to the PCF8563 Vdd

Can't see why it won't work...then you have a battery backed up RTC with alarms..and one that you can get hold of and in DIP format as well.