Hello i was wondering how many minutes or seconds does a 1307 real time clock chip miss each month?
No one can tell you because it is different on every single board. It depends on the exact frequency of the crystal.
Depends on the accuracy and tempco of the quartz crystal used. The commonly
used cheap watch crystals are nothing special. A 50ppm crystal would lose/gain
upto 30 seconds a week.
[also the crystal load capacitance should match the DS1307 oscillator to get that
accuracy]
I tested a cheap DS1307 and found a shift of 30 seconds a day!!!!!
josephchrzempiec:
Hello i was wondering how many minutes or seconds does a 1307 real time clock chip miss each month?
None. It's completely 100% accurate.
The crystal you attach to it? Not so much.
I have a cheapo 1307 and it looses about 7 seconds per day (depending on the weather) In comparison a DS3231 I also have is loosing about 1.5 seconds per month.
Riva:
I have a cheapo 1307 and it looses about 7 seconds per day (depending on the weather) In comparison a DS3231 I also have is loosing about 1.5 seconds per month.
i haven't build one yet or have a module was just thinking if the 1307 is good enough. or something different for a real time clock module.
I bought a DS1307 module off an ebay auction for $0.99 been running since 6/13 in a talking clock/thermometer project hasn't lost a full minute yet. Must be lucky.
Grumpy_Mike:
No one can tell you because it is different on every single board. It depends on the exact frequency of the crystal.
Yes elac, you are lucky. I was not. My crystal is very poor.
fungus:
Riva:
I have a cheapo 1307 and it looses about 7 seconds per day (depending on the weather) In comparison a DS3231 I also have is loosing about 1.5 seconds per month.
I will have to make more spelling mistakes if she is going to spank me for it. XD
thank you. what type of crystal do i need how many mhz?
The RTC 1307 uses a 32.768 Khz watch crystal.
The problem here is that the absolute accuracy is heavily determined by the crystal itself and how well
the crystal matches the parallel load of the 1307 oscillator.
The crystal specs are here
Freq 32.768 Khz.
Max series ESR 45 K.
Required Load capacitance 12.5 pf
The problem is that most suppliers of such crystals wont provide you with a datasheet so its essentially luck;.
You may consider the Maxim DS3231, it has the crystal integrated.
zoomx:
You may consider the Maxim DS3231, it has the crystal integrated.
But that still won't be absolutely accurate. Some designes have a trimmer or variable capacitor actress the crystal so you can adjust it to get it accurate.
The other alternitave is to measure how inaccurate it is and compensate in software.
The crystal is inside the chip, there is no trimmer.
I made measurements with DS1302, DS1307, PCF8563 and DS3231 against a PC clock that use a NTP server. The last one is better. I believe the others can be better with a good crystal so if you build your circuit you can get very good precision but if you buy modules it depends on how lucky you are.
Obviously I can compensate via software but you have to make measurements for every module that use external crystal.
zoomx:
The crystal is inside the chip, there is no trimmer.
They have an internal trimming register which you can set via I2C.
Datasheet says they're accurate to 5 or 6 seconds per month (....or worse if it's cold/hot).
A GPS unit is the way to go if you need real accuracy.
You could use a Temperature Compensated Oscillator (TCXO) instead of a crystal, but they cost more than the 1307!
fungus:
They have an internal trimming register which you can set via I2C.
So it is better since every module with this chip can be trimmered! Thanks fungus!!!
The other modules usually don't have any trimmer.
Yes, other options can be GPS, radio signal (like DCF77), NTP.