Which micro controller (with RTC) to use for something really basic?

LesJones

Joined Jan 8, 2017
4,174
Correction to post #20. I have been looking more closely at the ATtiny13A data and have found that it does not have a crystal oscillator option. I will have to look through the data sheets for a more suitable member of the family. The suggested PIC would work but a programmer to program it would be more expensive than the programmer for the ATtiny family.

Les.
 

Thread Starter

seanspotatobusiness

Joined Sep 17, 2016
210
Correction to post #20. I have been looking more closely at the ATtiny13A data and have found that it does not have a crystal oscillator option. I will have to look through the data sheets for a more suitable member of the family. The suggested PIC would work but a programmer to program it would be more expensive than the programmer for the ATtiny family.

Les.
I think I read that the ATtiny25 has a crystal in it. That said, how much accuracy is sacrificed by not having a crystal?
 

LesJones

Joined Jan 8, 2017
4,174
Without the crystal I think the internal oscillator could vary by about +/- 30 ninutes per day. This is for a temperature range of 0 Deg. C to + 40 Deg.C The ATtiny25 or 85 I think would be suitable.

Les.
 

Kjeldgaard

Joined Apr 7, 2016
476
I have a hardware solution to a "once a day timer".

It is still only a function sketch, but with just three standard 4000 CMOS circuits.

With a 32768 Hz crystal, the total number of pulses to be counted are: 24 * 60 * 60 * 32768 = 2831155200.
It can be dealt mainly with binary dividers, so it will be 675 * 2 ^ 22.

The 2 ^ 22 is divided between IC1 and IC2 and then the 675 decoded in Diode / resistor logic on IC2.

When IC1 gives a pulse per 8 seconds, I have chosen not to reset IC1 from the Sync button and 675 decoder. It then gives that the time base is only dependent on the crystal tolerances.

EnOmDagenTimer_1.jpg
 

Thread Starter

seanspotatobusiness

Joined Sep 17, 2016
210
I have a hardware solution to a "once a day timer".

It is still only a function sketch, but with just three standard 4000 CMOS circuits.

With a 32768 Hz crystal, the total number of pulses to be counted are: 24 * 60 * 60 * 32768 = 2831155200.
It can be dealt mainly with binary dividers, so it will be 675 * 2 ^ 22.

The 2 ^ 22 is divided between IC1 and IC2 and then the 675 decoded in Diode / resistor logic on IC2.

When IC1 gives a pulse per 8 seconds, I have chosen not to reset IC1 from the Sync button and 675 decoder. It then gives that the time base is only dependent on the crystal tolerances.

View attachment 122580
Thanks but I'm not sure I understand the diagram. Which of those logic gates are inside IC3?

Without the crystal I think the internal oscillator could vary by about +/- 30 ninutes per day. This is for a temperature range of 0 Deg. C to + 40 Deg.C The ATtiny25 or 85 I think would be suitable.

Les.
Okay, it definitely needs a crystal then! Thanks.
 

Kjeldgaard

Joined Apr 7, 2016
476
IC3 is only the logic for the LED and reset the counter chain by 24h00m00s.

The decoding of the 24h00m00s time is handled by the diodes on the IC2 Q5, Q6, Q10 and Q12, and resistor from Q14
 

LesJones

Joined Jan 8, 2017
4,174
Hi Kjeldgaaed,
I like that design. I can see no reason why it should not work. I think it will be better for the TS than the microcontroller solution as he will not need to get a programmer and learn how to use it. (I have left out having to learn how to write the code as one of us would probably do that for him.)

Les.
 

LesJones

Joined Jan 8, 2017
4,174
Have you tried Farnell ? They sell the CD4521, CD4020 and CD4093 in one off quantities. BUT for orders under £20.00 (Before VAT) they charge £3.95 postage. I keep a list on the computer of things I need to buy and when the total gets to £20.00 I order them.

Les.
 

TQFP44

Joined Sep 3, 2016
51
How about less than £1 + postage for the ic's you will find all you want there also Xtal , led R , C ....
https://www.esr.co.uk/components/products/frame-ics.htm
I am a firm believer in the saying ,' walk before you run ' so I strongly suggest you go with Kjeldgaard's [ excellent ] circuit, Depending on your experience you could have it built in a couple of days. ( on strip board ) You could have it battery powered via 3 x AA cells will run several months , get your £1 ardu-whatever at the same time see what is more rewarding / difficult ... almost anyone can paste code from the www and burn a micro .
 
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