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Please Help, Timer circuit needed

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weller racing

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Please Help, Frying my brain trying to figure this out without using processor. I need to be able to activate a voice mesage one year after setting the counter circuit. Need minimal componant count. Using ISD 1420 for message.
 

Russlk

New Member
How accurate do you need to be? If you set a 555 timer for 1 second rate, it is only necessary to divide by 31,536,000. The CD4020 divides by 2^14 = 16384, two CD4020 cascaded will divide by 268,435,500; that is more than enough. The binary number for 31,536,000 is: 1111000010011001110000000, MSB on the left, LSB on the right. The LSB is Q0, so the next digit is Q1 which is pin 9 of the first CD4020. Q13 (pin 2) corresponds to the 5th 1 from the right. Unfortunatly, the next 1 in the binary number corresponds to Q16 (Q2 in the second CD4020) but Q2 is not available, so it will be necessary to use a different IC for the second divider. The CD4040 brings out all 12 Qs, so use that. If you AND all the 1s, the result will be a 1 in one year. For better accuracy, you could use a crystal oscillator and divide down to a 1 Hz rate for the clock.
 

Russlk

New Member
I did this design quickly, I think it is right, let me know if you have a problem. You may have to have the crystal custom made, but that is not expensive (last time I did it anyway).

Oops! I need to add an initial reset to the counter. I tried to change the schematic but the system timed out and it is late.
 

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