How can I minimize the ICs in a 24-hour analogue timer circuit to one?

Question

I have been trying to design an analogue timer circuit. The circuit needs to be on a 24-hour cycle with the ability to drive a LED light panel at settings of 10 hours on, 14 off; and 12 on, 12 off. Analogue because I want to manufacture these at scale eventually and don't want to deal with microcontrollers.

Accuracy and minimizing drift over time are very important so using a crystal oscillator is required. I had come up with a design using a 32.768 kHz crystal oscillator, two 4060's (14 stage counters, 2^14), some AND gates to get the period to 2.40 hours and then a decade 4017 chip to select the hours I need to then drive a NPN MOSFET on for the LEDs

But of course, this is a lot of chips.

I decided to take apart a simple grow light timer and much to my surprise they have a 16 MHz oscillator and only one IC which I assume is a ripple counter, to break that down to a 2.4 hour cycle they would need 16,000,000/8640 (seconds in an hour) = 1.3824X10^11 = 2^37 - they would need a counter diver with 37 stages.

I have gone through a bunch of parts and the highest stage ripple counter I can find is a 14 stage, which is way way too low for a 2.4/24 hour cycle especially with a 16 MHz oscillator.

Attached is the photo.

So how is this possible? Is this a custom chip and if so how would I get one like this? Affectively reducing 5 ICs in my design down to one! Any feedback/thoughts would be amazing. I feel like I am missing something.

Answer 1

Your ripple counter chips that you have found do not have the big division ratios that you would like. Why not consider a lower frequency oscillator to drive the input of the chip. Watch crystals could be useful. If great accuracy is not needed then use a RC oscillator which is easy to set up on a basic frequency counter. Another way is to use the AC mains which is 50 or 60 Hz depending where you live. The AC mains can be sampled with a small cheap transformer. The long term accuracy will be very good in most countries.

Answer 2

Just as a hint, I had a similar requirement a few decades ago. There were a couple of simple solutions (although not used at that time with a very precise timing) with standard CMOS ICs.

The parts (still in production today) are

• CD4541
• CD4536

They both have some quite long programmable ripple timers. They can have their own oscillator, or if the division ratio fits you well you can still use the advice from @Autistic, using the local 50/60Hz.