I have to build a cyclic timer that automatically toggles an appliance on and off every 2 hours. I decided to use CMOS logic for this build. The circuit uses an LM555 clock generator to provide the base pulses for a CD4020B 14-stage binary counter. But I can't find similar projects. Can anyone steer me in the right direction?

P.D. I believe a CD4060 would be a better option but I wanna stick with the 4020

 

Hello,

Does this give you an idea?
https://www.electronics-project-design.com/kitchen-timer-circuit.html

Bertus

 

Here's

I believe a CD4060 would be a better option

Yes, it has a built-in oscillator so you don't need the 555.

 

Hello,

Does this give you an idea?
https://www.electronics-project-design.com/kitchen-timer-circuit.html

Bertus

It does, thank u!

 

Here's
Yes, it has a built-in oscillator so you don't need the 555.

Though so! But since it's a uni project, they kinda wanna us to use it.

 

As for the CD4060, I have had problems getting that internal oscillator to function. So I suggest staying withthe CD4020 binary counter. The 555 is a TIMER IC, NOT a clock generator, although it certainly can be used for that purpose.
Switching an appliance will probably require switching mains voltages at some current level. So you should consider how you will isolate the CMOS section from the mains voltage. THAT is important.

 

In addition, going from a CMOS gate output, a few volts at perhaps 2 MILLIAMPS, to a mains level power switch, is a bit involved. It will require at least two stages of transistor gain to drive a CRYDOM SSR to switch mains power. That is the safe and easy scheme, using a good SSR!

 

It will require at least two stages of transistor gain to drive a CRYDOM SSR to switch mains power.

Why two stages?
It only requires 10-20mA to activate them.

 

I am aware of the operating current. But the output current of the counter ICs is quite low. AND, typically a common emitter circuit delivers a logic inversion, thus a second stage to restore the positive output. There may be a work-around scheme possible.
Also, the TS may select some scheme less expensive than a CRYDOM SSR. I mentioned that brand because of the very consistent quality and wide availability. Other brands of SSR dvices will probably be cheaper.

 

typically a common emitter circuit delivers a logic inversion, thus a second stage to restore the positive output.

Since SSRs have isolated floating inputs, you can just high-side drive it by connecting it from V+ to the collector of a single NPN transistor.

 

As for the CD4060, I have had problems getting that internal oscillator to function.

Its internal oscillator is just the standard CMOS multivibrator using two inverting gates.
What type of problems did you have?

 

If you must use a 555-timer IC, use the LMC555 CMOS variety instead of LM555.

 

Or:

https://www.walmart.com/ip/Woods-50...hite/500600518?classType=REGULAR&from=/search

ak

 

Or:

https://www.walmart.com/ip/Woods-50...hite/500600518?classType=REGULAR&from=/search

What's the fun in that?

 

What's the fun in that?

Besides not being any fn at all, based on that very limited description, the setting is in one hour increments. AND, it is a totally mechanical timer scheme. YUK!!!

 

sorry I answered u posting by my solution but since it's a uni project I've been advised not too, but if I can contact any of u via X or discord that'll be awesome! (I get that's no the purpose of this forum )

 

What's the fun in that?

Fr!!

 

sorry I answered u posting by my solution but since it's a uni project I've been advised not too, but if I can contact any of u via X or discord that'll be awesome! (I get that's no the purpose of this forum )

answered you by posting*

 

On this site there is a mechanism called "personal messaging". I have receved a few of those, and been able to respond to them. BUT I have not persued initiating a PM myself. So I guess it is a "Mystery Tool", that works for other people.