How to time frequency in 555 timer along with a constant output.

Discussion in 'General Electronics Chat' started by Fuji, Nov 8, 2014.

Nov 8, 2014
100
1
Im using an LM555CN timer and want to know how to create any amount of frequency but under any seconds or minutes I choose.

For example:
- 4 hz every 10 seconds
- 1hz every 20 seconds
- 20 hz every 2 minutes

From this, the output should be constant instead of going up or down like it usually does with my 555 timer. If I got 3v going into the timer, I want the output to be 3v constantly without a high or a low from the output.

2. ScottWang Moderator

Aug 23, 2012
5,478
864
You just using a diode to do the commutation process and a capacitor to do the job of waveform filtering.

Nov 8, 2014
100
1
Thanks for the reply. I'll see what I can do with the diodes and get back to you on any issues I have.

As for the constant voltage from the output, I have uploaded a picture of the flashing LED circuit I have to show you where the capacitor is. The LED at the end shows voltage going up and down instead of being a single constant voltage. I already have a capacitor (47uF) for the LED to try to manage a constant voltage but the numbers keep going up and down when the LED is flashing. How can I keep the LED when its turned on to have its voltage not going high or low, but constant continuously as the LED turns on and off?

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Last edited: Nov 8, 2014
4. ScottWang Moderator

Aug 23, 2012
5,478
864
You can't do that when you used a 555 astable oscillator, it will oscillation all the time, unless you want to using a monostable.

5. ScottWang Moderator

Aug 23, 2012
5,478
864
You may need some 555 and a cd4017 to complete your application.

6. ScottWang Moderator

Aug 23, 2012
5,478
864
If you wish to including all the functions then you may need the parts as:
1. 555*4 or CD40106 *1 -- Schmitt NOT Gate Inverter Oscillator.
2. CD4017 *1 -- Decade Counter/Divider with 10 Decoded Outputs.
3. CD4073 *1 -- CMOS AND Gates.
4. CD4520 *1 or CD4040 *1 -- CMOS DUAL UP-COUNTERS.
===================
For example:
- 4 hz every 10 seconds
- 1hz every 20 seconds
- 20 hz every 2 minutes

It just a thought, maybe it need some more parts.

Fuji likes this.

Nov 8, 2014
100
1
Thanks for this info. It will come in handy.

The reason for this is because I have a 3 position potentiometer. These 3 positions have different frequencies (ex. 1hz, 1.5hz, 2hz). Whatever frequency I choose, I need an output of that same frequency but on a time limit like the ones I gave you above (ex. 1hz every 20 seconds, 1.5hz every 50 seconds etc.. etc..). When the time is reached for either of the 3 options, the LED will pulse the frequency.

You gave me 4 options. What do you think is the best component to use for this matter? Most of them have similar concepts as counters except for NOT Gate Inverter.

8. ScottWang Moderator

Aug 23, 2012
5,478
864
That's not 4 options, they all needed in your application, the option only at the individual number.

I will draw a block diagram when I'm free, because I'm quite busy today.

9. ScottWang Moderator

Aug 23, 2012
5,478
864
Could you explain more clearly?

10. ScottWang Moderator

Aug 23, 2012
5,478
864
I'm not sure is this what you want, but you can treat it as a original idea.

Fuji likes this.
11. ScottWang Moderator

Aug 23, 2012
5,478
864
Using two diodes 1N4148 to replace one AND gate.

Fuji likes this.

Nov 8, 2014
100
1
Position 1 is 1hz, Position 2 is 1.5Hz and Poisition 3 is 2Hz on the Potentiometer.
Sorry for not replying sooner, I was busy.

The potentiometer has a knob with 3 positions. Position 1 is 1Hz, Position 2 is 1.5Hz and position 3 is 2Hz.

Thanks for making that circuit diagram. Looks very simple. Yes, that is similar to what I am thinking about. The replacing diodes makes sense as well. I will try this.

One other person told me that if I want a simpler way, it would be a microcontroller and an external crystal oscillator OR an internal oscillator within the microcontroller. I can program the microcontroller to set the time and frequencies when necessary as he said. However, a crystal oscillator would be more accurate in frequency when connected with the microcontroller. Would that be enough for this matter? If this is possible, then I can cut off all the other circuitry and the 555 timer as well.

Last edited: Nov 10, 2014
13. ScottWang Moderator

Aug 23, 2012
5,478
864
Yes, if you want to using a uC that is great, whatever pic, 8051 or even buy a arduino uno board that they all can do the job.

Fuji likes this.