# Clock pulse generator

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#### syntaxerror247

##### Newbie level 2
Clock Pulse Generator

Hi,
I want to make a variable (0.2 Hz - 1kHz) clock/pulse generator AND display the generated frequency value (e.g. 1024 Hz) on a 16x2 LCD display or to 7-segment display. I was going to use a 555 timer with a potentiometer to vary the output frequency of the 555, but a friend told me the output of the 555 is not that accurate due to the resistors and capacitors used with the 555 IC.

What do I need this for?: I'm trying to make a small logic trainer and need a variable clock signal generator to use for experiments with 74HC series ICs such as JK F/F and other ICs. It must be able to display the value of the frequency on the output display in real-time as the knob is turned.

Questions:
1- Should I use the 555 to make this circuit? or is there better ways to achieve my goal or making a variable clock generator? I'm open to better ideas and suggestions.
2- How do I make an accurate clock signal that I can vary using a mechanical device such as a potentiometer or maybe a keypad?
3- How do I count the output frequency?
4- How do I display the frequency value on an LCD or 7-segment display (whichever is easier)?

I know a bit about electronics theory (digital and analog) but haven't built any projects yet. This will be my first project.

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#### goldsmith

Hello my friend
You can use a simple schmitt trigger not gate like 40106 and one potentiometer as a frequency control device and a simple capacitor to obtain your aim.
Best Wishes
Goldsmith

#### jpanhalt

Actually, all relaxation oscillators like the 555, inverting Schmitt, and other inverters (see: Fairchild Application Note 118) will show about the same stability with temperature. In fact, the 555 can be conveniently drawn as a Schmitt inverter. I once played with adding a crystal to improve stability of the 555 just for kicks. Here is the comparison:

I let is run several days with a frequenncy counter (Racal-Dana) and it was quite stable. I should add that is the CMOS version of the 555. The non-CMOS version will also work if a pull-up resistor is added as here:

[url]https://www.edaboard.com/attachments/67697d1327147010-555-crystal-tested.png

John

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#### HTA

A microcontroller with a high clock frequency (quartz based) and integrated LCD controller would be a very compact solution. There a several MSP430 solution which would allow this and on the input side a simple potentiometer or a small magnetic encoder, like the iC-MA ( iC-Haus Homepage - product: iC-MA ). The encoder type would give AB pulses out that makes the adjustment of the desired frequency easier than using a potentiometer.

#### syntaxerror247

##### Newbie level 2
Thank you to those who replied. Does anyone else have any suggestions or answers to the questions in the first post? I appreciate your help.

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