clocks

[dave_1986]

i am currently doing an AS-level electronics project and my project includes a clock, i have made a working 555 astable clock but i need to experiment with other types of clock. So can anyone suggest any other ways of making clocks to me?
+ needs to run at 250Hz +/- 30Hz

 

[Nigel Goodwin]

i am currently doing an AS-level electronics project and my project includes a clock, i have made a working 555 astable clock but i need to experiment with other types of clock. So can anyone suggest any other ways of making clocks to me?
+ needs to run at 250Hz +/- 30Hz

There are many different kinds of oscillators, you could try two transistors as an astable multivibrator, a schmitt trigger gate with feedback around it, opamp oscillators - the list is pretty well endless.

You could even use a micro-controller to do it, an 8 pin PIC would be a lot more accurate than a 555 (I had to get a PIC in here somewhere!).

 

[Kev]

Crystal oscillators

How do you set them up in a circuit and how do i use on to give a short positive pulse every second?

 

[Nigel Goodwin]

Re: Crystal oscillators

How do you set them up in a circuit and how do i use on to give a short positive pulse every second?

Presuming you mean PIC's, there are many different ways to do it. You could use an internal hardware timer to generate interrupts, and count the interrupts. But a simple way would be used nested loops to waste time, so if you wrote a subroutine to delay 1000mS you could do something like this.

Start:

Make output pin high

Make output pin low

Delay one second

Goto Start

That would only take a few lines of PIC code, the biggest part would be the delay routine (and that wouldn't take much). By carefully altering the delay routine you could get a pretty accurate clock pulse - with a 4MHz PIC you can trim the routine to within 1uS.

As it stands, it would produce a very short pulse, to lengthen it simply add another delay routine between the high and low lines - remembering to shorten the main delay by the same amount.