I need to build a display with a frequency counter, but the 2 options I'm considering (the only 2 I know) won't work well for the frequency ranges I need: 1Hz to 300MHz.

The first method I know is using a counter IC (something like this using a CD4047 http://www.tradeofic.com/uploadfile/ic-circuit/2009713213549917.gif). I already built one of this with 2 ranges -Hertz and Kilohertzs-, and it works well in the high range; but with low frequencies -the Hertzs range- the display needs to be off for a full second while it counts; so I get an annoying one second on one second off flicker.

The second method I know is using a microcontroller. The problem is that I need it to display frequencies up to 300 MHz; so, I'm not sure how to achieve this -or even if it's possible- with a 20Mhz PIC. I saw a website with the code for a 20MHz PIC that can count frequencies up to 80Mhz; but it's in assembly (which I'm not familiar with) and it doesn't explain exactly how it achieves this with a microcontroller that's 4 times slower.

I was wondering if anyone knows other alternatives to these 2 methods that could handling ranges from 1 Hz to 300 MHz.

Thanks in advance for your help...

 

use a prescaler, a devide by ten counter rated for at least 200 mhz, that will output the frequency devided by 10 or 20 mhz. this one does not need to be displayed. if you need to count higher freequencies, add another high vrequency counter to devide by 10 again. use the microcontroller to keep track of the decimal point.

 

Counters using TTL will only count to 100MHz max. 74F161 will max out at 120MHz.
To get much higher you will have to use ECL. MC10E016 will count to 700MHz minimum and can push to 900MHz.

At the lower range, your resolution will depend on your sampling interval.
You really need to latch the last output while the counter is acquiring new counts. This will avoid the annoying flicker you are mentioning.

 

Hello,

You might want to use a prescaler like the MB501LP.
This will divide the input by 64/65 or 128/129:
http://www.box73.de/download/bauelemente/MB501.pdf

300 Mhz / 64 will be about 5 Mhz, wich could be counted with the pic.

Bertus

 

So it's either a faster counter with a latch, or the microcontroller with an external prescaler.

Thanks for the help. I'll give both a try.