OK, I've been toying with the idea of making a frequency counter. I bought a Arduino Uno and found some Arduino C code for frequency counting. So here's some questions:

1. It is my thought that the "A"rduino needs a TTL input. How can I get this? A comparator? I would like to measure up to 8MHz.
2. Can I run the "A" from an external crystal (or clock) that is faster than 16MHz?
3. If I do need a comparator, it looks like the lm339 is pretty common, but if the best response time is .3us can I subtract that from...oh whatever. I just had a quart.
Just could use some help/ideas.

 

Find out the switching threshold levels of the Arduino input.
As long as you satisfy the threshold levels and don't go beyond the min and max input, you're ok.
A 74LS04 or 74LS14 will do the trick if you want to condition the input signal. You don't need a comparator.

You can overdrive certain chips but then you're on your own. There is no guarantee it will always work if you operate beyond manufacturer's specs.

 

Thanks for a response MrChips! I think this will do for one of my answers.

 

OK, I finally got some 74HC04 Hex Inverters. I'm looking at a couple schematics.

As you might notice, both of these use Schmitt trigger input inverters. Will my 74HC04's work alright? Should I use two inverters?

I think I remember the Arduino accepting voltage inputs of 1.8 - 5 V as a logical 1 (max 40ma) Also, I would like to guarantee my input never exceeds these specs. Ideas? Zeners? Fuse!!?
I am just getting into this hobby, so don't be shy! I promise I won't be negative. Thanks in advance.

 

Just found this: https://learn.sparkfun.com/tutorials/logic-levels
Good to know.

 

The Arduino Uno uses an ATmega 328, check the datasheet for levels, sink/source current etc.

http://www.atmel.com/images/Atmel-8...PA-168A-168PA-328-328P_datasheet_Complete.pdf

 

diode clamp might be suitable on the input to the logic.

 

Any of the above circuits will work. In the third circuit with the two 74HC14, eliminate the 0.1μF at pin-3.
74HC04 will work. One inverter will work.

 

Thanks for the reply Art. I guess I was waiting for people to hold my hand on this one. I guess I just am going to have to dive in. Thanks again one and all. Ready to go!