Rising time

Hey guys,

I am planning to build a multi trigger system on an arduino, which should deliver TTL signals to trigger certain devices (lasers e.g.). However, I have to know how fast the arduino TTL signal rise time is. I haven't really found anything useful yet.

Do you think a rising edge time of 20 ns would be possible with an arduino? If not, maybe with the faster arduino Due?

Thanks!

Maybe you'll get better answers if you tell people why this is important.

Why does this matter to you? I can't see why this is important.

I have to trigger one device
( http://eksmaoptics.com/pockels-cells-and-drivers/pockels-cells-drivers/dpb-high-voltage-pockels-cell-driver/?listtype=search&searchparam=dpb____#attributes)
which requires a rising time of < 20 ns.

The best number I've been able to find is in the SPI section, table in 29.6: SCK: Rise/Fall time: Master 3.6nS Typical

Realizing the Atmega328P is a clocked device, all outputs follow the system clock, then the fastest signals will support a 16 MHz clock, so 31.25nS is the slowest things will be. With 20mA drivers, the outputs will support 20nS no problem unless they are really loaded down with capacitive loads.

The chip is spec'ed to 20MHz, so 25nS rise/fall times would be the absolute slowest one would expect.

If the Arduino pin isn’t fast enough then I suspect you can can find a comparator that is…

mz17: Do you think a rising edge time of 20 ns would be possible with an arduino? If not, maybe with the faster arduino Due?

Thanks!

With a 1GSPS, 100MHz 'scope its impossible to tell how fast the edges are, but at least as fast as 3.5ns (using a low impedance probe, 10% to 90% transition).

Not surprising as its a modern high-speed CMOS process.

My 200 MHz scope has 1.75ns rise time, if I get a chance I'll try and look at some edges tonight. I know 8 MHz signal (SCK at fastest speed) looked fine driving a bunch of shift registers thru a piece of ribbon cable with IDC connectors.