SparkFun Forums 

Where electronics enthusiasts find answers.

For the discussion of Arduino related topics.
By Ananas>Pineapple
#191513
Hello,

I am using a clock generator (Si5351 from Adafruit) to generate a signal of custom frequency. The output frequency is controlled by an Arduino UNO and it goes to the XTAL1 pin of another Arduino UNO. The problem is that the output frequency has an amplitude of only 3.3V, which is not enough for the other Arduino to work properly. I talked with a guy who did a similar project and he told me to build a "buffer" to increase the signal's amplitude. He gave me some instructions, but I am not experienced enough to understand how I am supposed to connect the components. Here are the instructions:

Use a single inverter to build a buffer. I need to "capacitefy" couple input signal via a capacitor and then take restored signal from the output. He recommended the 74AC series inverter.

So what do I have to do? Which wire I connect where? A schematic would be perfect.
Thanks in advance.
User avatar
By distro inferno
#191610
It seems like a voltage-follower op-amp configuration would work just fine, if you can keep the "skew" low. An op-amp that is too slow would create a delay in the rise and fall time of the clock signal- skew is basically the volts-per-second transition capability of the output of the buffer or voltage follower. An inverter or buffer is just a specialized chip that can do this well. It will amplify the signal from a 3.3V logic square wave to a 5V logic square wave. If the buffer or inverter can handle the frequency range you're sending through it, it should work fine and be easy to wire up. What does the datasheet say for the 74AC chip you're thinking of?
By Valen
#191848
darrellg wrote:Any digital logic IC should have a 0.1uF capacitor between its power pin and ground. The capacitor should be physically located as close to the power pic as possible.
[EDIT]On second read, Ananas>Pineapple probably did mean it like that. I was talking about his friend's suggestion in the OP.

I don't think the suggested capacitor is meant as a power decoupling capacitor, filtering glitches on the supply pin. I think it is meant as a bridge between the (supposedly) AC output of the frequency generator and the DC buffer/driver input. But the Si5351 on the Adafruit board does not have an AC output. The function of the chip is intended to generate other multiple DC clock signals. So the suggestion he got seems unwarranted.

How he should convert the 3.3v squareware into a higher voltage level very much depends on what frequencies he wants to run it. I'm no expert in this, but if it ends up being a dirty sinewave (reduced harmonics or major ringing) then it's going to be a major pain to debug it.