Triggering using Red Pitaya's generator output

[AlexH]

Hi,

I'm doing an experiment which uses one signal output and two signal inputs on Red Pitaya. Unfortunately, those two signal inputs cannot use as trigger, but the output triangular wave can. Therefore I'm wondering is it possible to connect the output to the extension connector and use it as an external trigger? I don't have much experience with electronics before, so can I actually connect to this extension connector?

Any advice would be greatly appreciated! Thanks!

[Nils Roos]

The trigger input on the extension connector is a 3.3V digital input. The voltage range of the RF outputs (+- 1V) is insufficient to reach the digital input's VIH threshold of 2V.

So, connecting the output to the external trigger directly wont work. I see two solutions to this:

1. Some external circuitry with a high speed analog comparator to generate a suitable trigger signal from the analog output
2. A small modification to the FPGA to derive a trigger signal from the AWG logic - if I understood you correctly, you generate the triangular waveform on RF output, don't you ?

[AlexH]

Hi Nils,

I think the second you said was what I'm looking for. Could you be slightly more specific on how to modify the FPGA code to derive trigger signal from the AWG logic? Like what verilog module needed to be changed? Yes I'm generating triangular wave on RF output.

Thank you so much for your reply.

[Nils Roos]

In red_pitaya_asg.v the signals buf_a_rpnt and buf_b_rpnt carry the current read index (0-16383) for channel A and B respectively. If you want to create a trigger the moment a particular sample of the stored waveform is put onto the output, these are the values to compare against.
The generate.c code synthesizes a triangular waveform starting from the positive peak, so for example to trigger on the positive zero-crossing, you'd use 3/4 * 16384 = 12288 as a compare value.

And of course you'll need to route your fresh signal to the red_pitaya_scope module and incorporate it into the trigger conditions.