Fast Signal Generator minimum output frequency?

Applications, development tools, FPGA, C, WEB
Post Reply
bb11g13
Posts: 8
Joined: Wed Jul 13, 2016 4:54 pm

Fast Signal Generator minimum output frequency?

Post by bb11g13 » Tue Oct 25, 2016 3:57 pm

I want to use one of the fast signal generator outputs on a red pitaya to create a 50Hz sawtooth ramp, which I would like to control from python. According to the SCPI commands list

http://archives.redpitaya.com/devel/SCP ... elease.pdf

the correct way to set the frequency is with

Code: Select all

SOUR<n>:FREQ:FIX ​<value>
where n is the source number and value is a frequency from 0Hz to 62.5MHz. With this in mind, and based on the RF output example on the RP site, I have written the following snippet as part of a python script:

Code: Select all

wave_form = 'SAWU'
freq = 7.65e3
ampl = 1
rp_s.tx_txt('GEN:RST')
rp_s.tx_txt('SOUR1:FUNC ' + str(wave_form).upper())
rp_s.tx_txt('SOUR1:FREQ:FIX ' + str(freq))
rp_s.tx_txt('SOUR1:VOLT ' + str(ampl))
#Enable output
rp_s.tx_txt('OUTPUT1:STATE ON')
With the frequency set to 7.65kHz, or above, everything works as expected, and if I hook up an oscilloscope to the output, as well as if I loop that output back to input 1 I can see the nice smooth sawtooth.

However as soon as I set the source frequency to anything less than the magic number of 7.65kHz (as I should be able to do according to the documentation, which says the RP outputs go down to DC) the signal disappears and I just get a flat line on my scope held at -10mV.

Does anyone know what mistake I'm making, or if this is a known issue, what is the workaround?

Nils Roos
Posts: 1441
Joined: Sat Jun 07, 2014 12:49 pm
Location: Königswinter

Re: Fast Signal Generator minimum output frequency?

Post by Nils Roos » Wed Oct 26, 2016 9:22 pm

I can't reproduce your observation. I just used the same sequence of commands - though from a local netcat session - with a frequency of 100Hz and can see a stable waveform on my scope.
Are you using the scope web application to observe the signal? Using web apps in parallel with the scpi-server can cause problems, so it is not recommended.

videticj
Posts: 4
Joined: Mon Jan 02, 2017 8:52 pm

Re: Fast Signal Generator minimum output frequency?

Post by videticj » Wed Sep 20, 2017 2:28 pm

FYI, I just experienced this same behavior.

After cycling power, it began working normally. My Red Pitaya may have been running for a few days, perhaps even 2-3 weeks, without a power cycle.

Might be some bug hiding that comes out after dark only when you're not looking.

Post Reply
jadalnie klasyczne ekskluzywne meble wypoczynkowe do salonu ekskluzywne meble tapicerowane ekskluzywne meble do sypialni ekskluzywne meble włoskie

Who is online

Users browsing this forum: No registered users and 31 guests