# Looking for working "hello world" example for "function probe" with "signal probe"

**URL:** <https://www.ruby-forum.com/t/looking-for-working-hello-world-example-for-function-probe-with-signal-probe/218332>\
**Category:** GNU Radio\
**Created:** [March 28, 2012, 3:05pm UTC](https://www.ruby-forum.com/t/looking-for-working-hello-world-example-for-function-probe-with-signal-probe/218332 "2012-03-28T15:05:56Z")\
**Posts on this page:** 6\
**Page:** 1

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**Author:** ![dubstep](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/cdc98d/32.png) [@dubstep](https://www.ruby-forum.com/u/dubstep)\
**Post date:** [March 28, 2012, 3:05pm UTC](https://www.ruby-forum.com/t/looking-for-working-hello-world-example-for-function-probe-with-signal-probe/218332/1 "2012-03-28T15:05:56Z")

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Hi,

I’m looking for a working “hello world” example for using  
“function probe” with “signal probe” in gnuradio companion.

I can’t get it to work with the existing documentation found.

Thanks for any input.

Mario

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**Author:** ![mario\_behn](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/8e7dd6/32.png) [@mario\_behn](https://www.ruby-forum.com/u/mario_behn)\
**Post date:** [March 28, 2012, 8:21pm UTC](https://www.ruby-forum.com/t/looking-for-working-hello-world-example-for-function-probe-with-signal-probe/218332/2 "2012-03-28T20:21:05Z")

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On Wed, Mar 28, 2012 at 6:04 AM, mario behn [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)  
wrote:

> Hi,
> 
> I’m looking for a working “hello world” example for using  
> “function probe” with “signal probe” in gnuradio companion.
> 
> I can’t get it to work with the existing documentation found.
> 
> Thanks for any input.
> 
> Mario

In the “Function Probe” block you want:  
Block ID: whatever the ID of your “Probe Signal” block is.  
Function Name: level

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<div class="post-metadata">

**Author:** ![mario\_behn](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/8e7dd6/32.png) [@mario\_behn](https://www.ruby-forum.com/u/mario_behn)\
**Post date:** [March 29, 2012, 2:25am UTC](https://www.ruby-forum.com/t/looking-for-working-hello-world-example-for-function-probe-with-signal-probe/218332/3 "2012-03-29T02:25:59Z")

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Actually what should go into the value field of Function Probe?

---

<div class="post-metadata">

**Author:** ![mario\_behn](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/8e7dd6/32.png) [@mario\_behn](https://www.ruby-forum.com/u/mario_behn)\
**Post date:** [April 10, 2012, 3:21am UTC](https://www.ruby-forum.com/t/looking-for-working-hello-world-example-for-function-probe-with-signal-probe/218332/4 "2012-04-10T03:21:51Z")

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Hello:  
I was trying to use the function probe with a custom blocks and it does  
not update its value. I set the block ID correctly and the function  
name. The flow graph executes normally but no change occurs in the  
function probe value. I am using gnuradio 3.5.1. if anyone could help me  
will be great  
thanks in advance  
Damian

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<div class="post-metadata">

**Author:** ![mario\_behn](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/8e7dd6/32.png) [@mario\_behn](https://www.ruby-forum.com/u/mario_behn)\
**Post date:** [March 29, 2012, 2:46am UTC](https://www.ruby-forum.com/t/looking-for-working-hello-world-example-for-function-probe-with-signal-probe/218332/5 "2012-03-29T02:46:58Z")

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On Wed, Mar 28, 2012 at 12:46 PM, mario behn [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)  
wrote:

> Actually what should go into the value field of Function Probe?

Hopefully the attached grc file will clarify things

Value can be anything you want, it is used as the initial value,  
overridden when the function probe is called at poll rate

Jason

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**Author:** ![leadwarrior16](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/48db29/32.png) [@leadwarrior16](https://www.ruby-forum.com/u/leadwarrior16)\
**Post date:** [July 18, 2019, 6:39pm UTC](https://www.ruby-forum.com/t/looking-for-working-hello-world-example-for-function-probe-with-signal-probe/218332/6 "2019-07-18T18:39:17Z")

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Just wanted to post this in the event someone else is looking into this issue:

When GRC creates top\_block.py it will often define the probe call (\_probe\_probe) before instantiating the probe signal block it is referencing, causing python to throw an error.

This can be fixed in top\_block by moving the probe signal block declaration above the probe call definition.

I don’t know of any other blocks with this (bad) behavior, but the GRC team should enforce placing probe call definitions at the end of the blocks section of a flowgraph.