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Scope triggering , need help
Posted by
cleanworkbench
on 30 Nov, 2017 14:49
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Hello everyone , i,m a newbie here.
Getting back into electronics after many years away from it .
I have just built a single transistor sine wave phase shift oscillator and have the trace on the scope . The scope is a cheap single channel job from the UK circa 1970s a Gould OS 140.
On the front panel there are two 4mm sockets marked Gnd and the other Ext trig / X, next to that is a small insulated pin marked Gate o/p I have no manual on the instrument . However i want to stabilize the sine trace so i need to trigger it with a square wave , right ?.
I,m not sure how to, do i plug the gate o/p into the trig socket or make up a 555 square wave generator say 1khz and put that into the ext/ trig socket , i,m a bit lost here . Can someone clarify please.
Thanks
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#1 Reply
Posted by
macboy
on 30 Nov, 2017 15:03
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Most of the time, the trigger is set to the signal itself. You absolutely can trigger from a sine wave.
If your oscillator is producing a stable signal, and the oscilloscope is not faulty, then you should be able to obtain a nice stable display.
You will not get a stable display by triggering from a completely unrelated (uncorrelated) signal, such as a separate 555 timer. Since the trigger is unrelated to the signal, the scope will start to display the waveform at an essentially random point each time it redraws the screen. At best, the signal will wander or drift left or right, at worst you will just see a garbled mess.
It might help if you can take a clear photo of the front panel of your oscilloscope, set up the way you are trying to view your oscillator signal. People here may be able to find errors in the settings you are using and give you more specific advice.
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#2 Reply
Posted by
fcb
on 30 Nov, 2017 15:13
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Is there a selector on the scope to choose the trigger source, probably with two to four options Free, A, EXT or Line?
If you can't trigger off your input by selecting it on the trigger module, then try daisychaining your signal into the external trig. This assumes that this section is working...
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#3 Reply
Posted by
w2aew
on 30 Nov, 2017 15:45
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Hello everyone , i,m a newbie here.
Getting back into electronics after many years away from it .
I have just built a single transistor sine wave phase shift oscillator and have the trace on the scope . The scope is a cheap single channel job from the UK circa 1970s a Gould OS 140.
On the front panel there are two 4mm sockets marked Gnd and the other Ext trig / X, next to that is a small insulated pin marked Gate o/p I have no manual on the instrument . However i want to stabilize the sine trace so i need to trigger it with a square wave , right ?.
I,m not sure how to, do i plug the gate o/p into the trig socket or make up a 555 square wave generator say 1khz and put that into the ext/ trig socket , i,m a bit lost here . Can someone clarify please.
Thanks
As others have stated, you likely want to set the Trigger Mode to "Internal" to trigger the sweep to the signal itself.
This old video of mine might help, even though the scope is different than what you have, the controls will likely be somewhat similar:
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Thanks for the replies
Well its back to basics here on a budget !!!.
Yes i thought it would have to be triggered by the sine wave and not an independent circuit , so what your saying is possibly a 555 sine to square wave converter tapped onto the phase shift sine wave output and then fed into the external trig socket and the scope lead also onto the phase shift sine wave o/p .
I,ve tried switching to internal but the trace still moves slightly, to control the position of the trace i have to adjust the " variable cal in the the time / div sector , or am i totally confused here .
I will look at the you tube vid.
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#5 Reply
Posted by
w2aew
on 30 Nov, 2017 17:50
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If you could provide a clear picture of the front panel of your scope, we could then advise you how to set it up.
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#6 Reply
Posted by
danadak
on 01 Dec, 2017 12:06
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I will try and get a photo of the scope uploaded .
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#8 Reply
Posted by
danadak
on 03 Dec, 2017 15:37
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The 240 is a 2 channel version of 140 -
Regards, Dana.
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#9 Reply
Posted by
w2aew
on 03 Dec, 2017 15:44
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Try setting the trigger slope to +, the Function to AC, the Trig Sel to Y1 and adjust the Level up and down until you have a steady display of your waveform.
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#10 Reply
Posted by
danadak
on 03 Dec, 2017 16:01
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In addition set your gain so that you see at least 2 major divisions of
waveform pk-pk.
Regards, Dana.
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yep, that,s the scope ive got just its a single channel job. Will try your suggestions for triggering .
Many thanks for replies.
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I've often seen that type of slide switches become intermittent with age, or even fall to bits.
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Yes the switches are a bit dodgy but its all ive got !!!. It needs a teardown and some tlc, it was a freebe years ago.
Well i have had success with the triggering , i flipped the slider switch to internal and rotated the trigger level pot and hey presto a stable trace dont know why i never went to the level pot before , old age i guess LOL.
So i,m a happy bunny now .
Just curios about the OS140 scope , what bandwidth is it rated at , i have no data sheet or manual on it .
Thanks to you all for the input.
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#14 Reply
Posted by
tautech
on 04 Dec, 2017 08:28
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Yes the switches are a bit dodgy but its all ive got !!!. It needs a teardown and some tlc, it was a freebe years ago.
Well i have had success with the triggering , i flipped the slider switch to internal and rotated the trigger level pot and hey presto a stable trace dont know why i never went to the level pot before , old age i guess LOL.
So i,m a happy bunny now .
Just curios about the OS140 scope , what bandwidth is it rated at , i have no data sheet or manual on it .
Thanks to you all for the input.
Internal triggering is indeed required
and the level set within the amplitude of the waveform.
Enjoy your visions into a new world.
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Yeah thanks mate its a new door opening for me .
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#16 Reply
Posted by
mikerj
on 04 Dec, 2017 09:54
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Just curios about the OS140 scope , what bandwidth is it rated at , i have no data sheet or manual on it .
It will almost certainly be in the range 10MHz-20MHz.
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Ok, not fantastic by today's standards but still very useful. Thanks for the info.
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#18 Reply
Posted by
danadak
on 04 Dec, 2017 12:20
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Internet hit shows 10 KMhz. If its a tube scope consider testing tubes
in it, ones in trigger path that grow weak will affect triggering capability.
Also if black beauty caps in scope replace them all -
http://w140.com/tekwiki/wiki/Bumble_Bee_capacitorsRegards, Dana.
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Hmmm , thanks, i will have the case off and inspect.
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#20 Reply
Posted by
danadak
on 04 Dec, 2017 17:28
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Thanks for the links , i will give em a look. Looks very interesting .
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#22 Reply
Posted by
james_s
on 05 Dec, 2017 21:03
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Pretty sure it's solid state, tubes aside from the CRT were pretty much out of scopes by the end of the 60s, aside from a few specialized beasts.
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#23 Reply
Posted by
danadak
on 05 Dec, 2017 23:24
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Tek 70 catalog still dominated by tube scopes. At NSC late into 70s still
545 main scope in factory.
Tube scopes still great, especially plugin series where they addressed specialized
needs. And a tube scope is, unlike solid state/integrated circuit, tough to kill.
Lastly great as a heater....
Regards, Dana.
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#24 Reply
Posted by
james_s
on 06 Dec, 2017 00:54
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I would classify most of those Tek tube scopes as "specialized beasts". They are works of art too, I had a 531A for many years until I passed it on to someone else.
Every small low-medium bandwidth bench scope I've seen from the 70s-on has been solid state.