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range extender for Oscilloscope

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be80be

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I was thinking about making a range extender for a handheld scope

Using a divider has anyone tried this and care to share there ideas. I'm basically looking for digital readings 0 to 5 volts

Mostly looking for the best chip to use to increase range times a 100
 
A simple resistor divider is all you need, I think most carbon resistors will be okay at 500 volts? If not simply use several in series. The voltage handling ability of resistors is not something I ever understood very well.

What is the frequency your scope works at? A resistor divider will work fine for low frequencies, if you need something more serious there are instructions on how to make X100 probes available on the Internet, they're quiet simple consisting of nothing more tan a well shielded resistor and capacitor.
 
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assuming like most scope inputs, your scope has an input impedance of 1Meg and an input capacitance of 30pf, a resistor in series with the center lead of 100Meg, and a cap parallel to the resistor of 0.3pf should give the required division by 100. voltage dividing scope probes work as a voltage divider with the formula Zp/Zin. since Zin is constant all that needs to be changed is Zp. the capacitance ratio needs to remain the same as the resistor ratio to maintain proper frequency response characteristics. otherwise, square waves begin to look like triangle waves or worse. the compensation cap on a scope probe is usually a variable one so the individual probe can be matched properly with the individual scope input. for a division by 100, i would recommend having the divider at the input connector to minimize errors due to cable capacitance.

appendix A of this app note has all the info you need on scope probes and how they work and why.
 
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Wrong range I'm going to divide like 100 mhz down to 1000khz

I've made some nice 10x probes

But thanks for the probe links
 
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Wait what? Mhz to khz? You didn't specify it was a frequency ranging problem, given your text it seemed to indicate you were trying to take a scope that could only handle 5 volts and do a 100X probe. Semantics though.

You could do it using an opamp buffer and heterodyning it with a local frequency source, but that's going to be a bit delicate as you'll need to filter well to avoid erroneous signals, what kind of bandwidth are you aiming for?
 
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so what you need is a prescaler... prescalers don't usually preserve the waveshape. for that you need either a heterodyning converter, or a sampling downconverter.
 
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Wrong range I'm going to divide like 100 mhz down to 1000khz

...........
If you just want the signal divided down and aren't concerned about waveshape then 100 MHz (not mhz);) can be divided down to 1000kHz for a 5V digital signal using a high speed digital decade counter chip such as the 74F190. For minimum input capacitance you might want to mount the chip at the end of your probe with a short wire from the counter input (add a series 1k ohm resistor to help protect the input). Alternately you could use a 10:1 probe at the counter input but you would need a high speed amp to amplify the 0.5V signal at the probe output to the 5V needed by the chip.

Edit: I just realized that the 74F190 and the similar 74F191 are obsolete and I don't know of a substitute that goes to that high a frequency. Perhaps it is still available from some distributor. For example it is listed here but I don't know if it is actually in stock.
 
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Maxim has a chip that looked good I just want to scale it down only want to handle square wave 0 to 5 volts 50Mhz would work. 75Mhz would be better. The scope works great for what it was made for.

I seen something like what I want to make but can't remember what it was called it let you use a slower scope to check frequency of crystals

I guess this is what I would need Digital Down Conversion

Hey I don't no every thing and can't remember half of that LOL.
 
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Maxim has a chip that looked good I just want to scale it down only want to handle square wave 0 to 5 volts 50Mhz would work. 75Mhz would be better. The scope works great for what it was made for.
What part?
Frequency counters work well with a prescalers. It will divide by 10 or 100 or 1000. You can not see the waveform. This is for measuring the frequency only.
 
It wasn't fast enough and the chips I found are not in production
 
I did find a 74HC4017 decade counter available from Digikey that is good to above 60MHz.
 
we could also tell you the obvious..... get a 100Mhz scope... the benchtop variety, not handheld. a good used 100Mhz scope is not expensive these days. a lot cheaper than a handheld scope.

another reason for getting a scope rather than rigging up a prescaler, is that you really need to see some things other than activity when you measure at a clock crystal. also, these days many clock crystals are running on cpu chips that use 3.3V or 1.8V supply rails, and a prescaler that requires a 5V input may not trigger reliably.
 
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I have a bench scope. I was just playing with this one it's handy but it was made for looking at the mains power. Look at the phase.

And catching problems in the power line.

They now sale it big brother it's way faster but I'm not buying it

I was just looking a ideas to use this one at higher frequency which a DDC chip would do that. Thanks for all the post.
 
There is a design

There is a design published by the French Radioplans Loisirs some years ago using the well known NE602 to bring high frequency signals down to 10,7 MHz using available FI filters.

Obviously the target scope has to be 20 Mhz able. Mine (10 MHz) does not qualify :mad:
 
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