probe in a robe Re: [sdiy] I have seen the light (litteraly)

[anthony]

----- Original Message ----- 
From: "Ingo Debus" <debus at cityweb.de>

>> So the probe I made out of a broken soldering iron handle, a DMM probe 
>> with a 1Mohm resister and a 30 pf trimmer cap with some wire and a

> Hm, the typical 10x scope probe has a 9 Megohms resistor in it, not 1 
> Megohm. In series with the usual 1 Megohm input resistance of a scope this 
> will give you 10 Megohms.

Actually it was a 10Mohm. I was thinking of the resistor that I used to 
terminate one of the inputs becauyse I thought it was picking up 
interference.

> DIYed or commercial, such a probe has a much better performance than a 
> wire-only "probe". The trimmer cap compensates for the capacitance of the 
> cable. Is there a test generator (rectangle) in your scope? Use it to 
> calibrate the trimmer such that the scope shows a true rectangle.

The test generator waveform is very nice and square - with just a wire even.

> I once tried to DIY a scope probe. It was so flimsy that I immediately 
> went out and bought a probe ;-)

I used hot glue to make mine. I think that's the key. I have two sayings:

If you can't hot glue it, screw it.

If you can't duc' it...


>
> Ingo
>
>