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Scope attenuators 1,2,5, why bother?

So, while waiting for parts to arrive, I have been diddling sketches on an A4 piece of paper, on how to design the the minimal cost attenuator, for the PIC scope I am planning.

Now I peaked at one scope I have here, and it has an 11 position switch

10mv, 20 mV, 50 mV, 100 mV, 200mV, 500mV, 11V, 2V, 5V, 10V, 20V

Now that sucks in a way, as counting to 5 is very difficult, as we all think binary these days ;-)

The other thing that is interesting, is that the PIC ADC is 10 bits, and I have a 64 pixel high LCD. So I actually only need 6 bits (2^6 = 64 if it escaped you) for display. That is still better then 2/100 or 2% accuracy, so fine with me.

So 10 bits in, and use only 6, then we can bit-shift, and use the 4 bits shift to make attenuator steps of 2, 4, 8, 16 This reduces hardware (switching) people!

Then I was thinking: Why not use binary on the settings? much easier. So then you get sensitivity of:

10mV, 20mV, 40mV, 80mV, 160mV per division. And maybe then continue, after switching gain ONCE: 320mV, 640mV, 1.28V, 2.56V, 5.12V per division.

Looks like a need for 2 more steps for higher voltage, 10.24V, and 20.48V / div.

For 64 pixels high and 8 divisions vertical that leaves 8 pixels per division. makes a max voltage of 163.84V full screen (at 1x probe).

We can have a cursor on the trace, and a volts display, so who cares even if it switched ranges in octal ;-)

Reply to
Jan Panteltje
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piece

I am planning.

Like with all things that is what engineers have become used to. Change it and you'll hear complaints. After all a foot still has 12 inches, most currencies go 10-20-50-100, there are 12 months in a year and so on. Remember when they wanted to change a full circle from 360 to 400 degrees? Nobody bit.

That 11V setting is a bit unorthodox though :-)

Most serious HW people do not think binary. Some of them think culinary ;-)

div.

If you want to market the device my advice would be: Don't try to fix a system that works.

--
Regards, Joerg

http://www.analogconsultants.com/
Reply to
Joerg

Multiplying in your head is easy with the numbers 1, 2 or 5 but

1.28, 2.56 or 5.12 would tax my patience and make me question why I bought that @$^*@ binary scope. 3.3 units x 200mv is a lot easier than 4.125 x 160mv. Just my one, two or four cents worth. :-) Mike
Reply to
amdx

On a sunny day (Wed, 16 Jan 2008 20:04:23 GMT) it happened Joerg wrote in :

piece

I am planning.

Sorry, typo, it is 2 x 5.5 tough.

Well, once we had a little together in a large hall where we transferred a million dollar electronics project I did. I was there with Mr Big Boss, and we were all casually dressed. Then there was this guy in black suit that came up to me, and asked if I wanted some champagne. I politely refrained, asked Mr Big Boss, who is that, the waiter? No, he replied, that is the architect of this building.

No, I do not want to market it, although anybody will be free to order some. If it really works out OK I can have some PCBs made perhaps. It is just an experiment.

Reply to
Jan Panteltje

On a sunny day (Wed, 16 Jan 2008 14:20:16 -0600) it happened "amdx" wrote in :

Very wise words. Yes, but the idea is also to read voltages from the digital display (as 1.55Vpp for example). In such a case one could even use continuous variable gain to set sensitivity.

Reply to
Jan Panteltje

piece

am planning.

div.

Sometimes the fastest way to get things done is to break the rules, norms, standards, traditions, customs, codes, trends and styles.

Be electropunk! :)

Based on:

formatting link

D from BC British Columbia Canada.

Reply to
D from BC

piece

I am planning.

You could make the attenuator steps user programmable through some setup menu.

BTW, why torture yourself with a PIC, when you can get a cheap LPCxxxx ARM that can be programmed in C ? The ARM also has a fast multiplier that makes scaling easy.

Reply to
Arlet Ottens

On a sunny day (Wed, 16 Jan 2008 12:31:49 -0800) it happened D from BC wrote in : Sometimes the fastest way to get things done is to break the rules,

It is nice to see the word 'cybernetics' again. I got a lot out of reading a book about cybernetics, when I was a kid. Do not remember who wrote it, but it was very clear, and the best intro to electronics trouble shooting perhaps.

Reply to
Jan Panteltje

On a sunny day (Wed, 16 Jan 2008 21:35:47 +0100) it happened Arlet Ottens wrote in :

mm, but the bit shifts will always be 1,2,4,8, etc..

It is just an experiment, I may do it in FPGA again, as that at least gets me into the > 50 MHz sampling, while PIC will be limited to some kHz (think

25kHz).
Reply to
Jan Panteltje

Trace? Real hackers just need the raw hex from the ADC.

Reply to
a7yvm109gf5d1

I assume you will need to multiply values somewhere in the chain by a calibration value anyway, so the input attentuators can be loosely coupled with the readout steps. The gain switching could do 1/2/4/8/16/... while the display would readout 1/2/5/10 sequence. For each display scale setting you would use the best available gain range.

Arie de Muijnck

Reply to
Arie de Muynck

piece

am planning.

div.

My TDS2012 vertical steps 1-2-5, but the timebase steps 1-2.5-5. Bizarre.

John

Reply to
John Larkin

piece

I am planning.

div.

it

They pretty much all do that including mine (not a Tek).

--
Regards, Joerg

http://www.analogconsultants.com/
Reply to
Joerg

piece

I am planning.

div.

it

Oh wait, I correct my previous post. Not all do that. The trusty old Tek

7000 in the lab goes 1-2-5 for the time base. 
--
Regards, Joerg

http://www.analogconsultants.com/
Reply to
Joerg

25kHz).

Analog Devices ADUC70xx are ARM7 based flash microcontrollers. They will let you sample at 1MHz (in fact you can "overclock" the ADC to

2MHz), at 12 bits. It also has built-in 12 bit DACs - so it could be an arbitrary waveform generator too! Or you could "play back" the captured trace. There is a version with a 20MHz DDS and they all have a (very simple) FPGA. 
--

John Devereux
Reply to
John Devereux

On a sunny day (Wed, 16 Jan 2008 12:56:05 -0800 (PST)) it happened snipped-for-privacy@netzero.com wrote in :

it

I have done that debugging some audio stuff :-)

Reply to
Jan Panteltje

It's a nominally log scale. The other commonly seen one is 1, 3, 10,

30 etc. 1, 2, 5 are very approximately 10^(1/3) and 1, 3, 10 are approximately 10^(1/2) 
--
Jim Backus running OS/2 Warp 3 & 4, Debian Linux and Win98SE
bona fide replies to j  backus  jita  
demon  co  uk
Reply to
Jim Backus

Have you ever posted a picture of your lab in one of the perennial "bench photos" threads, Joerg? :-) I'd certainly like to see all those boat anchors I suspect you have in there!

Reply to
Joel Koltner

I haven't but it ain't easy do do this in a photo. The main area consists of the usual RF gear, things you'd see in any lab where serious analog work is going on. The other stuff is used occasionally and thus tucked into cabinets. The old (huge) Rohde&Schwarz SMF generator, the Boonton megacycle meter, various self-builts and so on.

--
Regards, Joerg

http://www.analogconsultants.com/
Reply to
Joerg

A4 piece

scope I am planning.

shift

/ div.

division.

if it

Yep. Why bother with all those faffy ranges when you've massive dynamic coverage on the PIC ADC. Go something like 1:10:100

Reply to
john jardine

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