#### Re: Risetime calculator (in tekwiki)

Hi Tim,
When I was in high school my friend and I built an analog computer with 2 pots and a meter. It multiplied two numbers together and displayed the result on the meter.
When we showed it to my friend's sister she asked us to multiply 2x3.
The result we got was around 8 on the meter. It could have been 9 or 7. It was hard to tell.
She was not impressed.

We looked around for something better to do with our budding career in electronics.
There wasn't much. The only "instrument" I owned was a VTVM. That limits your options.

Dennis Tillman W7PF

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Albert Otten
Sent: Friday, January 17, 2020 1:15 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Risetime calculator (in tekwiki)

Ideally you would use pots (as variable resistors) for which the resistance increases quadratically from ccw to cw. Then compare the sum of the first 3 resistances with the 4th resistance in a bridge circuit and tune the 4th pot to zero reading. I don't think that the quadratic behavior can be approached good enough with log pots and some trimpots and extra resistors.

Albert

On Fri, Jan 17, 2020 at 08:31 AM, Tim Phillips wrote:

from Tim P (UK)
What is this, please? It seems to be a simple analog computer, maybe
with Log pots.
In case the link doesn't work, the device is in tekwiki Other Instruments.

http://w140.com/tekwiki/wiki/Risetime_Calculator

Appears to give f = sqrt(a^2 + b^2 + c^2)

thanks
Tim P

--
Dennis Tillman W7PF
TekScopes Moderator

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