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Re: Rotary switches for calibration changes, type question
Posted: Wed Nov 30, 2011 9:12 pm
by pat
There was a good reason that I changed from resistor ladders to diodes.... I'll leave it to the reader to figure out why it was a step in the right direction
Re: Rotary switches for calibration changes, type question
Posted: Wed Nov 30, 2011 9:15 pm
by TimH
Go on, Pat, put me out of my misery and explain, as the temperature variation argument is quite compelling, and my brain hurts lol.
Re: Rotary switches for calibration changes, type question
Posted: Thu Dec 01, 2011 12:47 am
by Chris Wilson
You bought a job lot of diodes?
Re: Rotary switches for calibration changes, type question
Posted: Thu Dec 01, 2011 2:39 am
by Benkku
"Based on..." 0.1 mA - we can't assume current flowing through circuit to that low - when using diodes.
Hence current flowing through circuit is greater than that, as diode does not limit forward flowing current to that low level. So - forward voltage slope is definitely greater than (60 mA).
Re: Rotary switches for calibration changes, type question
Posted: Thu Dec 01, 2011 2:42 am
by Benkku
pat wrote:There was a good reason that I changed from resistor ladders to diodes.... I'll leave it to the reader to figure out why it was a step in the right direction
What that 'good reason' might be?
In my opinion - it is more difficult to measure circuit -in fault finding situations, when using diodes without first powering circuit and/or dismantling switch from instrument panel.
Re: Rotary switches for calibration changes, type question
Posted: Thu Dec 01, 2011 2:42 am
by TimH
Indeed...but temperature curve is worse at lower currents, hence me using that :s
Re: Rotary switches for calibration changes, type question
Posted: Thu Dec 01, 2011 2:47 am
by Benkku
and also worse, than when using foil resistors, despite of flowing current.
Hence - one reason why all ADC binary and laddering circuits, are made with resistors.
Re: Rotary switches for calibration changes, type question
Posted: Thu Dec 01, 2011 9:37 am
by Chris Wilson
I am glad I never went into politics, I'd have started a few wars by now....
I never knew what to me was a simple question would cause so much discourse amongst experts
I think I'll get my coat....
Re: Rotary switches for calibration changes, type question
Posted: Thu Dec 01, 2011 12:29 pm
by Benkku
War - nah... It's just opinions with reasoning why.
Think for example that '60 mV' slope. In switch position 7 'worst case' difference is 420 mV at minimum (actually more than that
) when temp change is approximately 20-30 Deg C. ...Then when you have different forward voltage diodes connected in series, bit more temperature change... - you get the point.
Re: Rotary switches for calibration changes, type question
Posted: Tue Dec 06, 2011 2:51 am
by jalai
Topic started...
Chris Wilson wrote:I want to make some 10 position rotary switches for .....
It is not possible to do 10-position switch with diodes (from 5V supply).
I also wish to know "good" reason to use diodes?