Rotary switches for calibration changes, type question

[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

[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.

[Chris Wilson]

You bought a job lot of diodes?

[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).

[Benkku]

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.

[TimH]

Indeed...but temperature curve is worse at lower currents, hence me using that :s

[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.

[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....

[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.

[jalai]

Topic started...

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?