Binary Decade Resistance / CapacitanceBox

Thread Starter

Wendy

Joined Mar 24, 2008
21,848
Now and then I design a project just for the halibut, and put it out there for discussion. It occurs to me thumb wheel switches are not always the best way to program times or a measurement, Binary counting uses much cheaper switches and to ant one with a little training a better way to DIY. Take resistances for example The schematic shown below show one decade range (Drawing in progress). The only design question is what wattage to mage each resistor as this could also make a decent programmable load for power supplies.

Binary Decade Resistotors.png

The switches are actually reversed, if they are open then the resistance is on.

This is the first decade, and also the one where we should use high wattage resistors. As they get larger in the later decades the resistors can be tweaked by paralleling them and putting small values in series.A common cheap DVM is more than accurate enough to adjust the resistances to more precise values.
 
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Thread Starter

Wendy

Joined Mar 24, 2008
21,848
Of course capacitors are much easier.

Binary Decad Caps.png

Since Caps have fewer values than resistors you will have to be more creative. For example ,Two .1uF caps in parallel will make .02uf, and so on.

This technique can be used to make controls for frequency and other applications.

You will have to make allowances for electrolytics. I used the following scheme to protect them:

Cap Box  Protection.png
 
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Yaakov

Joined Jan 27, 2019
1,536
Now and then I design a project just for the halibut, and put it out there for discussion. It occurs to me thumb wheel switches are not always thew best way to program times or a measurement, Binary counting uses much cheaper switches and to ant one with a little training a better way to DIY. Take resistances for example The schematic shown below show one decade range (Drawing in progress). The only design question is what wattage to mage each resistor as this could also make a decent programmable load for power supplies.
An interesting side effect of your approach is the direct application to a digitally controlled load. It makes using an MCU to set the values trivial.
 
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Thread Starter

Wendy

Joined Mar 24, 2008
21,848
It can also be used to set a power supply voltage/current. Of course it is critical you pay attention to resistor wattage.
 

AnalogKid

Joined Aug 1, 2013
8,103
While it is the most efficient in terms of body count, a drawback of this scheme is that most value changes require changing two or more switches. The worst is changing from 7 to 8. Depending on the order in which you switch the switches, the output value can vary wildly. This could be significant when adjusting a live circuit. One solution for this us Grey coding.

https://en.wikipedia.org/wiki/Gray_code

ak
 

Thread Starter

Wendy

Joined Mar 24, 2008
21,848
Of course a pot is the absolute cheapest and least precision way do do it, Never had a pot flame out on me before, though I suppose there is always a first time.
 

AnalogKid

Joined Aug 1, 2013
8,103
Very common back in the tube days. An old mica coupling cap punches through and 300 Vdc appears across a 1 K pot. POOF.

ak
 

KeithWalker

Joined Jul 10, 2017
413
Now and then I design a project just for the halibut, and put it out there for discussion. It occurs to me thumb wheel switches are not always the best way to program times or a measurement, Binary counting uses much cheaper switches and to ant one with a little training a better way to DIY. Take resistances for example The schematic shown below show one decade range (Drawing in progress). The only design question is what wattage to mage each resistor as this could also make a decent programmable load for power supplies.

View attachment 172698

The switches are actually reversed, if they are open then the resistance is on.

This is the first decade, and also the one where we should use high wattage resistors. As they get larger in the later decades the resistors can be tweaked by paralleling them and putting small values in series.A common cheap DVM is more than accurate enough to adjust the resistances to more precise values.
This arrangement really does simplify attenuation switching. I designed a and built an infra-red remote controlled stereo input selector and attenuator for my sound set-up. It was simple to design and works very reliably with an Arduino micro at it's heart.
 

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