#+TITLE: Adjustable resistor / indicator
#+AUTHOR: Svjatoslav Agejenko
#+LANGUAGE: en

* (document settings) :noexport:
** use dark style for TWBS-HTML exporter
#+HTML_HEAD: <link href="https://bootswatch.com/3/darkly/bootstrap.min.css" rel="stylesheet">
#+HTML_HEAD: <script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.min.js"></script>
#+HTML_HEAD: <script src="https://cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/3.3.5/js/bootstrap.min.js"></script>
#+HTML_HEAD: <style type="text/css">
#+HTML_HEAD:   footer {background-color: #111 !important;}
#+HTML_HEAD:   pre {background-color: #111; color: #ccc;}
#+HTML_HEAD: </style>

* General
+ DISCLAIMER: I DO ELECTRONICS AND 3D DESIGN SOLELY AS A HOBBY. THERE
  COULD BE ERRORS THAT CAN RESULT IN ALL KINDS OF DAMAGE. USE THESE
  DESIGNS AT YOUR OWN RISK.

+ This design is released under Creative Commons Zero (CC0) license.

+ Author:
  - Svjatoslav Agejenko
    - Homepage: https://svjatoslav.eu
    - Email: [[mailto://svjatoslav@svjatoslav.eu][svjatoslav@svjatoslav.eu]]

+ See also:
  - [[../../index.html][Other physical projects in this repository]]
  - [[https://www.svjatoslav.eu/projects/][Other projects hosted at svjatoslav.eu]]

* Project description
I needed a way to experimentally find resistance that works best in
certain circuits. Usual potentiometers could not handle required power
dissipation and were not precise enough.

Solution is to build adjustable resistor:

[[file:make.png]]

Logically there is series of resistors that increase in resistance in
the power of 2: 0.5, 1, 2, 4, 8, 16, 32, 64, 128, 256, 512. Each
resistor can be enabled or disabled by a switch. This makes entire
range of 0 -- 1023.5 ohms available with the 0.5 ohms precision.

Schematic:
[[file:schematic.png]]

Here is front panel for switches:
[[file:front%20panel.png]]

Download:
+ [[file:front%20panel.FCStd][FreeCAD project]]
+ [[file:front%20panel.stl][STL file]]

Sometimes I would like to use lightbulbs with various parameters as
test load/indicator. Current device has 4 of them included.

Here is front panel for light bulbs:
[[file:indicator%20panel.png]]

Download:
+ [[file:indicator%20panel.FCStd][FreeCAD project]]
+ [[file:indicator%20panel.stl][STL file]]


After assembly using prototype PCB:
[[file:make,%202.png]]


Following body is used as a case and PCB support:
[[file:body.png]]

Download:
+ [[file:body%20and%20back%20cover.FCStd][FreeCAD project (body + back cover)]]
+ [[file:body.stl][STL file for body]]

Result:
[[file:make,%203.png]]

Cover on the back:
[[file:back%20cover.png]]

Download: [[file:back%20cover.stl][STL file]]

Button covers:
[[file:button.png]]

Download:
+ [[file:button.FCStd][FreeCAD project]]
+ [[file:button.stl][STL file]]