Problem:
I have a 12 position rotary switch and 11 LEDs that I want to switch on one after the other until they are all on (on pos 12).
Limitations:
It would be easy to use a μC, but I wanted to keep this simple and the part count as low as possible
Things I tried:
In my head I planned on using a diode for each pin of the switch to connect it to the previous (works for about 2 leds) but forgot about the diode voltage drop that adds up.
And using a diode for every connection (about 66) is just to much of a mess…
@jonk explains this approach perfectly in his answer below.
Question:
Any elegant ideas what I could do to archive that?
I'm a beginner and probably miss something 🙂
Other ideas
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I found cumulative rotary switches but they seem to be quite rare and I did not find one with 12 positions
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Using an incremental rotary encoder to feed a two shift registers instead (would this work? / might be easier to cave and use a μC)
Best Answer
This answer was written before the OP commented that s/he is using a 3.2 V supply.
simulate this circuit – Schematic created using CircuitLab
Figure 1. The simplest option if a high enough voltage supply is available. With SW8 closed D1 to D7 will light.
simulate this circuit
Figure 2. For lower supply voltages the chain can be split. In this case SW8 being closed lights D7 but also provides a ground to light all the LEDs in the upper chain.
You can further refine Figure 2 for lower supply voltages but would require more and more diodes.
Figure 3. A single-pole 12-way switch will suffice.
Constant current sources (by me):