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* 1x LM393 (op amp) analog comparator for voltages
 
* 1x LM393 (op amp) analog comparator for voltages
 
* 1x photoresistor
 
* 1x photoresistor
* 1x pot
 
 
* various resistors & capacitors to produce the right 555 outputs
 
* various resistors & capacitors to produce the right 555 outputs
 
* 1x fabric pressure sensor
 
* 1x fabric pressure sensor
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The photoresistor registers about 140k ohms in inside natural light, held under the bike seat.  In the bathroom with the door mostly shut, simulating nighttime, it registers 22M.  Tentative initial ON value: 20Mohm.
 
The photoresistor registers about 140k ohms in inside natural light, held under the bike seat.  In the bathroom with the door mostly shut, simulating nighttime, it registers 22M.  Tentative initial ON value: 20Mohm.
  
Learned a bit of comparator chip circuit theory from David... Have the op amp circuit breadboarded out such that it turns on one LED when the photoresistor is occluded.  Circuit includes a pot for calibration, forming the second voltage divider.
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Learned a bit of comparator chip circuit theory from David...
 
 
Notes on my pots:
 
 
 
blue pot ranges from 0 ohms to about 2.35k ohms.  the pair of leads swap resistance levels compared to the single lead, such that the total resistance is always about 2.35k ohms.  When the pot is turned all the way to one side, resistance between the single lead and one of the doubles is 0, and from the single lead to the other of the doubles is 2.35.  When it's turned all the way to the other side, the resistances on the double leads, against the single lead, is swapped.
 
 
 
Have the 2 circuit bits combined with a transistor, fully functional.  Drew circuit diagram & breadboarded additional version from diagram to test diagram; made a couple small corrections.  Diagram is correct (possible resistor values s/b changed for optimality as NB supply hadn't anything smaller than 100 ohm).
 
  
 
=== next step ===
 
=== next step ===
Big(?) capacitor behind seat switch s/b sufficient to keep lights on for some time after seat is vacated.  How big must it be?  Test.
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Breadboard out this comparator circuit using a pair of voltage dividers (one with photoresistor, one with dialled variable resistor for calibration).
 
 
Alternately, I have a scribbled diagram that uses a Schmitt trigger which is claimed to be usable for this purpose... research & poke at this more.
 
  
 
I can create the seat cover with embedded pressure switch whenever, it's just a switch, so it can wait until last.
 
I can create the seat cover with embedded pressure switch whenever, it's just a switch, so it can wait until last.

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