Laser level detector schematic

What does the star under the resistors R16, R17 and R18 indicate?

  • 8
    \$\begingroup\$ It's probably to indicate there is a note about the resistor somewhere else. \$\endgroup\$
    – DKNguyen
    Jun 26 at 22:39
  • 1
    \$\begingroup\$ The CD4047 is an oscillator IC which frequency is set by a capacitor and a resistor, so probably there's a note somewhere in the schematic. \$\endgroup\$
    – Renan
    Jun 26 at 23:48
  • 3
    \$\begingroup\$ Please post a link to the source of the design. Those resistors set the frequencies of the three oscillators. There probably is a note in the BOM or the design article about how to select them. \$\endgroup\$
    – AnalogKid
    Jun 27 at 0:00
  • 2
    \$\begingroup\$ There are LEDs at the right side used as indicators for MOVE UP, LEVEL OK and MOVE DOWN. But there are sensors at the left side drawn as LEDs but they should be photo diodes. So the quality of this circuit is doubtful. \$\endgroup\$
    – Uwe
    Jun 27 at 0:41

1 Answer 1


The CD4047's are one-shots triggered by optical sensors using LED's (Light emitters are bi-directional as PD's). They each use large caps so a slow pulsing sound is chosen by R to drive the buzzer at unique rates to detect HIGH OK and LOW.

So make LEVEL OK R= 1M or such that the buzzer stays on steady or the duration between pulses,

Then make HI and LO different from each other with smaller R's .

  • \$\begingroup\$ Thank You so much for the reply. This makes sense to me, I'll give it a try. So far, my bread board simulation is nonresponsive to my laser level. I'm wondering if the led's are not the proper ones. Build notes indicate, LED'S with a transparent package and integrated lens (round surface) are used as sensors. Unable to find anything matching the ID listed on the internet. I'm using, 3mm LED DIY White UV Round Water Clear. \$\endgroup\$ Jun 27 at 19:10
  • \$\begingroup\$ FyI; circuit-diagramz.com/… \$\endgroup\$ Jun 27 at 19:21
  • \$\begingroup\$ optics matter. I would use 5mm 30 deg or less is better \$\endgroup\$ Jun 27 at 22:59
  • \$\begingroup\$ Trying to save space. I suspect 5mm would not be that much bigger, I'll give them a try. Thanks for the suggestion. \$\endgroup\$ Jun 29 at 0:08
  • 1
    \$\begingroup\$ > 1m . You can always increase gain on R4,R8,R12 to 10M \$\endgroup\$ Jul 1 at 22:58

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