i'm having some issues trying to get a circuit to work that i have found on, yes, the infamous instructables. It consists of a diode matrix that goes to the inputs of a BCD4511 decoder IC. It's literally the only article on the subject I can find and i would like to use this concept in a rotary switch indicator. I'll be brutally honest the instructable is half ass at best and it's missing key information. I have replicated his overall design twice and it cooks the SSD and the 4511 chip gets extremely hot. i'll include a link to it at the bottom. If someone can clear up the holes in the design it would be very much appreciated.


p.s. My comments are at the bottom of the instructable with a schematic that i had copied and completed from the original author.

  • \$\begingroup\$ Questions on stack exchange sites are required to stand on their own; links may only supplement. Questions which are meaningless without following a link are not permitted. \$\endgroup\$ – Chris Stratton Jul 25 '19 at 1:18
  • \$\begingroup\$ I'm cool with the link, but like you said the schematic is crap. At any rate, I want to know... does this gizmo make you go faster ;-) \$\endgroup\$ – hacktastical Jul 25 '19 at 1:40
  • \$\begingroup\$ kudos to the stickler, and the basic question is can someone figure out this bullshit(hence the link). The gizmo is to display what gear his bike is in, and i'm trying to use his design to show what position a rotary switch is in, pretty simple concept... thanks though to @Hacktastical, you're cool, you're instruction to put 1k resistors in between the 4511 and the display has eliminated the SSD burnout issue. I think the author of the instructable is FOS cause it does not work to display 0 through 6 on the SSD. I'll look into the MC14532B, see what that's all about thanks. \$\endgroup\$ – user227319 Jul 25 '19 at 5:32
  • \$\begingroup\$ I was curious about this thing. I see there’s aftermarket displays available - even one for less than $9. There’s also a way to do this with only 2 wires between the sensor switch and the display, for about 30 cents in parts (less the display). But where’s the fun in that? \$\endgroup\$ – hacktastical Jul 25 '19 at 5:49
  • \$\begingroup\$ I got er figured out, buddy neglected to include supply voltage, then told me he connected it to 12 volt dc, while neglecting to tell me that he connected it to 12 volt with a voltage divider to drop the voltage to 2/6volts... needless to say, i lowered the voltage going into the 4511 to 3.2vDC using a voltage regulator and now it works flawlessly... no load resistors between the 4511 and the ssd. \$\endgroup\$ – user227319 Jul 25 '19 at 20:01

I don't see any load resistors from the 4511 to the display - you need these to limit the current to the display elements.

For a 12V supply try a value in the 1K ohm range to limit to about 10mA per segment. If brightness is an issue you could try as low as 500 ohm for 20mA. I wouldn't go much lower than that.

The resistors should be at least 1/4W and preferably 1/2 W size to ensure they won't burn up (they will shed heat instead of in the 4511 and the display.)

More: a handy way to encode the switches in a single chip: https://www.onsemi.com/pub/Collateral/MC14532B-D.PDF This should make your board simpler - no more diodes. Yeah, SOIC, I know - use an SOIC to DIP adapter like this one: https://www.digikey.com/products/en?mpart=PA0006&v=315


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