i am very new to hardware circuitry and am attempting to connect a wiegand rfid and pin code reader to a raspberry pi for door access control logic. more details at: https://gist.github.com/grenade/d7289df5c83172b82052b2b87df9f978.

in the 2nd photo below, there are 3 wires connected to a bidirectional level shifter (5v - 3.3v). from left to right they are connected as follows:

  • wiegand data 0 - level shifter hv 1
  • wiegand gnd - level shifter hv gnd
  • wiegand data 1 - level shifter hv 4

i intend to connect the level shifter to the raspberry pi as follows:

  • raspi gpio 04 - level shifter hv
  • raspi gpio 06 - level shifter lv gnd
  • raspi gpio 11 - level shifter lv 1 (lower left pin)
  • raspi gpio 12 - level shifter lv 4 (lower right pin)
  • raspi gpio 17 - level shifter lv

i am following a related post which describes a schematic which uses similar hardware.

  • multimeter shows 12v coming from the power supply at the top of the first picture
  • multimeter shows 6v coming from both data 0 and data 1 on the wiegand reader. i was expecting 5.5v, but whatever.
  • multimeter shows 6v coming from both lv 1 and lv 4 on the level shifter. i was expecting a level shift down to 3v ~ 4v.

have i misunderstood what level shifters do or is this one a dud since it outputs the same voltage on the lv end as is going in on the hv end?

power supply and wiegand reader/controller bidirectional level shifter (5v - 3.3v) shifter lv reading level shifter close-up

  • 2
    \$\begingroup\$ Please provide a link to the schematic for your level shifter module. That way we may be able to answer your question. That said also consider that the proper way to connect the power/gnd of the module is to connect them to the proper voltage rails on each side instead of trying to use the rPie GPIOs for that. Also have you made sure to interconnect the GND of powersupply, rPie, receiver and level shifter all together? \$\endgroup\$ – Michael Karas May 22 '20 at 13:15
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    \$\begingroup\$ Could you draw a schematic of how you have the level shifter set up? The only way for us to see what you are doing right now is to translate your words and photos into a schematic. It would be better if you posted the schematic rather than everyone trying to do it themselves. \$\endgroup\$ – JRE May 22 '20 at 13:16
  • \$\begingroup\$ i've added a close-up of the level shifter. it didn't come with a schematic but this is where i bought it: ebay.co.uk/itm/272249807035 \$\endgroup\$ – grenade May 22 '20 at 13:25
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    \$\begingroup\$ @grenade - Hi, I haven't gone through all the details in your question (no time right now), but your photo shows you using the level-shifter with the pin headers not soldered to the level-shifter PCB. You do know that the pin headers should be soldered to the PCB, don't you? Are you able to do that? Thanks. \$\endgroup\$ – SamGibson May 22 '20 at 13:38
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    \$\begingroup\$ @grenade: Imagine me doing a facepalm (at my own mistake) right now. I didn't notice that you had the pins just poked through the board rather than soldered down. Fix that first. If it still doesn't work, then we can discuss schematics. \$\endgroup\$ – JRE May 22 '20 at 14:06

Michael Karas' comment contained the answer i needed. once the level shifter was powered on both the hv and lv sides from the respective 5v and 3v sources, the shifter gives the right 3.3v shifted voltage from the data0 and data1 pins.connected and working

  • \$\begingroup\$ Glad you were able to figure it out from my comment. \$\endgroup\$ – Michael Karas May 22 '20 at 15:48
  • \$\begingroup\$ You can accept your own answer after, I think, 8 hours or so to indicate that it is solved. \$\endgroup\$ – Transistor May 22 '20 at 16:38
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    \$\begingroup\$ It still looks like your headers are not soldered to the level shifter. If they were, your breadboard would short its pins. \$\endgroup\$ – StarCat May 22 '20 at 18:42

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