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?
Best Answer
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.