Ok so following on from my previous post here. I have decided to start with the Wiegand wiring interface. I've drawn a diagram below to illustrate how I plan to wire everything up. Would appreciate if any guru can take a look and comment on any mistakes or improvements please. The CD4050BE chip is used to step down the voltage from 5V (coming out of D1/D0) to 3.3V (to the Pi GPIO pins).

One area which I am a little unsure of are my GND connections. Any guidance (or validation) in that specific area would be great as well.

Apologies for the over simplistic line diagram.

EDIT: For the relay, I am using a relay board similar to this. This isn't drawn to detail in the diagram.

enter image description here

  • Driving relays from GPIO was discussed countless times already, e.g. GPIO pin voltage is too low to energize relay Sep 8, 2021 at 11:22
  • Hi @DmitryGrigoryev, thanks for the response. I am using a relay board which is powered by 5V from the Pi. Similar to here. Apologies this wasn't drawn to detail in my diagram.
    – fabbbles
    Sep 8, 2021 at 14:16

1 Answer 1


CD4050B will step the voltage down to VCC (5V), and you need to step it down to 3.3V GPIO level, so it should be connected to 3.3V pin of the Pi instead of 5V. ICs from Texas Instruments accept VCC between 3 and 18V, so powering with 3.3V is OK.

  • My understanding of the D0/1 connections is that they output 5V, however, the GPIO pins are rated to receive 3.3V hence the need for the CD4050 chip to drop the 5V to 3.3V to protect the GPIOs. Using a multimeter to test, this is indeed the case. I hope my understanding is correct.
    – fabbbles
    Sep 8, 2021 at 16:18
  • Hi Dmitry, I have wired up the connections based on your recommendation and tested the output from D1/0 using the pigpio libray here: abyz.me.uk/rpi/pigpio/examples.html. The program reads the keypresses on the keypad well, but nothing happens when I scan an RF card. I also tried this with 2 different readers with the same results. Was wondering if you have any idea what I could be missing?
    – fabbbles
    Sep 12, 2021 at 7:50
  • 1
    I found the problem. Just to close this out, the issue was basic but wanted to share in case anyone comes across it in future. I was scanning MIFARE (13.56Hmz) cards on readers which were for EM (125Khz) (both readers I had lying around happened to be the same as well!), hence nothing was happening when I scanned the cards. Had to look for some EM cards to test and it works fine now. Thanks for the responses.
    – fabbbles
    Sep 13, 2021 at 11:01

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