Macronet

Suomenkielinen versio täällä.

Why?

One day I just needed an access control system and reservation calendar to a common use sauna, and it had an electric lock (24VAC) already in place.

Hardware (links to Finnish shops):

• Raspberry Pi 3B
• Enclosure for Raspberry Pi
• Raspberry Pi 7″ TFT
• Enclosure for TFT:lle
• NFC reader
• Relay card module
• Jumper wires
• Good 5V/2A-2.5A PSU, which really gives enough current for RasPi, TFT, NFC-reader and the relay card module
• (or four diodes, capacitor & LM2596 -based DC-DC -variable step-down power supply – in short VAC->VDC transformer + psu, if you steal current from the 24VAC electric lock – not part of this exercise)
• 3G/4G -(usb)dongle & subscription

Stage 1 (memory card):

Raspberry Pi got the newest Raspbian Jessie, which was at the moment in version 2017-06-21. Kernel for the distribution is 4.9.28-v7+.

Stage 2 (assembly):

• detach controller from the TFT (TFT-enclosure required this)
• assemble the TFT enclosure
• attach the controller to the TFT, make sure both cables are in place
• drill holes to the bottom of RasPi enclosure (6mm drill), to use TFT -attachment points
• insert memory card to RasPi
• attach RasPi with it’s enclosure to TFT
• attach the cable from TFT to RasPi, along with 5V(pin4) and Gnd(pin6) with jumper wires
• attach NFC-reader with jumper wires to RasPi, you’ll use pins 1,3,5,11,12,15,16,19,21-26 (f.ex 3.3V, Gnd, i2c & SPI)
  (Explore NFC Board Schematic)
• attach relay card module to RasPi, relay needs ~80mAh of current so take note of this when deciding the PSU
  pins 2 (5V -> VCC), 7 (GPIO -> In1) and 9 (Gnd -> Gnd) are needed
• attach the relay between the another power cable going to the electric lock

Stage 3 (software):

Reader uses SPI, so enable SPI at raspi-config. TFT will rotate by adding display_rotate=1 (90 degrees) or display_rotate=3 (270 degrees) to /boot/config.txt – and console font can be made bigger with dpkg-reconfigure console-setup.

For actual use you need a small stack of software. Relay module must be controller (to open/close door) and NFC-card must be read and validated against some user database. And unless you want to keep the user database up-to-date by hand, there should be something for that also…

My solution was a simple python-service, which reads the NFC-card, validates is against data in MariaDB and after that tells the result on screen & activates the relay if necessary. Almost up to date code can be found at https://macronet.fi/dev/nfc/ (maybe later at github also) – it might work, or not.

Library used for reading the NFC-card is nxppy -that and all other requirements are easy to install:

# sudo apt install python-dev python-pip python-mysqldb cmake mariadb-server-10.0

# pip install nxppy

Stage 4 (installation):

Install the system to the place you want, so that you can show a card to the reader. This might need some cables if you want to take the reader further away – please make note that the reader requires 14 wires (haven’t actually tested if it works without i2c, because it uses SPI) so it’s like 2 cat5e cables.

Stage 5 (why internet connection? and then what?)

Make RasPi to call home/VPN, so that you are able to fix problems remotely.

Or “forget” a wireless keyboard receiver to USB-port and use your new NFC-enabled access control system as an IRC-client.

I had a classic problem, old server without a remote KVM capabilities – if it goes down, no other chances to debug it than going next to it, plug in a monitor and a keyboard.

Then, one day, an epiphany. There is a “Console redirection” in BIOS, and after a quick enable & check – it really worked. BIOS was accessible over serial connection.

Next step, /etc/default/grub (under Debian) open and GRUB_CMDLINE_LINUX="" -> GRUB_CMDLINE_LINUX="console=ttyS0 console=tty0" will enable Linux console through serial. Switching from #GRUB_TERMINAL=console -> GRUB_TERMINAL="console serial" enables Grub to work with serial.

A quick update-grub made the changes active, and during reboot it was confirmed that the whole boot from bios screen to linux login console was accessible through serial connection.

So what about Raspberry Pi?

By default Pi has a serial console active, which can be accessed through GPIO pins 8 & 10 (Pi B+). This needs to be disabled to make console port usable for userspace, by removing console=ttyAMA0 from /boot/cmdline.txt (or by disabling a correct service). After spending less than 1€ on Ebay (to get “MAX3232 RS232 Serial Port To TTL Converter Module DB9 Connector With Cable”) I had the required hardware to connect them together.

– Fits in 1U?  *** Yes

– Pretty setup?  *** No

– Works?  *** Yes

Pi was powered via an USB port on the server backplane, a CAT5e -cable was needed for a network connection and the RS232 -converter was plugged into COM1.

Setup through the COM2 header found in the corner of the motherboard would have been nicer, but it just refused to work.

There’s also cables from the Pi into the reset button -pins on the motherboard, because I needed a way to make a hard reset. Power On/Off could also be managed through power button-pins, but for me it’s quite useless because the Pi is powered by the server through USB (and the server is always on).

Now I can access the Pi through SSH-session and use it to access console on the main server, if I ever need to do so.

GPIO connections (Pi B+ -> other end):
Pin 2 -> RS232 converter: VCC
Pin 6 -> RS232 converter: GND
Pin 8 -> RS232 converter: TXD
Pin 10 -> RS232 converter: RXD
Pin 14 -> Motherboard: Reset GND
Pin 16 -> Motherboard: Reset +

Reset-software (python-rpi.gpio required, don’t blame me if it destroys everything):

#!/bin/python
import RPi.GPIO as GPIO
GPIO.setmode(GPIO.BOARD)
GPIO.setup(16, GPIO.OUT)
# We're currently sinking the current through Pi.
# This causes a "push event" on a reset button.
GPIO.setup(16, GPIO.IN)