Trying to activate car park barrier system with Raspberry Pi - Page 1
Forum section: electronics / beginners

author: huseyinergisi
author_rank: Newbie
timestamp: July 27, 2015, 09:52:38 am
content: HelloI am a student in the UK working on a Nuffield Research project.I am currently working on a Raspberry Pi ANPR (Number Plate recognition system), the current barrier system is manually controlled by pressing a switch on a phone panel. I am looking to connect the Raspberry Pi to the switch and activate it using the GPIO when necessary.Now what I have done is, I have investigated the switch and it seems easy enough to activate. By the looks of it, by pressing the button you are completing a circuit which is opening the barrier.Here is what the circuit board and button looks like:Now from what I believe by connecting the two sides of the switch (the metal screw holes) I will be able to open the barrier? I want to check this with you guys before I go ahead and end up breaking something. If its as simple as connecting the two sides I can connect the Raspberry Pi and complete the circuit on correct detection of a number plate and open the barrier using the GPIO cables.If someone could let me know if that will work or even what these switches are called I can investigate further. If anyone needs I can post more pictures.Thank you.

author: Psi
author_rank: Super Contributor
timestamp: July 27, 2015, 09:58:30 am
content: aww, based on the topic i was hoping for some sort of a hack using a Pi that lets cars get into the car park for free.

author: huseyinergisi
author_rank: Newbie
timestamp: July 27, 2015, 10:01:18 am
content: Oh, that would have been coolMy project is not so helpful

author: McBryce
author_rank: Super Contributor
timestamp: July 27, 2015, 10:45:10 am
content: If you are not sure of the voltage across the switch or whether the switch is high-side or low-side, then the easiest solution would be to use a small relay to short the switch contacts. That way your Pi is completely isolated from the barrier system and you can easily drive a small relay with a few extra parts directly from the GPIO.McBryce.P.s. Do let us know when you've started on the cooler barrier hack

author: Muttley Snickers
author_rank: Unknown
timestamp: July 27, 2015, 11:36:05 am
content: On most intercom systems such as the one you have indicated the switch will most likely be a dry N/O contact and as McBryce has pointed out you might be able to put your relay contact in parallel with it, I cant see any wires for the release going into those terminals so there might be a bit more to it.Yours appears to be a basic system but some systems require the handset to be off hook or even in communication with the gate station before that button is active, other variations will have the control contact in the gate or front door station itself and this is more common, you will need to test this button before you go any further to confirm the units operation, also find out the make and model of the intercom to download any relevant documentation.Most boom and gate controllers have an input that requires a momentay closure on these terminals thats what the intercom button does and if it's over a long distance then it may need a second or two to activate, now this has been discussed before on the forum and there are a number of things to consider and these are important, if your MCU or Pi loses power then you need to make sure that the relay does not trigger or bounce on a restart or for that matter any other unexpected event.Also some boom and gate controller systems will incorporate a ground sensing loop or photo electric beams to ensure that the gates or boom will not close whilst there is an obstruction or vehicle present, some may have a sense loop on the entry side so that the boom or gates cant be activated unless a vehicle is waiting to get in, if these protections are not incorporated in the system then your addition or modification could put people or property at risk, not all systems have these loops or beeams.Additionaly, anything you add or modify needs to be clearly documented and displayed so that other technicians in the future know exactly what you have done or altered and relevant permissions must be sought before commencing any works.All else aside, please keep us updated and good luck.Muttley

author: Aodhan145
author_rank: Frequent Contributor
timestamp: July 27, 2015, 11:42:42 am
content: This may help you it explains how to connect a relay to a raspberry pi.http://itsbrent.net/2013/03/hacking-my-garage-with-a-raspberry-pi/

author: huseyinergisi
author_rank: Newbie
timestamp: July 27, 2015, 12:54:57 pm
content: Thank you very much everyone. Once I have my software working I will use this and create a way to interface with it safely. A relay seems to be the best option here.I will let you know.

author: huseyinergisi
author_rank: Newbie
timestamp: July 27, 2015, 01:00:00 pm
content: Quote from: Muttley Snickers on July 27, 2015, 11:36:05 amYou have made some valid points I haven’t thought about. Thank you I will fix these. We don’t want a barrier coming down on cars randomly/