Discontinuity Alarm - Page 1
Forum section: electronics / beginners

author: gilbenl
author_rank: Regular Contributor
timestamp: August 19, 2015, 06:10:22 pm
content: So I've recently installed some outdoor speakers on my porch and I would very much like to keep them there beyond a simple physical deterrent. Inside the house, the speakers are connected to the amp via a binding post panel (http://www.monoprice.com/Product?p_id=3326&gclid=CI_I0P3ctccCFYQ-aQodPZMI8Q&kpid=103326). However, I used wire so the banana jacks are open.My idea is to add a 4 channel (4 speaker) continuity circuit to the top of the binding posts, which when a circuit becomes open (ie: some yahoo rips one my speakers off the wall), it triggers my home alarm via a one of the unused sensor channels. Any ideas on how to approach this?

author: SeanB
author_rank: Super Contributor
timestamp: August 19, 2015, 07:02:43 pm
content: Simplest is if you used 3 core mains cable, so you can use the unused ground connector as an alarm contact. Otherwise it depends on the amplifier, you have to place a 10 000uf 63V capacitor on the non common terminal in the amplifier, so that there is no DC path back into the amplifier. Then use a 24VDC relay ( the inductance of the coil means it is not going to do anything to audio) to pass a small DC current through the speaker. Will need a supply that is attached to the other terminal of the relay, and the amplifier common, and you will need a VDR ( any voltage from 33V to 100VDC, which is any device rated for 24VAC to 100VAC) to clamp the spike when the relay deenergises. You want a low power relay, so the coil current, which will flow all the time, is not too high. Will work for amplifiers which deliver low power ( 30W or so into 8R, or 50W into 4R speaker, will work on 24V relay. Up to 100W you will use a 48V supply and relay) and where you do not mind the relay might open the NO contact ( used here as a NC contact when the speaker is connected) at very loud levels.

author: gilbenl
author_rank: Regular Contributor
timestamp: August 19, 2015, 10:10:43 pm
content: I think I followed. Also using this as an opportunity to learn some kicad, so please excuse, but also highlight, gross shortcomings in cad convention. I assume I would replicate the attached block for each speaker. Vout is amp CH1 out. Vin is alarm system sensor input. For some reason, I think it works on 14V for the window/door sensors, but will definitely be checking.

author: Mechatrommer
author_rank: Super Contributor
timestamp: August 20, 2015, 01:32:17 am
content: another way with small mcu like pic10f206. one IO output with reverse protection diode to inp+ binding post, one IO input with level shifter if necessary to inp- binding post. during check, send a short HI pulse output to inp+, if no HI pulse detected on inp- then open circuit, another IO will go HI to trigger alarm... BOM: pic10f206, a diode, a level shifter (probably R divider or/and zener depending on max speaker Vin) and thats it.

author: gilbenl
author_rank: Regular Contributor
timestamp: August 20, 2015, 02:38:10 pm
content: Quote from: Mechatrommer on August 20, 2015, 01:32:17 amThis is more in line with what I had originally conceived. In lieu of a PIC, I can build it up with a spare arduino on the bench. I think ultimately I'll need a concatenation of the relay and micro approach since I'm monitoring 4 speaker channels, but have only two inputs on the alarm. I was able to hunt down the installers manual for the panel and found that there are 2 available wired inputs on the panel-they are programmable to monitor NO or NC circuits. Maybe something as simple as an arduino programmed to put 5v through the speaker circuits and trigger a reed relay open should any of the speaker circuits go low?

author: Muttley Snickers
author_rank: Unknown
timestamp: August 20, 2015, 02:58:40 pm
content: Are these speakers you refer to for audio/ music as you did mention an amplifier, if that is what you are trying to protect then just fit reed switches to them and wire back to the alarm control panel with the relevant end of line resistors, if the speakers are alarm sirens then put them in a siren cover with a tamper switch fitted and again the EOLs. If it's exposed wiring that you want to protect then flexible armour conduit will suffice.Depending on the particular system you can also enable horn speaker or siren monitoring.Muttley

author: SeanB
author_rank: Super Contributor
timestamp: August 20, 2015, 08:03:45 pm
content: Quote from: gilbenl on August 19, 2015, 10:10:43 pmC1 other way round, and connected to the speaker direct. The relay negative is connected to the same terminal, and the VDR is across the coil. Power rail stays the same.