Warning Horn Cutout - Page 1
Forum section: electronics / beginners

author: Chuggs
author_rank: Newbie
timestamp: August 05, 2019, 06:01:31 pm
content: Let me start by saying my skill level at electronics is in the diaper wearing level.Background: I am a pilot...and am used to pushing buttons, not designing their circuitry. I also have a motorhome. One particular annoyance is the Warning Systems on in the motorhome. When the hydraulic leveling jacks are extended...you must turn ON the ignition to in in order to retract them. At the same time...a very load piezo buzzer sounds if the Ignition is ON and the jacks are not retracted fully. In an aircraft...some of the warning horns can be cancelled by pushing a button. I wanted very badly to add a circuit like this to my coach.I used an automotive relay, a diode, a momentary switch with an led light ring in the bezel... My goal was to turn on the ignition...when the alarm is energized...the LED in the bezel will illuminate and the buzzer will sound. I push the button to cancel the buzzer...buzzer quits sounding, and the light remains illuminated until the alarm signal goes out. Unfortunately, I incorrectly assumed the signal switching was in the 12vdc+ side. So...when my alarm signal ceases...the light in the switch bezel did not extinguish...and the relay does not unlatch.I redesigned the circuit to try and use the alarm signal 12vdc-. The relay won’t latch. I’m electronically challenged....but I’m guessing the Piezo buzzer induces a waveform in the signal, which when looped to the relay coil...isn’t clean enough to cause it to latch.So, back to square one...Can anyone suggest a circuit that would allow me to construct a working Warning Horn Cutout?The idea is to monitor the alarm circuit...and have an LED illuminate whenever the Alarm is active. Be able to acknowledge the warning and push a momentary button which would latch open the circuit to the Piezo Buzzer making it stop. And finally, when the alarm signal itself has stopped...the relay will unlatch, extinguish the LED light in the switch bezel...and the system will be again ready to sound the Buzzer if another Warning Signal becomes active.The photo of my circuit, well...it works on the iPAD, but when Install it in real life, the relay won’t latch...Thanks for putting up will a complete dummy

author: Rigolon
author_rank: Regular Contributor
timestamp: August 05, 2019, 06:32:12 pm
content: Did you measured the input of the piezo buzzer when the alarm is off?My level at electronics isn't much more than yours, so I may say some things that are wrong. But here is what I know (or think that I know)Piezo Buzzer is driven by a PWM signal. So the input you are using on your relay is not the 12VDC you think you are using. Depending on Duty Cycle you could still turn on the relay. But here is what I think it's happening:When the alarm is off the signal is on HIGH state all the time (12VDC), when alarm goes off the signal is switched between On and Off.In your circuitry once the relay is latched ON it will always be on since the signal you are using probably have voltage all the time.So I would ask of you to first measure your input and outputs when alarm is On and Off... if you have an scope it will be even better to know what is happening.If I'm right about the signal i believe you should be able to craft something. Give it a try, if still needs help we are here for you.

author: floobydust
author_rank: Super Contributor
timestamp: August 05, 2019, 07:20:08 pm
content: I tried a solution as a puzzle to solve for fun and did a circuit.The jacks-not-retracted switch could be on the high side (power) or on the low side (ground). It sounds like yours is switching ground, so a latching relay is still possible to mute the alarm.Take a look and see if this is what your RV has for wiring.edit: I forgot to mention the retract switch must go to other stuff, something has to stop the motor?

author: Chuggs
author_rank: Newbie
timestamp: August 05, 2019, 08:12:40 pm
content: Thanks or that input.I think magnetic element buzzers need a pulsed signal waveform to drive them. Piezo I don’t believe need that.The 12vdc+ using a chassis ground latches. It’s the 12vdc- to the buzzer that is the culprit. I have a cheap limited function scope on order so I can view the circuit...with and without the buzzer in the circuit.

author: Chuggs
author_rank: Newbie
timestamp: August 05, 2019, 08:20:28 pm
content: Look like if you release the momentary button the buzzer would sound again...I had a diode to create a latching effect. Worked with 12vdc signal and chassis ground...but wouldn’t unlatch. The attempt to use the same ground as the buzzer resulted in no relay latching.I suppose a pi filter might clean the signal allowing it to latch, and result in a momentary pause before the relay unlatched while the capacitors discharge...

author: Nusa
author_rank: Super Contributor
timestamp: August 05, 2019, 09:20:41 pm
content: Black simulates the existing circuit as you described it.Add a lamp in parallel, in red. If it's an LED, include an appropriate resistor. Lamp operates whenever alarm is on. Easy.Insert a latching relay with a mute switch, in red. Buzzer operates like normal by default. Push the button to energize. Remains energized until alarm condition goes away.I think that's what you asked for.

author: floobydust
author_rank: Super Contributor
timestamp: August 06, 2019, 12:11:13 am
content: I looked and the levelling jack controllers all have safety interlocks for the parking brake being on, transmission in neutral or park, adequate hydraulic pressure, not low fluid level etc. - or else they sound their alarm.What make is the controller? Perhaps it is trying to say something instead of just being annoying.

author: Chuggs
author_rank: Newbie
timestamp: August 06, 2019, 12:10:25 pm
content: HWH is he mfg.The noise is definitely there for a reason. However, once you hear it...you don’t need to listen to it blast for the next couple of minutes. There is a Green “Travel Mode” light that confirms the jacks are fully retracted.If I can find it...there is another alarm I’d like to do the same thing with. The air tank low pressure warning. It sounds whenever the key is on with low air tank pressure. It would be nice to cancel the noise while waiting for the compressor to fill the tanks.The thing I don’t want to do is to flip a switch and completely disable the alarm. I respect the safety issues it’s designed to highlight...just trying to defeat the noise portion momentarily...and allow it to reset itself so that in can warn us of another occurrence.

author: ledtester
author_rank: Super Contributor
timestamp: August 06, 2019, 04:25:38 pm
content: Sounds like you want a relay timer circuit that works like this:- Normally the relay is not energized.- When you press a momentary push button, the relay is energized for some fixed amount of time (like 1 minute) and the de-energizes automatically.You would connect this relay circuit in series with the buzzer. The buzzer is connected to the normally closed contact of the relay. Thus when the relay is energized the buzzer is disconnected from the circuit. This allows you to mute the buzzer for a minute at a time.You can do this with a 555 - I'll try to whip up a schematic.Alternatively, there are plenty of "relay timer" modules you can get which will energize or de-energize a relay for a certain amount of time, but you'll want one with a trigger signal like this one:https://www.ebay.com/itm/163238492336(title: "1-Way Relay Module DC 6-30V Delay Power-off Trigger Delay Cycle Timer Switch")

author: floobydust
author_rank: Super Contributor
timestamp: August 06, 2019, 07:14:20 pm
content: HWH 725: "NOTE: When the jacks are stored with the ignition in the ON position, the warning buzzer will sound until the jacks have retracted to the STORE position.If desired, the jacks can be stored with the ignition key in the accessory position. This will eliminate the warning buzzer while the jacks are retracting."