Do I need a potentiometer?
July 1, 2013 8:43 AM
We have an alarm for a door that sounds constantly while the door is open. It is run from a 9v transformer that plugs into the wall and the circuit is triggered with magnets on the door. I would like to install volume control for the alarm. Is the correct device a potentiometer? If so, how do I select the correct one? Thanks!
We did try the gaffrer's tape to quiet the alarm and it was effective until we need to turn the volume up again. We need something more permanent that can be manipulated daily.
Not sure what the small magnet idea is though. ... would be interested in hearing more, if only for my education.
posted by lake59 at 9:42 AM on July 1, 2013
Not sure what the small magnet idea is though. ... would be interested in hearing more, if only for my education.
posted by lake59 at 9:42 AM on July 1, 2013
A potentiometer could be part of a solution, but it's not likely to be the whole solution. Not knowing anything about what type of alarm you have or how it was built, I don't think there's nearly enough information here for anyone to suggest an electronic fix.
posted by jon1270 at 9:46 AM on July 1, 2013
posted by jon1270 at 9:46 AM on July 1, 2013
Thanks Jon, great point!
The alarm is a simple Archer 273-075 buzzer (requiring 6-20VDC) powered by a 9VDC transformer. The circuit is completed when the door is opened using a magnetic switch.
posted by lake59 at 10:15 AM on July 1, 2013
The alarm is a simple Archer 273-075 buzzer (requiring 6-20VDC) powered by a 9VDC transformer. The circuit is completed when the door is opened using a magnetic switch.
posted by lake59 at 10:15 AM on July 1, 2013
what lake59 is suggesting is to use a separate handheld magnet to manipulate/deactivate the switch when the door is open. some adhesive velcro would make it perpetually removable.
posted by FauxScot at 10:37 AM on July 1, 2013
posted by FauxScot at 10:37 AM on July 1, 2013
Thanks FauxScot, that is a simple solution! Unfortunately we would like to just turn it down at certain times, not completely off.
posted by lake59 at 11:14 AM on July 1, 2013
posted by lake59 at 11:14 AM on July 1, 2013
Assuming the volume is controlled by the voltage supplied to the buzzer, then yes a pot could work. You can get a 10K pot at Radio Shack for a couple bucks. Without seeing your exact circuit though, no one can tell you exactly how you should look it up. Look up voltage divider on wiki for the general theory.
Bear in mind some things could affect the workability of this, including where in the circuit the switch is, if the switch needs power, if the buzzer needs a minimal current, if there are other things in the circuit, etc...
Also check the transformer. Depending on the type it may have a dial on it to affect the DC output within a slight percentage of the rated output (usually about +/- 10%). This may be enough to get the volume where you want it.
posted by azathoth at 11:17 AM on July 1, 2013
Bear in mind some things could affect the workability of this, including where in the circuit the switch is, if the switch needs power, if the buzzer needs a minimal current, if there are other things in the circuit, etc...
Also check the transformer. Depending on the type it may have a dial on it to affect the DC output within a slight percentage of the rated output (usually about +/- 10%). This may be enough to get the volume where you want it.
posted by azathoth at 11:17 AM on July 1, 2013
Assuming the buzzer is hooked up the simplest possible way (buzzer is directly powered by the transformer and the reed switch on the door just interrupts the power circuit) then a potentiometer will work, though it might not be a very smooth volume control. IME buzzers like that are designed to run off their full voltage and there's probably a pretty narrow range where you've choked off enough of its supply to make it quieter but not so much that it shuts off entirely. It's certainly worth a try though. If it's too finicky to adjust daily you could have a potentiometer *and* a switch that bypasses the potentiometer (a loud/quiet switch).
You could get a quieter buzzer, I suppose. This radioshack page lists the 273-075 as being a 95dB buzzer, but you could replace it with a quieter one like the 273-059 (76dB). Whatever your local radio shack has in stock that'll run off of 9-12v and not more than a couple hundred mA should work. Again, add a switch so you can switch between the loud buzzer and the quiet one.
posted by hattifattener at 7:35 PM on July 1, 2013
You could get a quieter buzzer, I suppose. This radioshack page lists the 273-075 as being a 95dB buzzer, but you could replace it with a quieter one like the 273-059 (76dB). Whatever your local radio shack has in stock that'll run off of 9-12v and not more than a couple hundred mA should work. Again, add a switch so you can switch between the loud buzzer and the quiet one.
posted by hattifattener at 7:35 PM on July 1, 2013
The sound level of most self-driven piezo buzzers is fairly constant with voltage. Most have the element driven by a simple L-C transistor oscillator like this, where power (volume) is more a factor of the element's size and capacitance at resonance. Reducing the voltage simply varies the duty cycle (i.e. tone, not pitch or volume) until you get to the point (as hattifattener says) where the whole thing drops out of resonance and makes a sad strangled gurpling buzz; go much lower than that & it stops oscillating altogether.
So I'm pretty sure a simple pot voltage divider, or changing the supply voltage, won't work well. Simplest solution I can think of is a pair of buzzers - one loud, one soft (maybe a loud one muffled with gaffer tape or blu-tack?) - and a switch to select between them. Or buy a simple & cheap shop door alarm with adjustable volume…
(Also, if it maybe suits your needs, I think that particular RS buzzer can be configured between continuous & beeping? ISTR they're red wire = common +ve, black wire = -ve for continuous, blue wire = -ve for beep?)
posted by Pinback at 9:35 PM on July 1, 2013
So I'm pretty sure a simple pot voltage divider, or changing the supply voltage, won't work well. Simplest solution I can think of is a pair of buzzers - one loud, one soft (maybe a loud one muffled with gaffer tape or blu-tack?) - and a switch to select between them. Or buy a simple & cheap shop door alarm with adjustable volume…
(Also, if it maybe suits your needs, I think that particular RS buzzer can be configured between continuous & beeping? ISTR they're red wire = common +ve, black wire = -ve for continuous, blue wire = -ve for beep?)
posted by Pinback at 9:35 PM on July 1, 2013
This thread is closed to new comments.
posted by a halcyon day at 9:03 AM on July 1, 2013