Electronics question

Dr.Jeff

Dr.Jeff

True Classic
As many already know I am the full time caregiver for my 96 yo mom, so she's living in the same house. I have a "call" system in the home where she can press a button on a pendant and remote speakers sound a 'chime alarm' - telling me she needs something. In other words it is a one way system to signal me. The speakers are wireless receivers that plug into regular wall sockets, and the pendant is a battery powered transmitter. The button on it activates all of the receivers at once, which can be programmed for the "chime" tune and volume. Unfortunately the system has a fairly limited reach (wireless) for the signal, and the speakers are not loud enough (at full volume) when I'm out on the property or have equipment running. So I'd like to "hotwire" a couple of the receivers to allow two things; 1) keep the receiver located within range but extend a pair of wires from it to a further distance, where, 2) the wires connect to a much louder speaker. But I need some help with how to do this.

I opened one of the receiver-speaker assemblies. It is very simple inside. The 110V supply goes directly to a small circuit board, there are 3 controls buttons (volume, menu up and menu down), then a pair of wires to the onboard speaker. I could not find any schematics for it so I don't know if the circuit board changes the voltage from 110V to something less (I suspect it does). Therefore I don't know what sort of speaker I can attach to the speaker output wires if I splice into them.

Here are photos of what's inside the box (I left them large, click on them to see detail). I'm hoping some of you can look at them and understand what it is, in order to help with the project:

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The red and white wires coming from the bottom are the wall plug. The red and black wires barely showing behind go to the onboard speaker. The onboard speaker says "16 ohm, .25 Watt".

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The three push buttons on the right are as described, volume, menu up and down (for chimes).

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You can see one of the little capacitor cans (I think it is) says 10V on it.

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Here's the little on board speaker.
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It will be easy to clip the two speaker output wires and extend them to a seperate speaker. But what spec of speaker will work? Will I need to add a relay and external amp to power a larger speaker?

Really appreciate any help in doing this. It will be a huge benefit to my mom and I.
 
I think the best approach would be to wire in a jack that you can plug an external speaker/amp into. However, there could be a safety issue because it looks like there is no transformer isolating the circuit from the AC lines. You could use an isolation transformer either between the AC power and the unit's power plug or at the speaker outputs. The first option would be easy because they sell ready made isolation transformers that you can just plug into the wall outlet and it will have one or more outlets to plug your load into.

Another thought I had was to make that unit portable by powering it from a battery rather than the AC line. That would work as long as it is not relying on power line communication to other parts of the system. That capacitor that says 10V on it looks like a filter capacitor for the DC power being supplied to the circuit. If that is the case, you could measure the DC voltage across it to confirm the voltage being supplied. Then, find a battery to connect there and take it for a walk and see if it works.
 
Can the lines to the actual speaker in the unit be measured for voltage to determine what the system runs on? I'm thinking if I know the output voltage then I can use a small amp directly from those two (onboard speaker) wires. Sort of like they used to make a "booster" amp for a car stereo system.

It won't help to make the unit portable because one of the main problems is the transmitter won't reach very far. So the receiver unit needs to remain in close enough proximity and extension wires taken from there to a remote (and louder) speaker.
 
Yes, it would be a good idea to measure the voltage across the speaker terminals with an AC voltmeter. If it is in the ~1 to 1.5 volt range it should be able to drive the low level inputs of an amplified speaker. Or maybe hook it to a Bluetooth transmitter and use a wireless speaker. That should be good for about 10 meters. If you go that route, the isolation issue goes away. Actually, as long as the unit has a polarized plug and the wiring at your place is correct, it shouldn't be an issue. Unfortunately, many places end up with the wires flipped so the neutral is sitting at 120V instead of ground potential.
 
I was able to measure the voltage at the speaker, around .7 VAC. So I think it should work as a line level input to any amplifier? I found some small circuit board type amps (mono) online for very little money. They have a gain control so I assume they will accept a line level input, but there is very little info offered about it. The nice thing is the small size may even fit in the plastic housing for the receiver unit (pictures posted previously), it has quite a bit of unused area inside. These little amps run on 12V and I have some left over "wall wart" 12V power supplies from old electronic devices that no longer function. Just need a suitable speaker for outdoor use. Maybe even a small PA type loudspeaker (keep in mind this is only a doorbell type chime signal). If everything works the way I think it will then this is a really simple conversion. Please let me know if I'm wrong about something here.
 
Thanks for all your input on this. Even if the amplifier idea doesn't work, I can still splice the wires to the onboard speaker and extend them. That way the receiver module can be located indoors where it will get a good signal from the transmitter, but allow the existing speaker to be removed and remounted separately outdoors. That at least solves one problem; currently the receivers work fine anywhere inside but they don't work reliably outside, apparently the stucco exterior walls with "chicken wire" act as a Faraday cage. Although it still won't solve the volume issue (being able to hear it over the noise of equipment). However if the amplifier does work, then maybe even the little existing piezo speaker (in addition to being located outside) might be sufficiently loud. Otherwise a larger speaker could be used. Looking forward to playing with this....yet another learning project with electronics, after my previous failure with the fuel injector pulsing module.
 
Not sure. As far as I can tell I followed the schematic to assemble it from the components listed in various instructions. I used a prototype breadboard to alleviate my poor soldering skills. But it did not function. I tried a couple of variations but no success. It is possible one of the components is defective, or I accidently killed one, or I misunderstood the schematic, not sure. After a couple days playing with it I got frustrated and put it aside. Fortunately the components all come in multiples, so one day I'll try making it again with new parts and hopefully a little more skill form that first-ever attempt at doing this sort of thing.
 
Finally received the little amplifiers and speakers. I wired one of each to one of the receivers in place of the onboard speaker and added a external power supply for the amp. It works but unfortunately it really isn't any louder than the original set up. No idea why not; the amp is a 14 watt mono turned up to full volume, and the speaker does not specify the impedance but it's a similar type as the original - only larger, with a "megaphone", and supposedly 125dB. Compared to the tiny original stuff this should be a big improvement. Very disappointing, and another fail in my quest to do electrical projects. :(
 
Not knowing the impedance of the new speakers, nor the capacity for the amplifier, I thought one reason the newly added amp and larger speaker may not be any louder is the new speakers are much higher impedance than the original one. So I wired two of the new speakers in parallel. My understanding is that lowers the total impedance, which should allow a louder volume. This arrangement was slightly louder, but honestly I can't tell if that may just be because now there are two speakers - and therefore more 'sound'. Without a decibel meter it is not possible to quantify any changes, however the difference was not significant. I'm tempted to try wiring three of the speakers in parallel to see what happens. It may blow the amp but what do I have to lose? As stated previously this whole modification isn't any better than the original setup.

Are there other reasons why the added amp and speaker isn't making things any louder? To review, I removed the original speaker from the "receiver" unit and wired that original (speaker) output into the new amp's input (i.e. line level). Then I wired the new 125 dB speaker to the new amp's output. So my understanding is the new amp should be 'boosting' the original unit's output and feeding it to a louder speaker. But there is no noticeable difference.

@dllubin, any suggestions?
 
Dr.Jeff said:
Not knowing the impedance of the new speakers, nor the capacity for the amplifier, I thought one reason the newly added amp and larger speaker may not be any louder is the new speakers are much higher impedance than the original one. So I wired two of the new speakers in parallel. My understanding is that lowers the total impedance, which should allow a louder volume. This arrangement was slightly louder, but honestly I can't tell if that may just be because now there are two speakers - and therefore more 'sound'. Without a decibel meter it is not possible to quantify any changes, however the difference was not significant. I'm tempted to try wiring three of the speakers in parallel to see what happens. It may blow the amp but what do I have to lose? As stated previously this whole modification isn't any better than the original setup.

Are there other reasons why the added amp and speaker isn't making things any louder? To review, I removed the original speaker from the "receiver" unit and wired that original (speaker) output into the new amp's input (i.e. line level). Then I wired the new 125 dB speaker to the new amp's output. So my understanding is the new amp should be 'boosting' the original unit's output and feeding it to a louder speaker. But there is no noticeable difference.

@dllubin, any suggestions?
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If you have a multimeter, I recommend checking the speaker's impedance at DC with the ohmmeter setting (speaker disconnected from amp). Then, I would check the output of the amp with some sort of constant signal at the input (like a sine wave) using the AC voltmeter function. I would measure it first with no load, and then with the speaker as a load. You will then be able to approximately calculate the power delivered using P = V*V/R. Depending how different the impedance is at the test frequency vs. DC, the could be some error, but this should get you in the ballpark which is all you need at the moment. It will be interesting to see the numbers.

As far as your 2 speaker experiment goes, if the output impedance of the amp is much lower than that of the speakers, the output should approach a factor of 2 vs. one speaker. I recall that a factor of two is just detectable to the ear so maybe your experiment was successful. Now to figure out why it is not loud. Do you have any links to the amp and speakers in question? I'd be curious.
 
What was the external power supply for the amp? Paralleling the ‘speakers halves the impedance and doubles the current required from the amp....ok not quite, it’s more complex but it will do. Loudness is a function of amplifier drive capability, voltage and ‘speaker efficiency which varies wildly, two speaker, one speaker, sealed box, distance, ported, speaker size etc etc etc. A 4” open backed speaker isn’t going to sound loud if you feed it 10w or 100w. If the power supply is weak it may be current clipping and unable to drive the speaker or its not outputting a high enough voltage swing.
 
dllubin said:
If you have a multimeter, I recommend checking the speaker's impedance at DC with the ohmmeter setting (speaker disconnected from amp). Then, I would check the output of the amp with some sort of constant signal at the input (like a sine wave) using the AC voltmeter function. I would measure it first with no load, and then with the speaker as a load. You will then be able to approximately calculate the power delivered using P = V*V/R. Depending how different the impedance is at the test frequency vs. DC, the could be some error, but this should get you in the ballpark which is all you need at the moment. It will be interesting to see the numbers.

As far as your 2 speaker experiment goes, if the output impedance of the amp is much lower than that of the speakers, the output should approach a factor of 2 vs. one speaker. I recall that a factor of two is just detectable to the ear so maybe your experiment was successful. Now to figure out why it is not loud. Do you have any links to the amp and speakers in question? I'd be curious.
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I tried measuring the speaker impedance with a meter but got zero - no idea why.

I don't have any source to test with a sine wave or similar. But honestly I'm not concerned, these amps were really inexpensive so if it blows I don't really care. Also keep in mind this system does not run for more than a couple seconds at a time, doesn't play more than a simple "doorbell" type signal, and is only activated a couple times a day. So even if the speaker impedance is too low it isn't likely to fry things right away.

Today I tried paralleling three of the same speakers. And it was noticeably louder (still not what I'd expect, but some improvement). Again, unsure if it is the added "sound" from having more speakers, or actually more output due to reducing the impedance. However it does seem louder than the original configuration. Worst case scenario I will try running it in this configuration and see how it does.
 
NEG said:
What was the external power supply for the amp? Paralleling the ‘speakers halves the impedance and doubles the current required from the amp....ok not quite, it’s more complex but it will do. Loudness is a function of amplifier drive capability, voltage and ‘speaker efficiency which varies wildly, two speaker, one speaker, sealed box, distance, ported, speaker size etc etc etc. A 4” open backed speaker isn’t going to sound loud if you feed it 10w or 100w. If the power supply is weak it may be current clipping and unable to drive the speaker or its not outputting a high enough voltage swing.
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These little amps use a 12V power supply and recommend "more than 1 amp". But none of these cheap components (and I mean really cheap) offer much detail or specifications. The power source I'm using is from a old laptop computer: 12V, 3 amps. So I think it should be enough. I tried another power source just to test things. It was a 1 amp (12V) supply and I could not tell any difference.

The speakers are supposed to be for outdoor use with a 12V system, so water resistant with their own little plastic enclosure. They are a "horn" type design rated at 125dB. The original speaker on the "receiver" unit was a tiny piezo that was stuck onto the plastic housing with no actual enclosure. So I would expect the new ones to produce more volume/noise level. But they really don't seem to.
 
You are not reading resistance because there is a cap in the horn speaker to prevent low frequencies from playing. You will likely have to take one apart to check the actual resistance.
The 125db rating is that the loudest it is supposed to play, or the sensitivity read as 1 w/m (1 watt of power to the speaker, measured spl from 1 meter away) method? I think that is supposed to be the max. That could mean it needs more power than the amp has to get the cone moving well. Doubling the power or number of speakers will net a 3 db increase. This is barely noticeable.
Do you have any links to what the amp and speaker are, so we can see the information on it?
Decreasing the resistance of the amp by paralleling the speakers on the amp output will let it flow more power. That can lead the amp to overheating or damaging components. As short of a time as it will play I don't think overheating is going to be the limiting factor.

If you were to pull all 3 amps from that power supply at 12 volt then the input power to the amp is 36 watts, efficiency is likely 60 to 80%, so output would be 20 to 30 watts. Running on the recommended 1 amp would net 7 to 10 watts output. If the speaker resistance is higher than the amps rated resistance power is even lower.

For louder volume more power is usually the solution. Changing to a more efficient speaker will work the same as more power. If you have a speaker that is 90 db at 1 w/m you would need to double the power 10 times (1024 watts) to make 120 db. A speaker that is 100 db 1 w/m would need doubled 7 times (128 watts).
 
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Thank you, that all makes sense. It's been decades since I've done much with sound systems beyond the basic car stereo. But as I read your comments things started sounding familiar.

I'll look for the specs for the amps. Sadly there was no specifications given for the speakers other than what I've already said. Honestly I did not expect much from these tiny, inexpensive components. But all I was after was the ability to do two things; 1) mount the receiver box indoors so it can get a good radio signal from the transmitters (call buttons), while having the connected speaker itself mounted outdoors or in the garage where I spend considerable time, and 2) increase the overall volume of the 'call' signal from the speaker when activated, so I can hear it over the other noise.
 
Not sure why the speaker would read zero ohms unless it was shorted or your ohm meter does not read low resistances accurately. If it was a capacitor in a crossover (not likely for a woofer) causing the issue, you would be reading infinite ohms, not zero. As far as efficiency goes, a class B amplifier is limited to about 60%. If you happen to have a class D amplifier, they can be 90+% but I would guess it would advertise the fact that it is class D if it really was.

I still think it would be a good idea to get some measurements. If you can't find a single frequency source (should be an app for that), white noise should work OK for what you are doing. A good way to get white noise is to tune an AM radio to an unused frequency.
 
Normal speaker impedance is 4 or 8 Ohm Do not parallel two 4 Ohm speakers as that will result in 2 Ohm impedance and that may destroy the transistors in the power amplifier.
I think you have a miss match output signal from your device that doesn't fit your amplifier input. If your amplifier is of standard input signal type, check it by connecting it to the AUX or Line Out on a stereo.
 
Bjorn Nilson said:
I think you have a miss match output signal from your device that doesn't fit your amplifier input.
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I suspect this is the case. The little "receiver" unit that I connected it to (see my first post) had a small piezo speaker. I just cut the two wires to it and fed them into the small external amp. Before doing that I measured the output to the speaker as about .7 VAC, so figured it would work like a "line" input to the amp. Maybe I'll try removing the amp again and connecting the speaker leads to the new speakers to see if it is any different than with the amp in place.
 
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