Hi again

For some time now I have been in need of an intercom/PA system type circuit where I can have a button and mic in our lounge and run wires to a speaker circuit in our kids bedroom, with the purpose of preventing one of us having to continually run to the room telling the kids to behave or that dinner is ready. We have used a two way office intercom thing bought from ebay https://www.ebay.co.uk/itm/Home-Off...528952&hash=item3b1987dc11:g:aCUAAOSwJ4hY~fFg for a while but it has developed bad interference to the point its unusable.

I done a search on AAC and came across a lot about intercoms but it can be quite confusing finding the correct circuit for my specific needs.
I came across this posted by dodgedave in a separate thread relating to intercom

can I ask would this basic circuit suit my needs, if so how far could the mic and speaker be separated maintaining good working and what kind of output does this circuit have is it clear -ish or have any kind of volume

If one of yous clued up doods could advice me on this or of a better circuit It would help me a lot.

cheers

 

 

View attachment 158949

ha ... well theres one method i suppose...

 

https://www.electro-tech-online.com/threads/intercom-with-two-stations-hard-wired.106440/
Plenty of other designs on www.

 

The circuit in #1 will make about 0.5 to 1 W into 8 ohms. That should be more than enough for a bedroom. A larger speaker (4" -ish) will help with both volume and clarity. Put the electronics near the mic (shortest possible wires) and run the long wires to the speaker. In terms of house dimensions, there is no length limit. The push-to-talk (PTT) switch can be the power switch in series with the battery. The speaker will pop, but who cares - it's a child's intercom. Also, the pop can be seen as a listen-up warning tone; it's a feature, not a bug.

If you don't want to build it from scratch, there are small amplifier modules on ebay for cheap.

ak

 

Hi again

For some time now I have been in need of an intercom/PA system type circuit where I can have a button and mic in our lounge and run wires to a speaker circuit in our kids bedroom, with the purpose of preventing one of us having to continually run to the room telling the kids to behave or that dinner is ready. We have used a two way office intercom thing bought from ebay https://www.ebay.co.uk/itm/Home-Off...528952&hash=item3b1987dc11:g:aCUAAOSwJ4hY~fFg for a while but it has developed bad interference to the point its unusable.

I done a search on AAC and came across a lot about intercoms but it can be quite confusing finding the correct circuit for my specific needs.
I came across this posted by dodgedave in a separate thread relating to intercom

can I ask would this basic circuit suit my needs, if so how far could the mic and speaker be separated maintaining good working and what kind of output does this circuit have is it clear -ish or have any kind of volume

If one of yous clued up doods could advice me on this or of a better circuit It would help me a lot.

cheers

It's possible to repair your existing intercom, but you can buy kits to assemble yourself or ready made ones .

https://quasarelectronics.co.uk/Item/3021-hard-wired-bug-two-station-intercom-kit

 

ha ... well theres one method i suppose...

I was only half joking. I have a built-in intercom in my house but ringing the dinner bell is a far more reliable and certain solution to summon everyone. I guess a big part of that is that in my system, the box in each room has a volume knob. That allows the person in the room to prevent someone from listening in on the always-on mic, but it also turns off any signal coming from the central unit. So I cannot summon everyone to dinner using the intercom and be certain that they heard it, unless they all respond, and that's a pain. If your plan is to have a push-to-talk mic, then the volume can be left to a preset level. Until the kids figure out how to disable it.

 

The circuit in #1 will make about 0.5 to 1 W into 8 ohms. That should be more than enough for a bedroom. A larger speaker (4" -ish) will help with both volume and clarity. Put the electronics near the mic (shortest possible wires) and run the long wires to the speaker. In terms of house dimensions, there is no length limit. The push-to-talk (PTT) switch can be the power switch in series with the battery. The speaker will pop, but who cares - it's a child's intercom. Also, the pop can be seen as a listen-up warning tone; it's a feature, not a bug.

If you don't want to build it from scratch, there are small amplifier modules on ebay for cheap.

ak

Hi thanks for the information Im gonna have a bash at this circuit as I already have most the components in my stockpile,

It's possible to repair your existing intercom, but you can buy kits to assemble yourself or ready made ones

cheers for the link DD these look like a good solution, im gonna try this circuit oot first as i imagine like a lot oh folks on here i enjoy the challenge

I was only half joking. I have a built-in intercom in my house but ringing the dinner bell is a far more reliable and certain solution to summon everyone. I guess a big part of that is that in my system, the box in each room has a volume knob. That allows the person in the room to prevent someone from listening in on the always-on mic, but it also turns off any signal coming from the central unit. So I cannot summon everyone to dinner using the intercom and be certain that they heard it, unless they all respond, and that's a pain. If your plan is to have a push-to-talk mic, then the volume can be left to a preset level. Until the kids figure out how to disable it.

wyane my kids would neglect the bell in a second lol, that sounds like a good system you have, I do have a plan of a similar all room system for in the future and no doubt my kids will figure out how to abuse this intercom but i look forward to the instant silence when they suddenly hear an electronic voice telling them off

 

In the old days, you could buy one of these and assemble it yourself. I did:

 

In the old days, you could buy one of these and assemble it yourself. I did:

Me too
I was trying to find a circuit diagram of it to post, but am unable at the moment.

 

 

You can use a VCO if you want greater efficiency and a less expensive way to power louder speakers. You can use a higher carrier frequency to acheive better audio quality. It is actually pretty similar to in this video. Just maybe add a capacitor to lower the impedance if the inductive reactance gets too high. And obviously replace the HV transformer with a proper speaker!

And one of my attempts to make an arc lighter just turned into a speaker. It was so terrible it was not at all dangerous to touch! I did a frequency sweep and there ended up being a lot of noise.
https://photos.app.goo.gl/w3Z8WRU64cSejToL8

 

Wired or wireless intercom?

https://www.amazon.com/Wireless-Int...coding=UTF8&psc=1&refRID=AD09YAP7ZE91XXPE3WRD

https://www.amazon.com/Intercom-Cen...coding=UTF8&psc=1&refRID=AD09YAP7ZE91XXPE3WRD

 

You can use a VCO if you want greater efficiency

Are you sure you are responding to the right thread? This one is about a simple battery-powered, one-way intercom for a child's bedroom. No oscillators expressed or implied.

ak

 

https://www.electro-tech-online.com/threads/intercom-with-two-stations-hard-wired.106440/
Plenty of other designs on www.

I like this one that was mentioned in the thread at the link above:



What I like about this circuit is the fact that no IC's are needed - just three transistors on each end. And the speakers double as microphones. Simple.

Hmm. As far as I can tell, there should be little to no current drain when the two stations are just idling with both in "receive" mode. Let me look a little harder at the circuit schematic...

Now that I look at it, this circuit is from Colin Mitchell's talkingelectronics.com website down in Australia. I am going to go over to the website and see if Colin has any usage or construction tips for this circuit.

 

Hmm. Now that I look at the schematic, above, where do I get that SPDT momentary switch? You want to press it to connect to the "talk" wire and then have it automatically return to the "receive" side of the circuit when you release it. A N.O. momentary switch won't do that. What do you call this kind of switch? Self-centering?

 

View attachment 159003

Dodgydave, where do you get the "talk/listen" switch? Is it a self-centering switch with "talk" on one side, "listen" on the other side, and "no connection" in the center? That would not work. You don't want to have to hold the switch in the "listen" position to listen. What kind of switch is this creature?

 

Where I used to work (Radio Australia Shepparton) there was an intercom that had a central amplifier. Each station was just a speaker with a transformer to match the 600 Ohm line. A a couple of twin shielded wires ran to the stations, one from the amplifier input and one from the output. A non locking dual changeover toggle switch had each station connected to the amp output. When the switch was operated, the speaker transformer was connected to the amp input and you could speak to all the other stations using the speaker as the microphone. This amp was a 120W RMS valve amp as there were a lot of intercom stations to run. And some were a few hundred meters away. That worked very well for many years.
Now at home, I run a telephone exchange and VOIP phones. A lot better

 

Hmm. Now that I look at the schematic, above, where do I get that SPDT momentary switch? You want to press it to connect to the "talk" wire and then have it automatically return to the "receive" side of the circuit when you release it. A N.O. momentary switch won't do that. What do you call this kind of switch? Self-centering?

SPDT momentary. You can explicitly state "no center off position", but in my experience that is assumed; if you want a center-off position, you have to state it. C&K calls this "On-None-Mom (p/n 7108-whatever). Digi-Key calls it "On-Mom"

https://www.digikey.com/product-detail/en/c-k/U18J2V3QE2/CKN9928-ND/2055206

All of that assumes that you want the push-to-talk switch to be momentary. Back in my TV days the station had a paging intercom (separate from the production intercom with the headsets) connecting the control rooms, Videotape, film,production offices, staging, etc. It had problematic switches. The intended operation was center-off, up was latching (for hands-free talking) and down was momentary talking, but after about a year the switches became intermittent and a continuous headache. I came up with a circuit so that a high-reliability SPST pushbutton switch, like a keyboard switch rated for 10 million operations, performed both functions. Ran for 26 years with zero switch failures.

ak

 

SPDT momentary. You can explicitly state "no center off position", but in my experience that is assumed; if you want a center-off position, you have to state it. C&K calls this "On-None-Mom (p/n 7108-whatever). Digi-Key calls it "On-Mom"

https://www.digikey.com/product-detail/en/c-k/U18J2V3QE2/CKN9928-ND/2055206

All of that assumes that you want the push-to-talk switch to be momentary. Back in my TV days the station had a paging intercom (separate from the production intercom with the headsets) connecting the control rooms, Videotape, film,production offices, staging, etc. It had problematic switches. The intended operation was center-off, up was latching (for hands-free talking) and down was momentary talking, but after about a year the switches became intermittent and a continuous headache. I came up with a circuit so that a high-reliability SPST pushbutton switch, like a keyboard switch rated for 10 million operations, performed both functions. Ran for 26 years with zero switch failures.

ak

You circuit’s switch was SPST?