baby monitor project

[SGC622]

I have a pair of baby monitors that I would like to turn into a wireless switch. I want to have a 5v relay on the reciever and some kind of switch on the transmitter. so im assuming i have to build something that will convert the on/off from the switch into something that will transmit over the fm band to the reciever to actuate the relay, but my knowledge of circuitry is limited. I have the capacity to understand diagrams and solder and all that stuff as well as some minor electronics but i would appreciate some help from you guys. thanks

Where im at now is:
i have the reciever and the transmitter apart and i unsoldered the speaker and unsoldered the microphone from the circuit, my problem is that i almost feel i need some sort of tone generator and something on the other side that will read it and understand it as on or off.

 

[Hero999]

This is normally done by transmitting a tone.

A 555 timer can be used as a tone generator and a NE567 as a tone decoder which could be used to trigger a divide by 2 counter which could turn a relay on and off.

If you use a speaker and a microphone you won't have to have an electrical connection to the baby monitor.

https://www.electro-tech-online.com/custompdfs/2010/04/LM567.pdf

 

[SGC622]

I would hook the tone generator up to the microphone on the transmitter and the decoder to the speaker on the reciever?

 

[SGC622]

If you use a speaker and a microphone you won't have to have an electrical connection to the baby monitor.

would you mind explaining this for me? is this pointing to an option for another kind of connection?

 

[Hero999]

I would hook the tone generator up to the microphone on the transmitter and the decoder to the speaker on the reciever?

Kind of.

The idea was to connect the tone generator to a speaker which can be placed near the microphone and have a tone decoder with a microphone attached which can be placed near the receiver's speaker.

I think it's best to avoid a direct electrical connection because there's no chance of you ruining your baby monitor.

 

[SGC622]

will the tone generated be audible to everything else in the room aswell as the recieving monitor or is it beyond our audible range?

 

[Hero999]

Yes, it will be audible, I doubt ultrasonics would work because there probably won't be enough bandwidth.

If that's a problem, I suppose it rules that idea out and you need a direct connection.

 

[SGC622]

in your experience is there a buffer you could use for the direct connection so as not to ruin anything, aswell i am having a hard time figuring out how to hook up the decoder you said to use, i looked at the schematic and im not understanding some of it.

 

[Reloadron]

Years ago a popular way of doing this was using a CEX-4000 push button tone module as used in a touch tone phone. I haven't seen one in years but I would think you could cannibalize an old desktop style touch tone phone to get a good 12 tone generator. That could be 12 channels.

Then do as Hero suggest and use one or more 567 tone decoder chips to decode one to twelve tones.

If you want to hear the audio then as was suggested place the tone generator beside the transmitter microphone input and the decoder beside the receiver speaker using a small mic on the receiver. However, if you want it to be silent then just pipe the audio tones from the tone source into the mic input of the transmitter (remove the mic). On the receiver remove the speaker and couple the audio out directly into the 567 decoder circuit.

If you want a circuit for the 567 for using standard telephone tones let me know.

Ron

 

[Hero999]

You need to remove the electrect mic and wire the tone generator in via an attenuator consisting of a potential divider.

What part of the schematic for the tone decoder don't you understand?

 

[SGC622]

what i dont get about the whole thing to start is:
1. how do i sync up the generator with the decoder so that the decoder knows what to look for.
2. Im a little lost as far as how to hook up the LM567
for example it has 1-8 pins here is how far i am with it correct me if im wrong please.
-1 output filter ?
-2 loop filter ?
-3 Input (Positive lead of the speaker)
-4 V+ (+lead of the 9volts)
-5 Timing Resistor ?
-6 Timing Capacitor ?
-7 Gnd (Negative lead of the speaker,- lead of the 9volts, - lead to relay coil)
-8 Output (+lead to relay coil)

3. The 555 i believe i hook that up like this:
-1 GND (lead of mic,- 9volts)
-2 TR (momentary switch)
-3 Q (lead of mic)
-4 RC
-5 CV
-6 THR
-7 DIS
-8 V+ (+9volts)

I am aware i am missing jumpers,capacitors, and resistors. but how do i sync them up so that they understand eachother? do i use the same resistors and capacitors for the 567 as i did the 555 so that it can pick up its specific tone?
is there anyway someone could draw me up a basic diagram for this for me so i can understand, im more visual i can talk numbers and stuff i have to see the components so i can be like oooh thats how that works lol ya know?
Thanks guys sorry for being a pain.

 

[Reloadron]

what i dont get about the whole thing to start is:
1. how do i sync up the generator with the decoder so that the decoder knows what to look for.
2. Im a little lost as far as how to hook up the LM567
for example it has 1-8 pins here is how far i am with it correct me if im wrong please.
-1 output filter ?
-2 loop filter ?
-3 Input (Positive lead of the speaker)
-4 V+ (+lead of the 9volts)
-5 Timing Resistor ?
-6 Timing Capacitor ?
-7 Gnd (Negative lead of the speaker,- lead of the 9volts, - lead to relay coil)
-8 Output (+lead to relay coil)

3. The 555 i believe i hook that up like this:
-1 GND (lead of mic,- 9volts)
-2 TR (momentary switch)
-3 Q (lead of mic)
-4 RC
-5 CV
-6 THR
-7 DIS
-8 V+ (+9volts)

I am aware i am missing jumpers,capacitors, and resistors. but how do i sync them up so that they understand eachother? do i use the same resistors and capacitors for the 567 as i did the 555 so that it can pick up its specific tone?
is there anyway someone could draw me up a basic diagram for this for me so i can understand, im more visual i can talk numbers and stuff i have to see the components so i can be like oooh thats how that works lol ya know?
Thanks guys sorry for being a pain.

OK, let's try this. Attached is a basic configuration using the 567 as a tone decoder. You should see that it bears a resemblance to the one circuit i the data sheet.

The 567 contains a PLL (Phase Locked Loop). Pin 8 of the chip will go low when the input frequency matches the chips center frequency. That center frequency is set by a few external components. The timing resistor and capacitor (R and C)and is (1.1) / (RC). You want the value of R between 2K and 20K for best results. The chip will work with frequencies between .01 and 500 KHz. However, with very low frequencies the chip will take longer to detect the incoming frequency.

In the attached cartoon the timing resistor tied to pin 5 is a variable 25K Ohm resistor. Using a variable resistor allows tuning the 567 to a range of frequencies. In this case the .47 uF input capacitor would tie to the (+) of your speaker lines and common would be common (tied to speaker common).

The parts used in the 555 circuit have nothing to do with the 567 circuit. The purpose of the 555 is simply to be an oscillator source so just a frequency source. The source doesn't have to be a 555 as it can be anything. I mentioned use of a push button tone module from an old telephone earlier. Just think of the 555 as no more than a source. Therefore there is nothing in common about the 555 or 567. All you want is the 555 to be an astable oscillator circuit.

If for example you built an oscillator using the 555 that ran at 1 KHz then you would choose your R & C in the 567 circuit to respond to 1 KHz. If you use a variable timing resistor with the 567 (as I did) you would then output the 555 to the 567 and tune the 567 (using the variable resistor) till pin 8 of the 567 dipped low.

Does that help?

Ron

 

[Reloadron]

OK, here you go. I had some good 567 circuits in an old book I have I likely bought around 1982 or so. I scanned 3 pages into a .pdf file and made it available so you can download it. The file can be found here and it is the top of the list labeled 567 Tone Decoder CKTs. It is in a zip folder so just download the file to a location of your choice and then right click the downloaded file and choose Extract. Open the folder you extract and there are 3 pages (one pdf) of 567 circuits and examples of what the chip does. That should get you going and understanding things.

Please note that credit for the circuits is presented in the link.

Ron

 

[Hero999]

Is that your site? Looks quite good.

 

[Reloadron]

Is that your site? Looks quite good.

Thanks Hero and yes. Actually it is a disaster long overdue for cleaning up. In reality it is used mostly for behind the scenes experiments and server storage. I have had that domain for maybe 8 to 10 years. About every 5 I blow it away and rebuild the whole thing. However, thanks for the compliment.

I hope the pdf files help.

Ron

 

[SGC622]

thanks guys i'll apply what you have showed me and post back my results. it seems i can learn alot from your website alone.