Audio Power to Activate a sensitive Relay

[GerryO]

Hi Folks:
I would like some assistance with the following:
Could someone direct me to a simple schematic that will perform this
function: Take the low voltage audio call tone from a (family radio service
handset) that is heard in the headset and amplify the signal enough to
activate a sensitive a small relay of 9-12 vdc coil drawing 25ma ( the
type normally found on printed circuit boards). What would a circuit that
performs this task be called, so I could do a google search?

Thanks for your help...

Gerry

 

[Lord Garth]

Hi Folks:
I would like some assistance with the following:
Could someone direct me to a simple schematic that will perform this
function: Take the low voltage audio call tone from a (family radio service
handset) that is heard in the headset and amplify the signal enough to
activate a sensitive a small relay of 9-12 vdc coil drawing 25ma ( the
type normally found on printed circuit boards). What would a circuit that
performs this task be called, so I could do a google search?

Thanks for your help...

Gerry

You are looking for a tone decoder...

You will need to know the frequency of the received tone in order to build
a decoder. Although the LM567 IC is quite old and, more than likely, out of
production, they will be available for quite a long time. Look at the data
sheets and we'll see.

 

[Terry Pinnell]

Hi Folks:
I would like some assistance with the following:
Could someone direct me to a simple schematic that will perform this
function: Take the low voltage audio call tone from a (family radio service
handset) that is heard in the headset and amplify the signal enough to
activate a sensitive a small relay of 9-12 vdc coil drawing 25ma ( the
type normally found on printed circuit boards). What would a circuit that
performs this task be called, so I could do a google search?

Thanks for your help...

Gerry

Building on Lord Garth's suggestion, here's a practical starting point
from which you can adapt:
http://www.terrypin.dial.pipex.com/Images/567ToneDecoder.gif

 

[Robert Monsen]

Building on Lord Garth's suggestion, here's a practical starting point
from which you can adapt:
http://www.terrypin.dial.pipex.com/Images/567ToneDecoder.gif

One point about 567s is that I've found they are often difficult to trim
for an exact match of frequency. You need to use a pot, and things can
subsequently drift around. The datasheet is fairly cryptic, as I recall,
giving the values required in a couple of crude graphs, which are
labeled badly.

--------
Regards,
Robert Monsen

"Your Highness, I have no need of this hypothesis."
- Pierre Laplace (1749-1827), to Napoleon,
on why his works on celestial mechanics make no mention of God.

 

[Robert Monsen]

Hi Folks:
I would like some assistance with the following:
Could someone direct me to a simple schematic that will perform this
function: Take the low voltage audio call tone from a (family radio service
handset) that is heard in the headset and amplify the signal enough to
activate a sensitive a small relay of 9-12 vdc coil drawing 25ma ( the
type normally found on printed circuit boards). What would a circuit that
performs this task be called, so I could do a google search?

Thanks for your help...

Gerry

I've recently seen a bandpass filter -> signal using opamps on Bill
Bowden's site:

http://ourworld.compuserve.com/homepages/Bill_Bowden/page4.htm#whistle.gif

It looks to be a bandpass filter into a level detector, and from there
into a solid state relay. This one flipflops (first whistle on, second
whistle off) so you may need to mess with it for your application.

Also, You'll have to fiddle with the filter values to get it to
recognize your tone, unless you are lucky. The computation for the
resistor values required is shown.

--

--
Regards,
Robert Monsen

"Your Highness, I have no need of this hypothesis."
- Pierre Laplace (1749-1827), to Napoleon,
on why his works on celestial mechanics make no mention of God.

 

[GerryO]

25 March 2005 6:08 PM

Thanks a lot for your help guys , I will take your tips into consideration.
I will use the 567 as I have several and my tone is very close to 2 khz.

Cheers...Gerry