Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

audible signal to switch?

Status
Not open for further replies.

Anthony Mariana

New Member
How would you convert an anolog signal into a on/off switch?a little background. i would like to use a metal detector (hobby type) on a conveyor system. when metal is detected i would like it to signal and shut down the conveyor. aside from the speaker there is also a headphone plug.

I was told that this was easy
The simplest way would be to use a LM339 comparator IC.:

To reduce the interference element, the speaker headphone would be preferable to use.

A small diode bridge would be used to bring the audio signal all in positive territory. A small capacitor could be used to smooth the "DC" signal (not too big a capacitor or the response time of the system might become to slow. With LM339 and a little variable DC level (a knob on a potentiometer), you could be able to set the sensitivity.

You will need something to latch that metal detection. That can be made with logic gates: Or with relay logic.
If you don't implement a latch, the conveyor may start right after it detected something, barely slowing down.

Problem....Can anyone show me how they connect ? Thanks
 
Audio detector and latching comparator. Close switch momentarily to reset it once tripped. As shown, it detects about 6 cycles of a 2Vp-p 1kHz sine input.

If you can tell me what the frequency/amplitude of your tone burst is, I can optimize it for that.
If you need to drive a relay or some other load, a buffer may be needed. The "LatchedAlarm" output signal is not suitable for driving a relay directly.
 

Attachments

  • Draft3.gif
    Draft3.gif
    60 KB · Views: 157
Last edited:
Audio detector and latching comparator. Close switch momentarily to reset it once tripped. As shown, it detects about 6 cycles of a 2Vp-p 1kHz sine input.

If you can tell me what the frequency/amplitude of your tone burst is, I can optimize it for that.
If you need to drive a relay or some other load, a buffer may be needed. The "LatchedAlarm" output signal is not suitable for driving a relay directly.

This is an interesting idea!

On another note i dont mean to steal the topic away and go off on a tangent... but Mike what program did you do this schematic and simulation in?

Thanks

-Ethan
 
U1 is a generic comparator/opamp, but it is a good representation of a LM339.

The program is the free LTSpice (search these forums or google it)

You need to determine the minimum amplitude (Vp-p) that you want the circuit to respond to. If is less than 2Vp-p, we may have to add an opamp amplifier ahead of the rectifier.
 
You might also want to consider Schottky diodes which will also improve the sensitivity.
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top