Help With Building Low Voltage Relay For School

[DoktorD]

Hi guys,

I had a thread in the robotics section on this, but it seemed like I put it in the wrong place. They helped me get to this point... I need to make or find a low voltage solid state relay.

Heres what I'm trying to do... I'm trying to make my ipod control a 12V DC motor. If I play a constant tone on the ipod with the volume all the way up, I get a constant reading of 79.5 mA. The robotics guys got me to realize that the voltage of the ipod is not enough to trip a normal relay switch.

And yes I'm aware of other methods like sound switches and things, but if I can get this to work, I'm going to stay away from that

Soooo...

Well find a DC relay that activates directly on 1ma at 1-2 volts dc or so and we can see what we can do for you. I found

I found THIS page where a guy made a low voltage solid state relay tripped by his MIC jack... That should work for my application, right?

**broken link removed**

Now, please understand I'm only a senior in High School with VERY little electronics background.

If I do make this, should I use the same parts and resistors used in the instructions? It seems like it should all be the same, the relay would just power a small 12V DC hobby motor.

 

[ljcox]

That won't do what you want.

What you need is a "voice activated switch". I suggest yoiu do a search of this forum for that phrase. I think there have been several discussed in the past.

In essence, what you need to do is
1. rectify the audio signal
2. smooth and amplify the resultant DC signal to drive a relay.

 

[Leftyretro]

Here is a circuit showing the sections needed for a sound activated switch. There are simpler circuits I'm sure but this one shows the various stages reguired Input amp, rectifier/filter, comparator, relay driver.

Lefty