Amplifying Signal with Transistor and Relay basics

Discussion in 'The Projects Forum' started by Chris15, Mar 28, 2010.

  1. Chris15

    Thread Starter Active Member

    Apr 15, 2009
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    Hello
    i have a previous thread on this but the reply's have stopped it is called 'Wireless Remote Controll'
    My Problem:
    I have a signal coming out of a doorbell output (speaker wires) it is about 2V roughly and can liight an LED, retched told me that if i used a transistor to boost the voltage from the output, then used a LATCHING RELAY i could acheive what i previously tried in my doorbell christmas light problem.

    I done some research on these new type of relays and now know they have a cam mechanism, so that when one pulse of power is applied they will 'click' and that power can then be turned off and the relay will stay as it is, and when the same pulse comes back, it will energize the coil and un 'click/ latch' the relay which is perfect for what i need.


    I Need:
    • Some sort of wiring diagram of these LATCHING RELAY's on how to use them, the sort with 2 coils, to get the result i have explained.
    • A simple lecture on how to use a transistor to aplify the voltage,
    Note: If i canno't boost the voltage to 8V which is the specified voltage needed in my jaycar link in the origonal post i can simple use one normal relay SPDT and then power the Actual Relay

    Thanks, Chris
     
  2. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    I took a quick look back at your earlier post...and I'm going to make some assumptions.
    1. With the speaker removed you get a 2v output. Because this was a speaker, I'm going to assume that the output is AC or pulsating DC. (Can you verify which?)
    2. The speaker output was some series of pulses...Biiiiing or Biiiiing-Boong (sorry, best I could do)
    3. You can provide an external DC supply for the switching circuit. (a wall wart?)

    The attached is a modified version of one I did, to have the output of an alarm clock buzzer change states of a relay. In this case the connections on the left go to your speaker connections. D1 provides positive pulses to the transistor Q1. Q1 triggers a re-triggerable monostable U1. U1's output stays high slightly longer than the chime sounds. The monostable triggers a flip flop U2. U2 drives the MOSFET Q2 that drives the relay.

    The component values are for my alarm. You would probably have to change the values of R8 and/or C2 to fit your chime timing. If the speaker output was AC (through a coupling capacitor) you would need a resistor across the speaker connections.

    This is just an idea.

    Ken
     
    Last edited: Mar 28, 2010
  3. Chris15

    Thread Starter Active Member

    Apr 15, 2009
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    Thank you Ken a bit more complex than i had expected but thats ok, because after reading retched's post it seemed like all i needed to do was use a latching relay and a transistor to amplify, but i beleive you more as he stopped replying and you have helped me before.

    Ok now i am assuming the speaker output is AC because if i connect an LED (Red 5mm) it will fully light but if you look close it will flicker to the sound of the music, but when i connect my multimeter it shows 2.73V constantly and after the chime has finished it will go back to Zero. i tried connecting a relay and a 1.5V battery in parallel with the output but had no luck. I like you Circuit and it is not complex at all just some wiring but before i build your circuit which i know will most likley work i want to ask a question about the latching relays.

    I understand that they have mechanics inside them with a cam mechanism that goes like this, it says if you apply one pulse the relay will flick and stay where it is without any more power, and if you apply the same pulse to the same wires in the relay will then unlatch, so thats where i thought that if i connected a transistor it would apply enough voltage to click the relay, or maybe i could create a circuit with a charged capacitor or something and once a small amount of voltage (2.73V) for example it will discharge the cap into the relay contacts just enough to flick it.

    Sorry if this complicates things further

    Chris
     
  4. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    Chris,

    With that info, I think my circuit will work for you. If you can find a single-coil toggling (bistable) relay you might be able to replace the circuit after the 555.

    It might even be possible to eliminate the 555, it would depend on the relay and music pulses.

    A quick search indicates the impulse/stepping relays are in the $30 range.

    Ken
     
    Last edited: Mar 30, 2010
  5. Chris15

    Thread Starter Active Member

    Apr 15, 2009
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    Ok i will give your circuit a try its just that all of the circuits i have made are on the practice boards with the holes and i just use jumpers so i thought i should start making PCB's so i think your circuit may be the first thing i have done it with

    (i have made many PCB's before but that was at school with the bubble machine and the UV light i dont have them so i think the paper you can iron on is maybe pretty good)

    Chris
     
  6. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    Another possibility is to use pref-board that has solder pads on the back. Solder in your components and do point-to-point wiring with 30ga Kynar wire-wrap wire soldered between pads. The attached is an example, though on a board with power bus strips. For simple circuits, I do most of my one-offs and prototypes this way.

    Ken
     
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  7. Chris15

    Thread Starter Active Member

    Apr 15, 2009
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    Ok thanks i will have a look around jaycar for different types of practice boards, and get some 30 gauge kynar wire

    Just a curiosity question, how would i amplify the voltage from a component with a transistor?

    Chris
     
    Last edited: Apr 2, 2010
  8. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    Take a look at my schematic in post#2. R5,Q3, and R8 form a "common emitter" amplifier that can amplify a small signal (>0.6V) on the input to a large signal (12V) on the output.

    You might want to look through the tutorials in the links at the very top of this forum. Vol.III Chapter 4 has info on simple transistor amplifiers.

    Ken
     
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  9. Chris15

    Thread Starter Active Member

    Apr 15, 2009
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    Thanks, i have always wondered at the start of Electronics class at school how a little component could get more volts with the same supply. i have posted a new thread on another problem that may be answered by this simple transistor but it is maybe more complex, thanks for solving this problem.

    Thanks, Chris
     
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