I need a circuit to run a vibrator/motor in my TX.

[HankF]

I can't hear my Futaba's beeper (hearing impaired) and I want to pick up the beeper tone and have it run a vibrator/motor like those used in pagers. motor/vibrator.com has 2 - 3 vdc units and I'm thinking that a single transistor biased at cutoff with the input being connected to the beeper transducer and the output connected to the vibrator/motor should work.

What transistor would work?
How should I isolate the input from loading the beeper and how do I reduce the output from a 9.6v supply down to the 2-3 volts of the vibrator/motor.

Any help would be really appreciated.

Hank

[BMatthews]

First off you should probably check to see if the signal to the beeper is actually DC rather than pulsing DC. The transducers are often similar to watch types and they are actually fed a chopped DC at the tone frequency. If this is the case in your transmitter then you'll have to pass that signal through a signal diode and use a capacitor on the output too hold the voltage before it goes into an emmiter follower transistor that prepares the change for your cutoff biased second transistor. It's been a while but the emitter follower has a very high input impedance as long as there's a fairly high resistor in the emitter lead. The input resistance being the gain times the emitter load.

As for the supply to the motor you could make up a little regulator circuit to run off the TX battery but it may be easier to just put in one or two alkaline batteries in a holder. Used this way it'll last for most if not all of the flying season.

[Felix Althaus]

Hi

As for the supply to the motor you could make up a little regulator circuit to run off the TX battery but it may be easier to just put in one or two alkaline batteries in a holder.

Or you can put a couple of diodes between the motor and the TX battery, so you have a voltage drop of about 0.7V per diode.

To choose a transistor you should kow how much current the motor draws and then choose a transistor which can sustain that current (I think a 200mA type or so should be enough..)

I would recoomend to put a small cap (perhaps 100nF) between the motor connectors.

mfg
Felix

[zagisrule!]

Perhaps a small N-chan MOSFET would be a better choice, the 2N7000 is rated to 800mA (If I recollect correctly)