Replace speaker of alarm clock with dc motor

Thread Starter

sadiq3210

Joined Jun 14, 2013
26
Can you measure the DC and AC voltage coming from the speaker wires? Does this go to zero when the alarm is off?
Is this alarm a tone or from a radio?
If you can use a separate battery then you can likely use a transistor amp to turn on the motor.
crutschow

when alarm is off, there is not voltage (0 dc voltage) across speaker wires.
when alarm is on, it start beep, then another type of beep, and then last type (loudest) type of beep.
when alarm starts, the voltage starts increasing and continuously fluctuating.
the voltage is different when speaker is connected, and when speaker is not conected.
when alarm is on and mulimeter in connected to terminals then if i put fingers on the terminals of multimeter, the voltage rises to around 0.75 , i don't know why
 

Thread Starter

sadiq3210

Joined Jun 14, 2013
26
Can you measure the DC and AC voltage coming from the speaker wires? Does this go to zero when the alarm is off?
Is this alarm a tone or from a radio?
If you can use a separate battery then you can likely use a transistor amp to turn on the motor.
do you want the video of the voltage from multimeter?
 

Rich2

Joined Mar 3, 2014
190
Use a full wave bridge rectifier then a 1000 ohm resistor then a smoothing capacitor (say 47uf?) onto the base of an NPN transistor (bc337 maybe?) put the motor between the collector and new power supply and emitter to ground . Ground the negative speaker wire too
 

crutschow

Joined Mar 14, 2008
28,197
Use a full wave bridge rectifier then a 1000 ohm resistor then a smoothing capacitor (say 47uf?) onto the base of an NPN transistor (bc337 maybe?) put the motor between the collector and new power supply and emitter to ground . Ground the negative speaker wire too
No. You don't what to ground the speaker wire from the clock if it is also going to the bridge. That will short out the bridge.
 

EinarA

Joined Sep 13, 2014
5
On Rich's circuit, it would be much better to use a voltage doubler than a bridge. Place the resistor between the filter cap and the transistor base. A capacitor on the base never develops much voltage and it is drained away almost immediately.
 
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