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### Course: Electrical engineering>Unit 9

Lesson 1: Household items

# What is inside an alarm clock radio?

In this video we explore what is inside an alarm clock, how it is made, and how it works. Created by Karl Wendt.

## Want to join the conversation?

• @ Did they mold the buttons into the housing at the same time that the molded the radio casing? I guess I'm asking is it possible to mold different materials which require different temperatures in the same mold?
• Yes the buttons were molded at the same time as the housing. It is possible to co-mold or multi-shot mold different materials in the same mold. See the following links for examples:

• So, with step-up transformers, does an increase in voltage mean a decrease somewhere else, perhaps the current? And in step-down transformers, does a decrease in voltage affect the current? And if so, does it cause an increase in current? And if that's is the case, is that higher current dangerous for the alarm clock's components or is the alarm clock built to handle it?
• Yeah it is constant , neglecting the power waste
• What is a transformer?
• A transformer is very common electrical component that is used to change the voltage and current of an AC power source like wall outlets.Transformers are made of at least two coils of wire usually wrapped around a iron core. The size difference between these coils determines how much voltage and current is decreased or increased.
• What is Reverse Engineering?
• Reverse Engineering is taking something apart to , find out how it works , and to learn from it. It has many possible applications including but not limited to ,warfare , ancient civilizations , and last but not least education.
• how does the electricity chose which path to travel along the circuit board if there are multiple paths of copper?
• Most times there is only one path. Sometimes an integrated circuit (IC) or a transistor can split up the circuit.
• Anyone know the details of how the capacitors near the power input () actually smooth out the DC power supply?
• Tedz0r,
It's the process of from converting from AC to DC where the smoothing out happens. The video explained fairly well what the diodes do- basically diodes only allow current to pass through in one direction. So that's how the sine wave gets split. 4 diodes are wired to the AC input in such a way that 2 of them only allow the positive direction through, and 2 of them only allow the negative direction through. Then, they are wired back together in such a way that all of the current is flowing in the same direction on the other side-- think of that as basically taking the 2 negative-passing diodes and wiring the output backwards from the positive passing diodes so that all the outputs are now going in the same direction. That isn't exactly the way it works, but a good analogy. This is called a "bridge rectifier."

So now we have a power source that goes from 0 to some maximum positive amount and back to 0, over and over again. In this case the maximum is 9 volts (since the transformer stepped the voltage down to 9). But what we would like is a constant flow of power. So what we are going to do is use a capacitor. Think of a capacitor like a little tiny battery that can be charged and discharged very quickly. Imagine we only use half of our 9 volts, or 4.5 volts, to run the device. In that case, whenever the bridge rectifier is putting out greater than 4.5 volts (which it is doing half the time), we use the extra to charge the capacitor. Whenever the bridge rectifier is outputting less than 4.5 volts (again, half the time), the capacitor stops charging and starts discharging-- providing that extra power that the bridge rectifier is no longer powering directly. When the bridge rectifier is outputting 0 volts, the capacitor is outputting the maximum voltage, 4.5 volts, so the device always sees a (relatively) constant voltage, of 4.5 volts. By the time the capacitor is completely discharged, the bridge rectifier is outputting more than 4.5 volts again, and is ready to power the device plus recharge the capacitor.
• If I had a random antenna, would it pick up radio waves even though
it isn't connected to any filters or inducers?
• I would pick up radio waves but there would be no way to know what they mean unless the antenna is connected to something.
• THIS IS AWESOME, COULD YOU TAKE A PHONE APART NEXT?!
Because if someones phone isn't working you can just help 'em fine out what's wrong, Right?
• Hello again Tess.

I'm glad to see you are still researching electronics.

There are many "teardown" videos on line. One of my favorites is David Jones. Here we see him teardown a defib machine: https://www.eevblog.com/2016/08/11/eevblog-909-heart-defibrillator-teardown/

Fixing a cell phone is a near impossible task. Even experienced service technician would have a very hard time. The components are beyond small...

Here is another excellent series of videos about computer and cell phones: https://www.youtube.com/channel/UCl2mFZoRqjw_ELax4Yisf6w

Caution - some of these personalities have strong language but the content is excellent.

Regards,

APD