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Current time:0:00Total duration:13:54

What is inside an alarm clock radio?

Video transcript

okay so today we're going to take a part in alarm clock radio we're going to see what's inside it and how it works there's basically four systems that we're going to evaluate there's the power system there's the alarm clock or the the clock itself and the the structure of the device and in the interface and then we're also going to take a look at the the radio so the first thing is let's take a look at the power system so I've already cut apart this plug here and you can see the prongs that's where the power comes from and we've got the the two wires here the two wires connect to what's called a transformer now in the transformer there are three key components so we've got a primary coil a secondary coil and an iron core now the primary coil is wound around a certain number of times the secondary coil is wound around fewer times in this particular transformer so that means it's a step-down transformer what this transformer does is it converts 120 volt 8 AC down to 12 hour down to nine volt AC so that the because the components in the alarm clock need lower voltage so it steps the power down now the way it does it is this coil induces a current flow in this coil and the iron core helps to help that to happen because this coil has fewer turns it's a step-down transformer which means that the voltage is less coming out of this part now if there were more turns it would be a step-up transformer and the iron core again facilitates that that process it's called electromagnetic induction this coil induces a current flow in this coil so anyway the power travels through the cable here the the wire and it comes to the alarm clock so let's take a look at the housing first of all it's a it's fairly low-cost housing it's made out of injection molded plastic so let's see see what that power comes in and where it goes so one of the ways they've been able to reduce the cost of this is they basically just only use one fastener one one separated fastener so this is a screw and the more screw you have in things the easier they are oftentimes to put together and take apart but they are also more expensive every screw requires either a robot or a person to assemble it and it's an expensive cost adder so the more screws you can take out the more costs you can reduce and so all these fasteners in this are actually molded into the body panels so here's a there's a pin or a tab there so we can pull this top part off now this part right here is the is the front plate or the the front bezel it's made out of a tinted acrylic and it's injection molded there's two parts of the mold that come together a multi plastic is injected and then this comes out the reason its injection molded is that it creates a very precise part you can get a nice clean finish and when you produce them in high volumes you can do it for very low cost so there's that and the the the reason it's tinted is that it hides the interior components except when the bright lights still show through okay so this is the inside so let's take that part out see if we can get that there there we go so that's it's all together and and and part of the way they've kept the cost low again is there's not a lot of separate pieces that they have to assemble there's one module they can just plug in to this housing so let's take a look at the housing before we get back to the power system so the housing was made out it was injection molded it's three parts of a mold so there's one part that comes in here one part that comes in here and then there's a core that goes in here so why one of the ways they've been able to reduce the cost is by molding the buttons into the housing so there's a little surround around the button and that surround is basically a place where there's no material so it allows the button to flex but there's also little tabs that hold it in place so all the buttons were molded in and when you push on the button it triggers this pin which triggers a switch below we'll get to that in a second in the back you've got a place for your 9-volt battery so your backup battery if the power goes out to slide in so you push your battery in there and this little tab holds it in place and the battery pushes up against these two little wires right here and so very low cost connector for the battery they don't need the you know an extra door housing piece on the outside so again reduces cost now the way this was made you saw how the mold came together the plastic was actually injected right here you can see that little place right there there was a piece of plastic that stuck out once this fell out called a sprue and they broke that off and you can see the remnants of that and um all of the yeah by having all those features molded into this you you reduce cost because you don't have to assemble separate buttons and things like that alright let's take a look at the power again so we'll take this top part off here where all the button brackets and things are unplug this alright so you can see the power comes in right here and if I take that off alright so we have four diodes in an over in a row there and those diodes function as a bridge rectifier so they convert the nine volt AC power that's coming in into DC power so the AC power flows like this it's like a sine wave it's a it's flowing in both directions they convert it and they cut it so that it only flows like that so they take the sine wave and cut it and flip it over so it goes like this and so it's still a little rough it's a little bumpy and so these capacitors help to smooth that power out because these components don't want power that fluctuates a lot they want really smooth consistent direct current and that's what that's what those do and that's how those capacitors can help out so let's take a look at the clock system here so this is our clock divider integrated circuit chip and what it does is it it takes the a signal from a crystal oscillator which is a piece of quartz crystal that's tuned to a specific frequency when electricity is is put into the quartz it it oscillates at a particular frequency and produces a voltage so it gives you a very precise division of time and often times those voltage divisions can be say like 60 Hertz or 60 times a second so then what you need to do is once you have all those divisions you need to be able to separate those divisions into minutes and hours and then send the signal from those divisions in minutes and hours to a display so those divisions come from here they go through the ribbon cable they go to the 7-segment display here and it's called a seven segment display because it has seven different segments and each little piece right there and they display the the minutes and the hours they also there's LEDs here that display AM and PM now LED stands for light emitting diode and it's a very efficient low-cost way to display to display the the time and so that the LEDs are mounted inside this little plastic piece right here and in and inside there there are there's kind of a light conduit which helps to spread the light out so an LED is a very intense the spot of light and so this this housing helps to spread it out so it makes each segment look completely full and and the LED lights up the whole segment there and so on the backside of that is a printed circuit board and that helps to basically direct the electrical signals coming through the ribbon cable to the right 7-segment portion so you know may turn out that it's a you know 630 and so you want only certain segments to light up because of that we have a jumper here which helps to you can use jumpers to alter the functionality of the of the 7-segment display so this one may be program or may be set up to function in a certain way so this jumper allows you to transfer power to a different part of the display and then we have these little white spots here and what that is is the back of this this module the 7-segment module has these little pieces of plastic that stick through and there's a there's a hot plate that basically pushes on those those pins that stick through and melts them and it holds the plate against the printed circuit board and it's just a cheap way or an inexpensive way to fasten things together it works pretty well so that's the the clock portion and the buttons let's talk a little bit about the interface so so the buttons when you push down on the buttons here they trigger these pins and you can see the pins flex pretty good right here so the pins are connected by these little standoffs and because the standoffs are really thin they can flex and so the pin flexes and the pin rests on top of the switch and when you press the button the pin moves and the switch gets triggered so when you want to snooze in the morning you push this it shifts the pin and it causes the sleep button to be triggered and that's kind of how that works this is kind of ingenious in another way too because it holds a bunch of different things together so it's got the pins it holds the speaker and it also holds the ferrite rod with the the copper coil around it which functions as an antenna so that's an antenna for am/fm radio so the signals come from here I got a wire broken their signals come from here and they go to this thing which is a set up of four variable capacitors and they help to tune out frequencies we don't want so when we turn our dial we can go right to 101.1 FM or Fino 5:30 a.m. or whichever station we want this helps us to select those things those variable capacitors help us to filter out unwanted frequencies then these two things they're called inductor coils and they can be used to oscillate at a particular frequency if they're coupled with a capacitor and that can be useful in performing radio functions as well and this guy right here is a it's a radio chip it's an IC chip that helps to demodulate or to separate the the music or the the signal that you want from the actual wave so AM is is amplitude modulation so that means that the wave is is changed in its height and FM is frequency modulation so that means that the wave has changed in its in how often it occurs in order to embed the signal that we get to listen to as as radio sound so this chip basically decodes that and says this is the original wave and then this is the embedded signal and that's able to be then sent to our speaker right here so uh before it gets to the speaker it goes past this variable resistor right here which is also called a potentiometer and so when we turn that it changes the resistance in the circuit and it either increases or decreases the volume and increases or decreases the amount of power running to these wires and this one actually has come undone but so the wires come here and they and there's a copper coil in a magnet and when the powers run to the copper coil and the magnet it causes the paper cone to vibrate and that produces a pressure wave and we interpret that as sound and so that's how that works and then right here you can see there's two different switches here we've got a switch that controls whether we're an a.m. or FM and then another switch that just sort of lets us select different functions like you know turn it turn the alarm clock off or to have it set to buzzer instead of a radio and and things like that and you can also see this right here that's a resistor and that resists electric current flow and that can be useful because it helps to prevent too much power from flowing to certain components on the board and things like that this is a transistor these things or transistors they can function as switches and these guys right here are filters and they can help to reduce noise or electromagnetic interference and they can help to clean up they're probably used in the radio circuit here to help to clean up the signal and on the back here you can see again these prongs connect to the battery and this is the printed circuit board here on the back and that's basically it's a thin layer of copper that's been applied to this fiberglass board and then a chemical was used that they use basically a photo emulsion process which is like a similar - to remove to shine they shine a light on it and they use the photo motion process to remove certain areas of the copper and keep other areas and so they'll use an acid or a material to etch away the areas that aren't protected and those result in copper traces and so those copper traces are basically very well ordered little tiny wires that are very flat and they allow us to connect all these different components in a very small space very efficiently so we can just push the components these are called through-hole components through holes and then solder them on the back and then they're all wired up together and we don't have to worry about a lot of messy wires and things not being connected correctly and you can see there's different components small components on the back the little surface mount resistors and things like that so that's a that's our alarm clock radio and those are the insides hope you've enjoyed it