Experiments 1.1: Introductory Power Supply Circuit

okay first thing we want to do before we get started just to talk about the breadboard for a second now here's a typical breadboard you can see it's made up of different columns and rows and the columns here are joined together so for example at number one we have five pins that are connected together and then we have a break in the center well we took the Gate Bridge chips across the ground and then we've another set of five pins that are connected together to each other as well so

a ter connected together and f2j are connected to go along with this we have two rails two rolls and the ground rail and the +5 volts rails what we're going to use them for you will know if you start on on some horses there's a gap here and it just breaks the rail lines you'd have two different rounds so in our case we want to build our

circuit

so that will connect we're going to use both sides of this rail so the first thing we're going to do is just connect a bridge those

two gaps with there with a couple of interconnecting wires so press that little wire there okay so now we've bridged the two connections and now we want to set up our circle so we set up our

circuit

in the in the corner here so zoom in a little bit to do this now we're going to use a 9-volt battery it's just a normal 9 volt battery DC

supply

and we're going to use a connection cap it's just a cap that goes on tonight volt battery and term 8 some two leads and we're also

going to use a voltage regulator to set up it in this case we're using an LM 0 5 and the LM 0 5 will accept a

supply

DC

supply

and output around 5 volts the this chip is is organized so that it gives us our our pins are as follows the this pin here at the leftmost pin is our voltage in the middle pin is our ground pin and the rightmost pin here is our our voltage out our 5 volts

supply

AB so we're going to connect that up into our

circuit

and we're just gonna plug it in somewhere

like this if we were to plug it in this way for example we have problems on our breadboard because we'd be bridging all three pins will be connected and tied together so we've connected in this way and it means that each one of now pins that we're talking about it pins 1 2 and trade and so pin 1 again is voltage out into his ground and pin tree is voltage in so we just take our cap and connected so the pin and tree I'm going to connect into pin 3 now with our

supply

positive and

pinned to with our with our ground we're gonna connect our pin 2 to our ground rep and I just want to go over a little bit because I know that pin one is gonna have to be connected to plus 5 volts wrap okay so now having connected to super ash that's our that's our

circuit

setup when I connect into

supply

circuit

is hopefully fully working but it's difficult enough trying to make sure that the connections don't that the naked cable isn't touch off each other so we

can't really see anything we could measure what our voltage

supply

our voltage meter router and measure our voltages so take your multimeter and set it to DC voltage and if we set it to 20 volts here we should be fine to measure so we should be able to measure now our input voltage so this should be around nine volts so we make sure that we get eight point three six volts which is what you would expect from the battery and we should be able to see downer our

supply

and what do we get now

this we've got a regulated

supply

well you should see that it's about four point nine six nine seven volts so it means our voltage regulator is working perfectly now it's hard enough to seat us because we of the way our

circuit

is set up so we're going to do is we've got a connection a little LED to indicate when our eyes on our

circuit

is supplied so we're just choosing a green LED and the specification for this LED is that this a it expects to 3 volts maximum and a

roughly current about 232 20 Millions and so when our LED we see that we've two two legs one leg is longer than the other the longer leg is the anode and that's the positive leg and the shorter leg is the cathode and that's the negative leg you'll also notice if you look very carefully at the plastic housing of the LED that there's a little flat area here at the top and that indicates that that's the negative or the cathode so we want to connect this up so I've

disconnected the battery from this

supply

and I'm just going to connect it in so that again the longer leg is the positive leg so we're going to connect the - in here - so I've connected it to the positive rail oops and I've connected the and the negative leg to pin four so that's not connected to anything we need a we need to choose a suitable value for resistor so as I said the the LED had a maximum I expected a maximum voltage of 3 volts which means that we need to drop 2

volts to our resistor to ensure that the 5 volts

supply

is divided in that ratio so 2 volt drop 5 volts

supply

means that we need a 100 ohm resistor so we plug our 100 ohm resistor in across and we need to plug it from the the grand Rev into our in Row 4 ok it's gone in and just make sure that it's not shorting out with the positive pin of the of the led okay so just keep the gap there and we connect in our

supply

and we should see when we do our LED light source so this indicates then

that tells us straight away that our our

supply

is connected and that our batteries and flash and so on so we know that our

circuit

is working correctly so that's our that's our first

circuit

and you want to leave that set up on the board it's it's it's using up a small it's a bit of space in the board but it allows us the rest of the space in the board now to connect up the rest of our

circuit