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 thosetwo 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 DCsupply
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 alsogoing 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
DCsupply
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 voltssupply
AB so we're going to connect that up into ourcircuit
and we're just gonna plug it in somewherelike 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 andpinned 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 intosupply
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 wecan'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 oursupply
and what do we get nowthis 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 ourcircuit
is set up so we're going to do is we've got a connection a little LED to indicate when our eyes on ourcircuit
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 aroughly 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 2volts to our resistor to ensure that the 5 volts
supply
is divided in that ratio so 2 volt drop 5 voltssupply
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 oursupply
and we should see when we do our LED light source so this indicates thenthat tells us straight away that our our