1 00:00:00,008 --> 00:00:06,916 Welcome back. We're, we're going to start a couple of 2 00:00:06,916 --> 00:00:13,300 lessons on real applications, and we're going to show some lab demos. 3 00:00:15,130 --> 00:00:19,222 And these lab demos fit in a kind of nicely end off this whole module because 4 00:00:19,222 --> 00:00:25,038 we're looking at particular applications. And the applications are going to be 5 00:00:25,038 --> 00:00:29,920 sensors, physical sensors in other devices, in other applications. 6 00:00:29,920 --> 00:00:33,270 And how resistive resistors are used in those sensors. 7 00:00:35,410 --> 00:00:38,735 Let's define a sensor. A sensor is a device that converts a 8 00:00:38,735 --> 00:00:41,516 physical quantity to an electrical signal. 9 00:00:41,516 --> 00:00:45,359 Number one, it convert physical quantities to electrical signals because 10 00:00:45,359 --> 00:00:50,283 we want to be able to record them we want to be able to data log them. 11 00:00:50,283 --> 00:00:54,248 Or perhaps, we want to be able to use that information to control something for 12 00:00:54,248 --> 00:00:59,050 example the engine speed of your car based on an oxygen sensor. 13 00:00:59,050 --> 00:01:03,392 Or maybe the, the temperature in a room based on the thermostat reading. 14 00:01:03,392 --> 00:01:09,760 There are some very typical variable resistors that are used in sensors. 15 00:01:10,990 --> 00:01:15,215 And they're ones that resistance varies, again, is the, since their physical 16 00:01:15,215 --> 00:01:19,234 quantity varies. So, piezoelectric resist, piezoelectric 17 00:01:19,234 --> 00:01:23,812 resisters, when that, where the resistance goes down as pressure goes up. 18 00:01:23,812 --> 00:01:29,630 And in, and this case, in a lot of these cases the relationship is not linear. 19 00:01:29,630 --> 00:01:32,497 So, the resistance goes down in a non-linear fashion as the pressure goes 20 00:01:32,497 --> 00:01:35,768 up. A thermister is a resistor that the 21 00:01:35,768 --> 00:01:39,700 resistance goes down as temperature goes up. 22 00:01:39,700 --> 00:01:44,290 In a strain gauge, the resistance goes up as a strain gauge elongates. 23 00:01:44,290 --> 00:01:48,780 And a strain gauge is just a simple device that can stretch. 24 00:01:50,750 --> 00:01:54,509 A potentiometer is a varying resistor that varies with position. 25 00:01:56,920 --> 00:02:00,500 So then, the lab demo is variable resistors used in sensors. 26 00:02:02,560 --> 00:02:07,246 Looks like it's physical resistance resistors that vary their resistance 27 00:02:07,246 --> 00:02:13,328 based on some physical quantities. This particular resistor varies it's 28 00:02:13,328 --> 00:02:19,080 resistance based on pressure. At the end right here is a circle. 29 00:02:19,080 --> 00:02:23,530 Inside that circle, there are, there's some pressure sensitive ink. 30 00:02:23,530 --> 00:02:27,790 And you can see a, in the outline here, there's a circuit that goes to that 31 00:02:27,790 --> 00:02:34,524 pressure ink, through it and back. Now I want to hookup my leads, my ohm 32 00:02:34,524 --> 00:02:39,835 meter to these leads. These leads coming out of the sensor out, 33 00:02:39,835 --> 00:02:45,854 out of this device, okay? Now let me try that. 34 00:02:45,854 --> 00:02:56,675 I'm going to start pressing on this. And I'm going to be increasing my 35 00:02:56,675 --> 00:03:01,590 pressure. You see it it's like 10 megohms. 36 00:03:01,590 --> 00:03:08,818 As I increase the pressure down to 5, 4 megohms, 3, really pressing hard now. 37 00:03:10,830 --> 00:03:14,490 I'm down to 1.8. It's about as hard as I can press very 38 00:03:14,490 --> 00:03:17,446 easily on this. And you saw, so as I increase the 39 00:03:17,446 --> 00:03:22,280 pressure, the resistance went down. Let me go in the other direction. 40 00:03:22,280 --> 00:03:25,760 I'm going to start loose, letting up on the pressure here. 41 00:03:25,760 --> 00:03:34,206 And it's going 5, 6, 8, 10, 11, 13. So as I decrease the pressure, the 42 00:03:34,206 --> 00:03:39,396 resistance went up. So, that's an example of a physical 43 00:03:39,396 --> 00:03:43,390 resistor that changes its resistance based on a physical property. 44 00:03:45,180 --> 00:03:48,464 Another very common one that you see is called a Potentiometer. 45 00:03:48,464 --> 00:03:53,300 It's a Potentiometer here, this is a round one, a rotary one. 46 00:03:53,300 --> 00:03:59,410 Let me go ahead and hook up. I put alligator leads on here. 47 00:04:18,330 --> 00:04:21,750 This is a resistor that varies its resistant based on angle. 48 00:04:21,750 --> 00:04:33,140 So, it starts with about about 0.2 ohms. And as I change the angle, you can see 49 00:04:33,140 --> 00:04:39,633 that the resistance is increasing. The larger the angle, the larger the 50 00:04:39,633 --> 00:04:46,420 resistance. All the way up to maximum 9.6 kilo ohms. 51 00:04:46,420 --> 00:04:50,727 So from zero all the way to 9.6 kilo ohms based on the angle that I rotated 52 00:04:50,727 --> 00:04:57,620 through. So we see that these resistors, we, we 53 00:04:57,620 --> 00:05:02,604 can vary resistance with respect to these physical quantities. 54 00:05:02,604 --> 00:05:07,350 But the problem is, I can't use resistance in a measurement system. 55 00:05:07,350 --> 00:05:11,969 I'm using resistance here. I'm measuring resistance with my ohm 56 00:05:11,969 --> 00:05:15,590 meter. But what most measurement systems need is 57 00:05:15,590 --> 00:05:19,265 a voltage. So, I would like to convert this change 58 00:05:19,265 --> 00:05:24,726 in resistance into a change in voltage. Because voltage is something that I can, 59 00:05:24,726 --> 00:05:27,780 I can use. I can input to my system. 60 00:05:27,780 --> 00:05:32,370 So, let's convert this, try to convert this Potentiometer into a sensor. 61 00:05:32,370 --> 00:05:38,060 Looking at the schematic here, I'm building this circuit. 62 00:05:38,060 --> 00:05:41,860 Here's my potentiometer just by itself. And I built the circuit around it. 63 00:05:41,860 --> 00:05:44,815 So, I put this what we call biased voltage across it. 64 00:05:44,815 --> 00:05:50,095 And usually, we'll pick, like 5 volts or 10 volts constant voltage around it. 65 00:05:50,095 --> 00:05:54,666 High on one side, low on the other. And we have a pick off point and this is, 66 00:05:54,666 --> 00:05:59,590 in this particular case, it's, it's the additional lead that I had. 67 00:05:59,590 --> 00:06:03,244 I can move this pick off point up or down, and the way I move it up or, up or 68 00:06:03,244 --> 00:06:09,887 down is by changing the position. Let's, let's look at this schematic over 69 00:06:09,887 --> 00:06:13,190 here. It's the same schematic. 70 00:06:13,190 --> 00:06:17,902 Oftentimes we do that, as long as I've defined a ground, then this point is a 71 00:06:17,902 --> 00:06:23,476 potential of this many volts with respect to ground. 72 00:06:23,476 --> 00:06:26,548 The reason I wanted to show it this way is it's a little bit more clear that this 73 00:06:26,548 --> 00:06:31,348 is a linear Potentiometer, a slider. A slider meaning that I take the pick-off 74 00:06:31,348 --> 00:06:35,774 point, and I slide it up or down. So I'm, could be picking off down here, 75 00:06:35,774 --> 00:06:40,106 or here, anywhere along this point. If I pick off down here, I should be 76 00:06:40,106 --> 00:06:43,558 getting zero voltage because I'm grounded. 77 00:06:43,558 --> 00:06:50,677 As I start moving up higher, then the percent of the total resistance that is 78 00:06:50,677 --> 00:06:58,050 below my pick off point is larger. This is the voltage divider law. 79 00:06:58,050 --> 00:07:05,986 The larger the percent of resistance that I'm, I'm measuring, the larger the 80 00:07:05,986 --> 00:07:11,680 voltage will be. Now over here, I have distance marked. 81 00:07:11,680 --> 00:07:14,080 And this distance can be meters, millimeters. 82 00:07:15,110 --> 00:07:19,816 That's measured y at being some distance. If my pick off point is here, my distance 83 00:07:19,816 --> 00:07:23,690 will be zero. And the larger the voltage is and the 84 00:07:23,690 --> 00:07:27,530 more I move that slider up, the larger the distance is, the larger the voltage 85 00:07:27,530 --> 00:07:31,793 is. So in other words, my voltage that I read 86 00:07:31,793 --> 00:07:38,002 is proportional to this distance. Let's look at a, an angular type of 87 00:07:38,002 --> 00:07:42,010 potentiometer. Sometimes we call it a heliopot. 88 00:07:42,010 --> 00:07:45,706 The one that we had, that I showed you before, actually went around more than 89 00:07:45,706 --> 00:07:50,018 360 degree turns. But you can see, and say, I put it at the 90 00:07:50,018 --> 00:07:55,954 lowest mount, I get zero voltage. And as I increase this angle, then I get 91 00:07:55,954 --> 00:08:01,580 a larger, and larger voltage until I reach the maximum voltage. 92 00:08:01,580 --> 00:08:06,182 And if I want to look at this sensor, going back to this, I want to convert 93 00:08:06,182 --> 00:08:10,890 this, it, this Potentiometer into a sensor. 94 00:08:10,890 --> 00:08:13,060 So I need to hook it up to a power supply. 95 00:08:13,060 --> 00:08:18,300 This lead is for a five volt power supply. 96 00:08:18,300 --> 00:08:25,433 That's the ground on it. And I'm going to match that with the 97 00:08:25,433 --> 00:08:33,382 ground on digital voltmeter. And, and this is the other end of the 98 00:08:33,382 --> 00:08:38,698 lead. So, I've given it a plus 5 voltage power 99 00:08:38,698 --> 00:08:43,974 supply. And this is my pick off point. 100 00:08:43,974 --> 00:08:52,895 We convert that to volts. [NOISE] So, now I'm measuring voltage. 101 00:08:52,895 --> 00:08:58,890 If I start out with the smallest angle, and I start increasing angle. 102 00:08:58,890 --> 00:09:05,697 I now increase the voltage. So when I get about half way, this is 103 00:09:05,697 --> 00:09:10,440 about halfway. The halfway angle I get half the voltage. 104 00:09:10,440 --> 00:09:17,050 And as I keep increasing this, then I get up to the maximum voltage. 105 00:09:17,050 --> 00:09:21,550 Now, you can imagine instead of this being a screwdriver, maybe this is a 106 00:09:21,550 --> 00:09:26,280 lever, maybe there's a customer turning a lever. 107 00:09:26,280 --> 00:09:29,720 And you want to see well where did they, how far did they turn the lever? 108 00:09:29,720 --> 00:09:33,780 You can use a Potentiometer to measure that, or somebody's turning a dial. 109 00:09:33,780 --> 00:09:37,290 And you want to see how far they've turned the dial. 110 00:09:37,290 --> 00:09:42,416 Well, use a Potentiometer. You can even use this on a motor shaft to 111 00:09:42,416 --> 00:09:48,234 see what the angle of the motor is. And that's how we can convert a variable 112 00:09:48,234 --> 00:09:54,136 resistor into a sensor. To summarize, resistance often varies 113 00:09:54,136 --> 00:10:00,858 with physical properties. Sensor utilize this property to convert 114 00:10:00,858 --> 00:10:05,040 physical quantities to voltage. And then, we use those voltage signals to 115 00:10:05,040 --> 00:10:09,870 record the data or to be able to use it to control other systems. 116 00:10:12,260 --> 00:10:16,352 In the next lesson, we will use a Wheatstone Bridge as an application to 117 00:10:16,352 --> 00:10:22,932 build a particular type of sensor. Nathan and I will see you online in the 118 00:10:22,932 --> 00:10:23,570 forum.