## Consider PWM signal When using a microcontroller and want to drive motor control or controlled intensity, you can use DAC to generate an analog output voltage. But there is an easier way of doing this. You can use a digital output to reach the same results. This technique is known as PWM -Pulse Width Modulation. In this picture, you can see a 50% duty cycle square waveform. The width of ‘0’ is equal to the ‘1’ level. This means if the signal amplitude is 5V, then the average voltage over one cycle is 2.5V. It is as though of hawing constant 2.5V voltage.

## K-Type Thermocouples reviewed A thermocouple is a sensor that generates an electrical potential related to the temperature. The sensor’s operating principle is based on the fact that any electrical junction between two different metals generates an electrical potential that depends on the temperature and the metals used. The principle applies equally well if three metals are used. In that case, there are two junctions in series and the net potential results from the series addition of the two individual potentials. For example, if a copper iron junction is in series with an iron-tin junction, the net potential is the same as for a copper-tin junction. However, that is only true if both junctions are at the same temperature. The K-Type thermocouple is usually made of Chromel (+) and Alumel(-). The voltage generated from this sensor is 4mV/100°C. The max temperature that can thermocouple withstand is 1000°C without any damage.

## Impulse signal distortion in the transmission line Today most electronic equipment consists of signal generators and processing units. These units are connected with transmission lines. These lines have a big influence on signal distortions. On these lines depends transmission lines stability. Let’s see how transmission lines affect transmitted signals. (G- signal generator; Za– output impedance; I- signal receiver Zb– input impedance; L- transmission line length; Z0– Line impedance. When line is tuned and without losses then input voltage: Ub(t) = ZbE(t-t)/(Za + Zb) E(t)- generators signal amplitude; t- signal delay in line. t =l/v ; l- line lenght; v- signal speed. If the line is not tuned up, then there are distortions in line because of reflections inline: If signal E(t) is step function: Then signal in line exit in discrete time moments will be: U(0) = p; U(t) = p*(1+pb) U(2t) = p*(1+pb+pa*pb) U(3t) = p*(1+pb+pa*pb+pa*pb^2); U(4t) = p*(1+pb+pa*pb+pa*pb^2+pa^2*pb^2); U(5t) = p*(1+pb+pa*pb+pa*pb^2+pa^2*pb^2+pa^2*pb^3) â€¦ where Depending on reflectance coefficients and their signs distortions can differentiate or integrate: A real model using MathCAD was implemented to see how the signal looks on exit depending on parameters. Below you see used algorithm structure used in modeling: Part 2: One of results using trapezoid signal: In exit we get distorted…

## Filter output dependency on tolerance of elements Sometimes we need to project a simple filter with particular characteristics. We usually take calculations with ideal parameters and don’t look at tolerances of them. Let us see how simple filter output depends on its elements tolerances. For this let’s choose simple filter circuit: We are going to calculate the filter response characteristics. The bandpass frequency is taken on 0.707 level of response. We will see how this frequency depends on the electronic element tolerances. I will model elements with tolerances ±10%.

## Z axis accelerometer MMA1220D from Freescale MMA1220D is Z-axis MEMS accelerometer -8g – +8g. This sensor has a capacitive sensor. The output signal is passed through a 4 poles low pass filter. It also has an internal self-test capability. The main features:Integral signal conditioning;Linear output;Ratiometric performance;4th order Bessel Filter to preserve pulse shape integrity;Calibrated self-test;Detection of low voltage also clock monitor and EPROM Parity check status;Can survive big shocks. Where can it be used? It can be the perfect tool for Vibration monitoring, control, bearing monitor, PC HDD protection, mouse and joystick, virtual reality, sports diagnostics.The datasheet can be found here:https://www.freescale.comI decided to run a sample test for this sensor. For this, I just made a simple board where I soldered this sensor with the SOIC16 package. According to the datasheet, I put an RC filter on sensor output to minimize clock noise. There is a schematic: And traced PCB: I used SMD parts as it will be easier to glue another side of the board to any surface in the future. First test drive on oscilloscope: Later I will do some tests by connecting this sensor to MCU.Bellow, I attached the Protel library of the MMA1220D sensor and my project files. It might be you…

## Physiological system modeling Most physical and chemical experiments can be described with a finite number of rules. In physiological processes, everything can be tied to the laws of nature. A good model can be a guideline for new experiments. Usually, the model and experiment have an iterative connection. To understand how to investigate any material, there is a model needed (block 1). First, we need an abstract understanding of what we are investigating (block 2). Abstracts are transformed into mathematical models (block 3). There we can use formulas and solve them using the computer. The results you get shows, what experiments have to be done, and what to expect from them. This loop system is resistive to irregularities in the mathematical model. In other words, this is the purifier of experiments and models.

## CMOS and TTL compliance There was a time when all IC’s were only TTL type. They were marked as 74LS or 74ALS. But then there came CMOS types of semiconductors. They are usually marked CDxx. And lately, there appeared combined semiconductors that are compliant with both types. They usually are marked as 74HC or 74HCT.TTL is faster than CMOS, but they sink more power. They are powered from a 5V source. To diminish the power consumption, the CMOS was developed. They can work with supplied voltages in the range of 3 to 15V. The main disadvantage is that they are static sensitive. So you always have to be grounded when working with CMOS.Now both types of semiconductors are widely used. Sometimes there is a dilemma to connect TTL to CMOS. You cannot connect TTL directly to CMOS as there are different supply voltages. So it would help if you had some compliance circuit. The simplest can be bipolar transistor cascade. Just remember that such a cascade inverts the signal, so you might need to put an inverter in front of CMOS. Another reminder – never leave TTL or CMOS free pins hanging. Jus connect them through a resistor to VCC or GND.

## Polarizer test I used a simple lamp directed to the glossy table surface. One polarizer is in front of the lamp, and the other is in front of a digital camera lens. Both polarizes perpendicularly oriented to each other. How does this work? A theory about an angle on which the incident polarized electromagnetic waves turn reflects from the surface with a polarization plane turned in 90 degrees. When light going through the polarizer towards the surface, the light is polarized in one direction, and when it reflects from the surface, it is turned by 90 degrees. Another perpendicular polarizer filters those waves in front of the lens.