Filter output dependency on tolerance of elements

Sometimes we need to project simple filter with particular characteristics. We usually take calculations with ideal parameters and don’t look on 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 filter response characteristics. The band pass frequency is taken on 0.707 level of response. We will see how this frequency depends on electronic elements tolerances. I will model elements with tolerances ±10%.

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Z axis accelerometer MMA1220D from Freescale

MMA1220D is Z axis MEMS accelerometer -8g – +8g. This sensor has capacitive sensor. The output signal is passed through 4 pole low pass filter. It also has internal self test capability. The main features: Integral signal conditioning; Linear output; Ratio metric 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 high shocks. Where it can be used? It can be perfect tool for Vibration monitoring, control, bearing monitor, PC HDD protection, mouse and joystick, virtual reality, sport diagnostics. The datasheet can be found here: http://www.freescale.com I decided to run sample test of this sensor. For this I just made simple board where I soldered this sensor with SOIC16 package. According to datasheet I put RC filter on sensor output to minimize clock noise. There is schematic: And traced PCB: I used…

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Emergency supply source for your electronic device

Sometimes you are needed to maintain power supply for your device for some time when the main source fails. It can be alarm system or some light source or digital clock. Of course if source interrupts are very short, there can be capacitor with big capacity connected, but it is not reliable. Better use backup battery and diode. This solution is very simple and cheap. The diode protects the back current float to battery. This doesn’t take much space to implement as the main bigger part is battery. As there just backup source it is not necessary to use rechargeable battery.

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Physiological system modeling

Most of physical and chemical experiments can be described with a finite number of rules. In physiological processes everything can be tied to laws of nature. Good model can be as a guideline to new experiments. Usually model and experiment has iterative connection. In order to understand ho to investigate any material there is model needed (block 1). First we need abstract understanding about what we are investigating (block 2). Abstracts are transformed into mathematical model (block 3). There we can use formulas and solve them using 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 mathematical model. In other words, this is the purifier of experiments and models. How to model blood vessels There can be many modeling ways of them. This is because, that every model has its own benefits and…

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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 semiconductor. They are usually marked CDxx. And lately there appeared combined semiconductors who are compliant to both types. They usually are marked as 74HC or 74HCT. TTL are faster than CMOS, but they sink more power. They are powered from 5V source. To diminish the power consumption, the CMOS were developed. They can work with supplied voltages in range 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 as dilemma to connect TTL to CMOS. You cannot connect directly TTL to CMOS as there are different supply voltages. So you need some compliance circuit. The simplest can be bipolar transistor…

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Polarizer test

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

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