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I have previously written quite a few articles on sinusoidal pulse width modulation (SPWM). I've discussed about how to generate the sine table, how to implement it, how to practically generate the SPWM signals (with example code) and also how to implement feedback with simple sine table manipulation with table pointer instead of complex PID control. All these methods have one thing in common regarding the implementation - use of the sine table and its control with the table pointer. Whether you use or implement feedback or not, the table pointer is used to access and retrieve values from the sine table. Before reading or going through this article, I suggest you go through these first: Tutorial (Click here to open tutorial): Generation and Implementation of Sine Wave Table   Article (Click here to open article): Smart Sine – Software to generate sine table Article (Click here to open article): Generation of sine wave using SPWM in PIC16F684 It took quite a while for me to unde...

A temperature sensor and a hot transistor hold biological samples at a preset temperature. It is common to use transistors for driving resistive heating elements. However, you can use the heat that a power transistor dissipates to advantage in several situations, eliminating the need for a separate heating element because most transistors can safely operate at temperatures as high as 100°C. A typical example is in a biological laboratory, in which the need for maintaining the temperature of samples in microliter-sized cuvettes is a common requirement. The space/geometry constraint and the less-than-100°C upper-temperature limit are the basic factors of the idea. Electronic Circuit Project Use a Transistor as a Heater: Figure 1. IC1 senses the temperature of the item that Q2 heats, and the temperature remains at the level that VR1 sets. You can use an N-channel IRF540 MOSFET to directly heat and control the temperature of a biological sample from ambient to 45°C. Figure 1 shows a simple...

Use of diodes as surge suppressors Contactors are generally designed in such a way that a slight contact welding during closing is forced open again by the back pressure springs of the contacts during de-energization. Diodes can reduce the drop-out speed of a magnet system to such an extend, that the abovementioned slight contact welding cannot not be opened anymore In the extreme case the low drop-out speed caused by the diode can lead to a so-called two-step drop-out. This means that following the first contact opening, another short, weak closing of the main contacts may happen during the breaking process. This second closing (during the arcing time) can lead to welded contacts. Since two-step drop-out cannot happen with size S00 3RT1 contactors, diodes as surge suppressors are offered for this size only. From size S0 upwards diode assemblies (series connection of diode and zener diode), RC-elements or varistor have to be used as surge suppressors. Some companies on the market o...