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Generated millions of times every day by our telephone keypads, the eight DTMF frequencies were chosen so that the harmonics and intermodulation do not generate significant in-band signal levels. The signal is encoded as a pair of sine waves, ensuring that no frequency is a multiple of the other and the sum and difference between two frequencies does not match any single tone and that’s why DTMF sounds so ugly!T he DTMF encoder circuit show n here is based on the HT9200B tone generator device produced by Holtek and distributed by Futurlec among others. The encoder is complemented by a decoder elsew her e in this publication. 8-Channel DTMF : Encoder Schematic The HT2900B is supplied as a nice old fashioned 14-pin device. It can be instructed by a microcontroller to generate 16 dual tones and (in serial mode only) 8 single tones from the DTMF pin output . It s 8 - pin ‘ younger brother’ the HT9200A provides a serial mode only whereas the HT9200B contains a select-able serial/parall...

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On line Ladder Program Editing for RSLogix 500

April 02, 2017

On line Ladder Program Editing for RSLogix 500 There are five basic steps in performing an edit on line. 1) Start Edits, 2) Make Changes, 3) Accept edits, 4) Test Edits, and 5) Assemble edits. Although these steps seem very simple there are a few rules to watch out for. You cannot expand or create a data table on line in the SLC, and you must be in program mode (or off line) to expand a data table on line in the PLC-5. You cannot make an on line edit if the key switch is in Run Mode. In the PLC-5, if backplane switch 8 is on, you cannot make an on line edit. You do not need to perform an on line edit to directly change a value in the data table such as the preset of a timer or counter. If the processor is in program mode, you do not need to test and assemble after accepting. If the processor is in program mode, and a rung is deleted, there is no warning. Let's walk through the 5 step procedure: L...

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Metal Detector Based on the TDA0161

March 18, 2017

These metal detector circuit diagram is based on the TDA0161 monolithic integrated circuit , designed for metallic body detection by detecting the variations in high frequency Eddy current losses. For detecting metals , TDA0161 require an external LC tuned circuit . Metal Detector Circuit diagram Output signal is determined by supply current changes. Independent of supply voltage, this current is high or low according to the presence or the absence of a close metallic object. This metal detector circuit use two LEDs , which offer an visual indication of presence or absence at a metals ,around the coil . To adjust the circuit you need to make sure there is no metal near the coil and then set the fine adjustment to a "Mid position". After that you need to adjust the course adjustment to turn on the LED and , adjust the fine adjustment to turn off the LED. This detector electronic circuit operates over a wide range input voltage of 4 -35 volts . If you want you can use other va...

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