This design will interest technicians who work on pneumatically operated valves and other 4-20mA current loop controlled devices. Although 4-20mA signal injector/calibrators are available, this one is both cheap to build and easy to operate. When first powered up, the circuit sinks 4mA of current. If switch S1 is pressed, the current level slowly
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ramps up to 20mA, pauses and then ramps back to 4mA. This cycle will continue unless the switch is pressed again, whereby the output will lock to its current level. A further push of the switch resumes the prior cyclic operation. Output2 from the micro (IC1) is programmed to generate a pulse-width modulated (PWM) signal to drive the current sink transistor (Q1). The digital PWM signal is converted to an analog voltage using a low-pass filter formed by the 1k ‰ series resistor and a 4. 7 F tantalum capacitor. By varying the PWM duty cycle and therefore the DC signal level out of the filter, the program can indirectly vary the current flow through the transistor. A 100 resistor in series with the emitter of Q1 converts the loop current to a small voltage, which is fed into the micro on input1. The program uses this feedback signal to zero in on the desired current level with the aid of the micro`s analog-to-digital converter. Details of this can be seen in the accompanying program listing. If the PICAXE senses an open circuit, it shuts down the output and goes into an alarm state, to alert the operator and protect the circuit under test. The switch can be pressed to reset operations to the start once the open circuit has been rectified. The LED flashes a code for various milestones, as follows: one flash at 4m and one flash to confirm a switch press two flashes at 12m when ramping up (for the first 5 cycles); three flashes at...
This project fits more for custom made battery casing that can have more space to hide things inside. This switch with few alterations can be used for any other project as well but is designed based on e-bike needs! This project use a clever functionality of....
The circuit described here uses ultrasonic oscillations and operates based on the propagation velocity of these oscillations in the air. Thus, we can easily determine the distance of two points if the time within which the wave travels this distance is....
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This Amplifier was designed to have the following specifications: Distortion less than 0.1% at full power of 100W even at 20KHz. Power has to be attributed to an extended bandwidth. The output transistors must be protected against short circuits. The power....
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