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5 Second Ramp Generator for Locomotive Sound Card Demonstrat

2017-01-17 01:14  
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5 Second Ramp Generator for Locomotive Sound Card Demonstration
The circuit on this page is designed to produce a timed throttle output for demonstrating on board sound systems in a large scale locomotive. When a push button is activated the output will rise from 0 to 15 volts in 5 seconds. The voltage will then hold for 5 seconds. The voltage will then return to 0 in about 10 seconds. When S1 is pushed the 555 timer will start and run for 10 seconds. For the first 5 seconds the 10 uF capacitor at the PLUS input of the LM 358 or LM324 OPAMP will charge until it reaches the voltage at pin 5 of the 555 timer chip plus 0.7 volts The voltage across the capacitor will now be steady for 5 seconds. When the timer shuts off the voltage across the capacitor will decay to 0 over a period of 10 seconds, 5 seconds if the optional diode and resistor are used. The output of the OPAMP drives a conventional transistor throttle output section. Notes The 500K ohm variable resistors are used to adjust the charging rate so that the capacitor at the PLUS input of the OPAMP reaches it maximum voltage (2/3 of the supply - plus 0.7 volts) in 1/2 of the timers output duration. This control could be replaced by a fixed resistor once the required value is determined. The circuit is designed to produce an output of15 Volts when operated from a well filtered or regulated 20 Volt power supply only. If voltage adjustment is required the value of the 13K ohm resistor can be increased to give a lower output voltage or it can be decreased to give a higher output voltage. This circuit has no automatic current limiting or overload protection. With a proper supply the circuit will deliver about 2 amps. A heat sink may be needed for the output transistor. The parts values shown on the schematic drawing are calculated to give the desired times and output voltages. Due to value tolerances of all of the parts and the leakage currents of the capacitors some adjustment may be required to achieve the desired results.