A (probably) simple RC circuit question

In summary, the person is looking for advice on how to build a circuit to control a solenoid which will turn on and off a light bulb. They have looked into programmable controllers but find them to be overkill. A 555 and two BJTs will do the job. The solenoid can be turned on and off at a frequency of 3-15hz and the ramp time can also be adjusted.
  • #1
oldguy
3
0
Its been 30 years since my last Physics course so while I have the basic concepts I'm uncertain how to solve my current problem: I need to operate a pair of 12V solenoids (.5 seated amps, 4 watts each) with a periodic on/off cycle that gently ramps to full voltage (over about .5 to 1 sec) and then shuts off, repeating every 5-10 seconds (I'd love to be able to adjust this once my device is built and tested). It sounds like an RC circuit to me in theory but I'm lost as to how to proceed in reality at these voltage/amperage levels. I've looked into programmable controllers but this seems like over-kill for what strikes me as an essentially simple operation.

I'd love any help or thoughts on where to go to educte myself on this topic.

Thanks.
 
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  • #2
one 555 and a two bjts will do what you want, use one after the 555 (5-10 second adjustable pulse) with a drain resistor and cap that determines the rc time ramp of the base of the second bjt.
 
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  • #3
what is ".5 seated amps"
 
  • #4
light_bulb: Thanks so much for the prompt response--it sounds like its very do-able but I'm strictly an amateur as far as real-world applications--would you mind taking a minute and breaking it down for me (or point me at a resource for understanding your response). don't know 555 or bjts and how do I figure out where to start to estimate values for resistor and capcitor. (sorry). thanks again.

and to moe_3_moe: seated amps refers to the steady state draw when the solenoid is fully activated and in the held state--
 
  • #5
i made the circuit, should be adjustable from 3-15hz, and the ramp time also. didn't test it but i figure it's good for illustration. it is an astable circuit off the data sheet with a series resistor-cap off the discharge leg that is adjustable to turn the square wave into a slight saw. once again didn't test.
 

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  • #6
wow. thanks very much-that's phenomenally helpful. I'll dig in and see if I can put this together. I really appreciate your time.
 

1. What is a simple RC circuit?

A simple RC circuit is a circuit that consists of a resistor (R) and a capacitor (C) connected in series. It is a basic electronic circuit that is used to control the flow of electrical current.

2. How does a simple RC circuit work?

In a simple RC circuit, the resistor limits the flow of current while the capacitor stores electrical charge. When the circuit is turned on, the capacitor begins to charge up to the same voltage as the power source. As the capacitor charges, the voltage across the resistor decreases, and the current flowing through the circuit also decreases. Once the capacitor is fully charged, no more current flows through the circuit.

3. What is the time constant of an RC circuit?

The time constant of an RC circuit is the time it takes for the capacitor to charge up to approximately 63% of the power supply voltage. It is calculated by multiplying the resistance (R) in ohms by the capacitance (C) in farads, T = RC.

4. How does the value of the resistor and capacitor affect the behavior of a simple RC circuit?

The value of the resistor and capacitor in a simple RC circuit determines the time constant and the time it takes for the capacitor to charge up. A higher resistance or capacitance value will result in a longer time constant and a slower charging rate. The capacitance also affects the amount of charge the capacitor can store, while the resistance affects the amount of current that can flow through the circuit.

5. What are some practical applications of simple RC circuits?

Simple RC circuits are commonly used in electronic devices such as filters, timers, oscillators, and voltage regulators. They are also used in power supplies, audio circuits, and radio frequency circuits. Additionally, RC circuits are used in biological systems, such as nerve cells, to model the charging and discharging of electric potentials.

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