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[on:]

I have a load activated by a button. I need it to gradually draw voltage and current as if it is being activated by a slider or knob. What simple, cheap device will do that for me up to 12v 3.5amps?

[Reply #1 on:]

Look for a feature called "soft start", you fin it on a lot of power regulators and switches.

[Reply #2 on:]

I have a load activated by a button. I need it to gradually draw voltage and current as if it is being activated by a slider or knob. What simple, cheap device will do that for me up to 12v 3.5amps?

That's a request I haven't seen before. Perhaps if you wired a digital output pin to a fairly large R/C network that then wires to the gate of a N channel power mosfet, it would turn on (sink to ground) rather gradually causing that slow turn on you require.

Lefty

[Reply #3 on:]

Look for a feature called "soft start", you fin it on a lot of power regulators and switches.

I'm trying but can't find anything that fits the bill

[Reply #4 on:]

What exactly is your goal? There may be a more clever way of accomplishing it if there was more information.

[Reply #5 on:]

Put a serial inductor there.

[Reply #6 on:]

Put a serial inductor there.

have a link? I can't find much..

[Reply #7 on:]

Can the load be PWM'd ?  What is the load?

[Reply #8 on:]

What sort of load is it? Perhaps you could use PWM to power it and gradually ramp the duty cycle up from 0% to 100%.

[Reply #9 on:]

Can the load be PWM'd ?  What is the load?

Suspected issue:

http://arduino.cc/forum/index.php/topic,140951.0.html

[Reply #10 on:]

I've seen it done like this before. First your load receives power through a 1 ohm resistor (fiddle with the value) and the capacitor slowly charges up to the relay turn on voltage. Once the relay latches, it and your load receive full power since the resistor is bypassed. Make sure you use a high wattage resistor.

[Reply #11 on:]

Possibly a MOSFET could be controlled with increasing PWM to gradually increased the total current being supplied.

[Reply #12 on:]

OP - you need to put some time measurement into that first graph, the solution depends on how long you want the ramp to take.

You also need to say if the current is AC or DC.

[Reply #13 on:]

500ms from no load to full load. DC.

[Reply #14 on:]

According to my son-in-law's father "you move the switch slowly"   
So much for his knowledge of electrickery