SparkFun Forums

[grantkaye]

Hi there, looking for answer to a basic electronics question from my perspective of not really knowing that much on the subject. I am wondering if it is possible to design a circuit that operates two sub-circuits of different voltages, so they can interact. If I already put my foot in my mouth and lost you let me try to explain a bit more clearly.

I have one circuit that consists of a 3.3V signal that is sent by a PCB-based timer in regular intervals from a battery to a servo. This operates one servo which is on when the voltage is sent, and off when there is no voltage present. An example application is to have the servo on for 10s, then off for 2, then on for 10, etc. until otherwise directed by the user.

The other circuit consists of a 12V gear motor that moves the servo around. Right now the motor is either on, or off - meaning that the servo is moving while it is on. What I want to do is to create an overall circuit design that would "read" that the 3.3V circuit is actively sending voltage to the servo, and interrupt the 12V circuit. So in other words, the motor would cease to move the apparatus while the 3.3V circuit was live. I want the 12v circuit to die when the 3.3V circuit is active.

No I'm a dummy when it comes to these things. Would I use a mechanical relay that opens a normally closed switch in the 12V circuit?

I know I can do this via Arduino but I want to see if there is a simpler hardware solution. If anyone has any ideas, I would love some feedback and references to what I would need to buy on Sparkfun to build it.

Thanks!

[esklar81]

grantkaye,

How are you turning the 12V motor on and off? How much current does it draw?

You are on the right track about using the 3.3V signal to open a relay that feeds the motor. The details, such as what components you'll need, depend on what you already have and how much current the motor draws.

3.3 V is rather low to drive a relay directly, but you should be able to find an optoisolator that will work on that voltage. Unless your motor is very small, you will need to use the optoisolator to control a relay and the relay to control the motor.

Have Fun,
Eric

[grantkaye]

Eric - thanks so much for your reply. Right now the 12v motor speed is controller by a pulse-width modulated PCB (http://www.sparkfun.com/products/9668 - but I bought the 5A version because the motor only draws a few amps). It is on/off via a simple toggle switch. So the motor is on, and the PWM speed controller dictates the speed.

I'll look into what you suggested, thanks again!