/sci/ - Science & Math

[Anonymous No.5776123]

I'm trying to make sense of this circuit that tells a motor to switch directions when certain pressure buttons are pressed, but I'm having some problems understanding why certain elements are there. I've marked them for clarity.

The upper part of the network (pin 4+5) is supposed to be a system that works as follows:
It drives a motor that can switch direction of rotation by means of a relais. Pin 5 does this. If a 1 signal (3.3V) comes from pin 5, a voltage difference is created over the coil and the motor changes directions (the switch closes). If pin 5 outputs a 0 signal the 12V will let straight into the ground. Pin 4 is just there for putting the motor on and off; if it outputs a 1 signal (3.3V) the motor will rotate, if it outputs nothing it won't.

The lower part of the network (pin2+3) is meant to interpret the signals of the pressure buttons. When one of the buttons is pressed, this information should be send to the microcontroller (the pins) so that a written program can then make the motor stop rotating, switch rotational direction and start rotating again. Supposedly the microcontroller also has a quasi infinite resistance for some reason, which I'm very much confused by.

Is there anyone here who understands the functions of the marked elements or can in other ways help to interpret this circuit. Any help would be very much appreciated.

[Anonymous No.5776159]

No EE's or other technology enthusiasts?

[Anonymous No.5776168]

>>5776123
The red thing connected to the yellow thing
The yellow thing connected to the black thing
The black thing connected to the black thing
And they're all surrounded by the white thing.
---->my racial commentary

[Anonymous No.5776181]

>>5776168
Well.. thanks for your input? I guess..

[Anonymous No.5776235]

bump

[Anonymous No.5776246]

The purple thingies: They are known as "Pull-Down resistors". They set the input to GND when the switch is off and to Vcc when the switch is on. In that case, we have a second resistor that makes a voltage divider, so, the input is set at a lower voltage than Vcc. Note that this thing just works because the resistance of the input pins are extremely high, so, the current it sucks is very low. They are made this way so we can switch the states with a very low current.

[Anonymous No.5776264]

The upper green thingie: It's the motor. This is how a motor looks like electrically (it's a oversimplified model, of course).
The green thingie inside the rectangle: It's the relay coil. It's inside the relay and when current goes through that coil, the relay turns on! Magic!

[Anonymous No.5776278]

>>5776246
I was following until "Note that (..)". Could you elaborate a bit more on that please. I understand that the pins having a high resistance would make the current flowing through them smaller. I don't understand how this explains the resistances in the circuit (or do you mean these by "the pins' resistance"? Plus, doesn't this make R4/R obsolete as -as far as I can see- a voltage divider between the pin and the ground is pretty pointless?

[Anonymous No.5776279]

Finally, the red thingie: When the relay is off, current goes from right to left through the motor. But, notice that when the relay turns on, this connection is inverted and current flows from left to right. And... TADAH! The motor goes in the opposite direction. This is what the red thing does: Invert the connection to the motor when the relay turns on.

[Anonymous No.5776298]

>>5776264
Will the relay coil close both relais?

[Anonymous No.5776314]

>>5776278
Well... let me explain clearly.
When the switch is off, Vcc don't reach our circuit. Then, R3 is floating, so, it don't exist. The current that goes through R4 is extremely low (lets say it's 0), so, the voltage in the resistor R4 is also 0. It means our pin 3 voltage is... guess what? 0.
But when the switch is on, we have now the 12V source and R3 on our circuit. It makes a tension divider with R4 and drives our pin R3 with the voltage on R4 (around 3V, I think).

>>5776298
Yeah. Will close both the contacts. The rectangle represents a single relay on the rectangle.

[Anonymous No.5776352]

>>5776314
Oooh, it's basically just dropping of an excess of voltage so it can deliver 3.3V to the pin. That totally makes sense. Thanks man. I'm not even sure if there's anything left in this circuit that I don't understand now.

But seeing that I have you here now and you're clearly awesome (no really, thanks): I was having a bit of an issue grasping these MOSFETS theoretically. I'm confused about what makes them close and open and how voltage comes into this all.

[neckbeard_the_pirate No.5776376]

>>5776123
>The relay only reverses the current when energized.
>M1 selects forward or reverse on the relay.
>M2 is used to actually supply power to the motor (on/off)
>the purple resistors are used to interface the 12V switch signal into a 3V signal.
Also, the voltage regulator has the input/output wired backwards.
/DIY/ might be able to handle this better.

[Anonymous No.5776385]

>/sci/
>learning a little bit, every day.

[SciDropout No.5777606]

For one thing, you show the output of a 5 volt regulator IC connected to "12V voeding." If you connect the output of a 7805 to 12V, it will blow up or burn out if the input to the regulator is not at or above 12V. It over biases the output transistor array in that IC. Another thing is that switching the relay will do nothing but make sparks and interrupt the circuit for the time it takes to switch. In other words, this looks like a botched design.

[Anonymous No.5777679]

>botched design

fix'd

[SciDropout No.5777697]

>>5777679
Good job!