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Topic: Car horn causing servos to go crazy (Read 330 times) previous topic - next topic

Jhearnsberger

I built a toy car and have a real car horn and windshield wipers using two sg90 servos.  The car horn is 12v and draws around 12 amps when sounded.

When you sound the horn the servos sporadically jump around just for the period of time you sound the horn.

The servos are on an external power source separate from the horn.  The servos wires and the horn wires going to the switch panel are in the same wire bundle.

jremington

#1
Jun 17, 2019, 05:28 am Last Edit: Jun 17, 2019, 05:30 am by jremington
No surprise there. Try separating the wire bundles.

I imagine that a 144 W horn makes quite an impression on a toy car.

Jhearnsberger

Is there any kind of filter I can put in the line?  The bundle is pretty hard mounted and tied at the moment?  Anything I could try before running separate wires?

jremington

#3
Jun 17, 2019, 05:37 am Last Edit: Jun 17, 2019, 05:45 am by jremington
Without seeing a complete wiring diagram, anyone would just be guessing. You could have capacitive cross coupling, ground loops, magnetic cross coupling, supply drop, high voltage transients, etc.

But in any case, a really basic wiring rule is to keep power conductors separate from signal conductors, and in some cases, you may be required to use electrical shielding between them.

Jhearnsberger

Here is a diagram.  That will be awesome if I can just run separate signal wires down the opposite side.  Are cat5 wires large enough to send a signal over 10ft?

zwieblum

Seperating wires alone won't help, the car horn needs propper decoupling and it produces noticable sparks while making sound.

jremington

#6
Jun 17, 2019, 04:42 pm Last Edit: Jun 17, 2019, 04:44 pm by jremington
According to the wiring diagram, the horn circuit has nothing to do with the Arduino circuit, so just run two new wires to the horn switch, as far as possible from the Arduino circuitry.

The circuit diagram does not show how the Arduino is powered. If it is the same as the 5V servo power supply, that needs decoupling. A 1000 uF capacitor from power to ground, close to the Arduino should help. Do not try to power motors or servos from the 5V output of the Arduino.

MarkT

I built a toy car and have a real car horn and windshield wipers using two sg90 servos.  The car horn is 12v and draws around 12 amps when sounded.

When you sound the horn the servos sporadically jump around just for the period of time you sound the horn.

The servos are on an external power source separate from the horn.  The servos wires and the horn wires going to the switch panel are in the same wire bundle.
Car horns are extremely electrically noisy, substantial filtering would be needed, probably better to use an audio player with some horn samples - and far less painful on the ears.
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