# Magnetic Pendulum ( With Hall Effect Sensor )

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## Introduction: Magnetic Pendulum ( With Hall Effect Sensor )

Build this simple Magnetic Pendulum with very few components. Hall effect sensor is used to detect the presence of magnetic field, and "push" the pendulum in the exact moment. Electromagnet is "ON" during only 20mS and battery power drain is low.

## Step 5: Circuit & Main Components

Hall sensor: UGN-3503-U

IC1: LM358N( dual OP amp )

IC2: CD4001(quad cmos nor gate )

FET1: IRFD-120( n-channel power mosfet )

## Step 7: Direction Detector

IC1 output will be low when pendulum is approaching it. It will be high when it is moving away.

## Step 8: Monostable

when IC1 out is high, monostable IC2 will trigger with a 20mS output pulse.

## Step 9: Driving FET

pulse from IC2 biases mosfet gate and electromagnet L1 conducts pushing pendulum. It also drives LED on.

## Step 10: Voltage Drop

diode D1 drops 6V from battery to around 5.3v ( optimum voltage ) . Hall sensor will break down above 6v.

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## 4 Discussions

First, thanks very much for taking the time and the effort to post so many great ideas and projects. But, in the interest of learning something, I have a couple of questions about the magnetic pendulum.
1. Why doesn't the magnetic pulse from the coil turn the hall effect device on/off and continue to pulse it every 20 mS, even when the pendulum is not affecting the circuit ? Or is it that this is happening, but the pulses are small enough that the input to NOR gate A never sees a voltage high enough to regard it as a "logic 1"?
2. With C4 connected directly to the battery, it seems to me that it really doesn't do anything in the circuit, since the coil's current pulse would be provided directly from the battery. If the positive side of the coil and C4 were separated from the rest of the circuit and supplied current from the battery through a resistor (about 60 ohms?) I could see the purpose of C4 being there. In that case, the current provided to the coil would be limited to that stored in C4, and it would be easier on the batteries since current flow from the batteries would be limited to about 100mA vice the relatively high current pulses that the coil demands, which would shorten battery life. Thanks in advance, if you can find time to answer this.

Ordered all parts based on schematic , it is not clear as to the the components (A) (B) and thr diode near r5 the 1k resistor ? Do you have a picture of the actual wiring and ( all component values ?

Cool project. Thanks for including a real schematic, it makes it a lot easier to figure out what is going on.