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---+ Switches

There is quite a variety of different types if switches starting from a simple push button to reed switches which are sensitive to magnetic field, mercury switches and the "magic cup" as well as the relay, which allows to control high power signals with a low power signal.
---++ The push button

The simplest switch device is a pushbutton. It short-circuits 2 pins if pushed and opens them when release. The little PCB board contains a 10 k&Omega; resistor, which can be used to pull up one of the 2 leads to a Vcc voltage level and which can be switched to ground by pushing the switch.
| <img alt="pushbutton.png" height="300" src="%ATTACHURL%/pushbutton.png" title="pushbutton.png" width="244" /> | <img alt="pbschematic.png" height="305" src="%ATTACHURL%/pbschematic.png" title="pbschematic.png" width="192" /> |
| The pushbutton | Circuit diagram of<br />pushbutton PCB |
---++ Mercury switches

There are 2 different types of Mercury switches which contain a small mercury ball short-circuiting 2 leads. When the device is tilted the mercury flows away from the leads and the contact opens. Both PCBs contain a Mercury switch and a LED connected in a different way however. There are 2 PCBs with a mercury switch and a big LED which can be operated directly from 3.3V without an additional current limiting resistor. These PCBs are also called "magic cups" because they can be programmed such that you can "pour light" from the LED of one PCB to the other by inclining the board.
| <img alt="newmercury.png" height="248" src="%ATTACHURL%/newmercury.png" title="newmercury.png" width="168" /> | <img alt="mercurySwitchSchematic.png" height="249" src="%ATTACHURL%/mercurySwitchSchematic.png" title="mercurySwitchSchematic.png" width="116" /> |
| Mercury switch | its circuit diagram |

| <img alt="newmagicCup.png" height="249" src="%ATTACHURL%/newmagicCup.png" title="newmagicCup.png" width="200" /> | <img alt="magicCupCircuit.png" height="253" src="%ATTACHURL%/magicCupCircuit.png" title="magicCupCircuit.png" width="155" /> |
| The magic Cup | its circuit diagram |
---++ The Ball Switch

The ball switch works exactly the same way as the mercury switch. The only difference is that the mercury blob is replaced by a metal ball. However, the ball switch PCB does not include an LED but just a 10 k resistor and its diagram corresponds to the one of the pushbutton.

<img alt="ballSwitch.png" height="248" src="%ATTACHURL%/ballSwitch.png" title="ballSwitch.png" width="161" />
---++ Reed Switches

A Reed switch reacts on magnetic fields and creates a short circuit when a strong enough magnetic field is in its neighborhood. The reed switch comes in 2 versions which however have essentially the same functionality. While the first one is mounted on a PCB by itself (again with a 10 k&Omega; resistor that can be used to pull one of the leads up to Vcc) the other one is mounted on a PCB which is normally used for analogue sensors.

| <img alt="miniReed.png" height="202" src="%ATTACHURL%/miniReed.png" title="miniReed.png" width="225" /> | <img alt="bigreed.png" height="287" src="%ATTACHURL%/bigreed.png" title="bigreed.png" width="146" /> |
| simple reed switch | reed switch on analogue board |

A special switch is the relay, which contains 2 independent circuits: The primary, low power circuit which activates a magnetic switch through which a high power secondary circuit gets powered. In our case we can switch a 220 V circuit with a mere 3.3V signal.

To test this circuit we will however only switch a LED on a 5 V circuit with a signal from the primary 3.3V circuit.

<img alt="relay.png" height="285" src="%ATTACHURL%/relay.png" title="relay.png" width="361" />

-- %USERSIG{UliRaich - 2017-01-15}%

---++ Comments

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Attachments

Topic attachments
I	Attachment	History	Action	Size	Date	Who	Comment
png	ballSwitch.png	r2 r1	manage	707.1 K	2017-01-28 - 12:22	UnknownUser	ball switch
png	bigreed.png	r1	manage	588.4 K	2017-01-15 - 19:14	UnknownUser	reed switch on analogue board
png	magicCupCircuit.png	r1	manage	5.0 K	2017-01-28 - 12:43	UnknownUser	schematic of mercury switches
png	mercurySwitchSchematic.png	r1	manage	4.0 K	2017-01-28 - 12:43	UnknownUser	schematic of mercury switches
png	miniReed.png	r1	manage	2054.5 K	2017-01-15 - 19:11	UnknownUser	simple reed switch
png	newmagicCup.png	r1	manage	754.8 K	2017-01-28 - 12:16	UnknownUser	mercury switches
png	newmercury.png	r1	manage	720.1 K	2017-01-28 - 12:16	UnknownUser	mercury switches
png	pbschematic.png	r2 r1	manage	8.5 K	2017-01-28 - 12:03	UnknownUser	pushbutton circuit diagram
png	pushbutton.png	r1	manage	2273.8 K	2017-01-15 - 19:11	UnknownUser	push button
png	relay.png	r1	manage	3347.8 K	2017-02-04 - 13:47	UnknownUser

Topic revision: r3 - 2017-02-04 - uli