PCM Wk 8: Transistors, Relay, Motors

Notes:

For controlling devices that need more electrical current than micro controllers can supply, we can use 1.) relays, 2.) transistors, 3.) optoisolator
Relays – devices that control a switch through magnetism; a little slower to close ( a few miliseconds delay)
- 2 types of relays: electromechanical, solid states
  - solid state relays: metal contact switch; able to control AC
  - electromechanical: using magnetic field to close the switch
Transistors: used for switching a higher current circuit rapidly; they are electronic devices that can work as a switch; faster than relays
- allows control of larger current by a smaller current
- 3 connections: 1.) base, 2.) collector, 3.) emitter
3 differences between relays & transistors:
- motor as load; motors are inductive loads –> creates a reverse voltage when spinning
- protection diode: in parallel with transistors; protection diodes routs any reverse voltage around the transistor to protect it
- microcontroller : attached to the base/gate. transistor’s emitters and base must have a common ground
Helpful Tip: ” if you are switching DC motors, solenoids, or other high-current DC devices which create motion, it’s better to use a switching transistor than a relay”

Questions:

It says ” One of the main differences between MOSFETS and bipolar transistors is that MOSFETS require negligible current on the base in order to activate.” What does “negligible current” mean?
Need to better understand transistors and how the base, collector, emitter work.
Why are MOSFETS using the term “drain”, “source” instead of “emitter” or “collector” like the bipolar transistors? Why the different names if they are doing the same thing? Are they doing the same thing?
When do I know when I should use a transistor versus a relay switch? Is there a best practice for when to use which?

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Notes:

H-bridge to control a DC motor from a micro controller. H-bridge chip includes diodes to protect the transistor from back voltage
DC Motor’s speed is proportional to the supplied voltage
Best way to adjust speed is by using PWM (~ on the Arduino)

Questions:

Regarding: “The top two transistors above are P-channel, meaning that they allow current to pass when and the bottom two are N-channel, so that the proper two transistors always switch together. When the left control pin is high, transistor 1 (labeled Q1) turns off because it’s a P-channel and Q2 turns on because it’s an N-channel. The same happens with Q3 and Q4. If you were using this circuit, you’d want to make sure that the control pins are always reversed; when one is high, the other is low” , I don’t think I understand this.

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Notes:

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Notes:

stepper motors rotate a full 360 degrees, but unlike dc motors, they can be positioned at a particular angle
stepper motor: a motor controlled by a series of electromagnetic coils; center shaft has a series of magnets mounted on it
- coils surrounding the shaft are alternatively given current or not–> this creates magnetic fields which repulse or attract magnets on a shaft
2 types of stepper motors:
1. unipolar stepper motors:
  1. 5/6 wires
  2. 4 wires = 4 coils connected by 1 pole
2. bipolar stepper motors:
  1. 6 wire motors: 2 coils divided by center connections on each coil
  2. 4 wires coming out of it
Stepper motors receive more power than micro controllers can give them (like other motors)
H-Bridge Control of Stepper Motors:
- apply voltage to each coils in a specific sequence in order to control the stepper
Both uni and bipolar motors can be controlled with an H-bridge
to know the position, just need to count how many steps and how many degrees (Ex: 1.8 degrees stepper X 200 steps = 360 degrees)
2 wire controls: 2 wires are always set to opposite polarities

Questions: