Working with 555 timer and oscilloscopes

The 555 Timer is different from other microcontrollers in which it fires electric pulses in order to keep track of time.  The way it works is that a capacitor is filled by a resistor and then emptied out by a different resistor.  Depending on your arrangement, you can increase the frequency of the pulses by changing one of the resistors for a pot or replacing the capacitor with a different quantity.





An Oscilloscope is a tool used to see the signals at different points of the circuit.  When seeing the grid, it will tell whether the ciruits are correct.  On the screen a V/t graph is drawn so it shows voltage vs. time.



There are three modes in which the oscilloscope works: channel 1,2, and dual mode. Channels 1 and 2 can be setup independently and "dual" allows for side by side comparison of signals.  Normally you dont get what you see in the picture bellow, so you have to do a little work to see the signal pattern.







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10K pot (blue), piezo (round sound emitter)





Toy Hacking

In programing the toy,  I first built a circuit suitable for a LDR and a motor port controlled by the LDR.  The system had a Darlington system so it could supply enough power through out the whole circuit.  The motor with the LDR work in a way that as light befalls the toy it remains motionless and when the child gets close enough, the toy moves its mouth. 


























In the programming....
main:
         readadc 4,b0
         ;debug
         if b0>120 then top
         if b0<70 then bot
         low 1
         low 2
goto main
top:
         high 1
         low 2
goto main
bot:
        high 2
        low 1

......I created a loop system where if the LDR reads above 120 the toy is motionless and if it drops below 70 the toy's mouth moves.  I did it this way so the child can react to the toy when face to face.

Darlington

 In the next setup, we created a Darlington circuit.  A Darlington circuit is a way to increase the gain of the system, what it does is simply the resultant product of the gain of each transistor.  It is used when there is just not enough "brightness" in the ciruit, (i.e. tree light experiment).

Once finished with the Darlington, the light bulb was replaced with a motorized toy.  The toy moved in cojunction with the previous program and if I reversed the hot and ground, the toy moved in reverse motion.

Microcontrollers

 Microcontrollers are mini computer chips that can store

programs in its memory unit, contain processing units,

and create an input/output circuitry all in one unit.

Once a circuit is built, the chip can be program with

a variety of functions such as motor-control, firing of

speakers, processing commands. 

After creating a circuit for the microcontroller, we needed a digital input sensor so we can execute the program for a simple task.  We used a limiting switch so that when we press the switch the LED would light up.

Instead of a switches, analogue sensors can be used.  A LDR (light dependent resistor) is a device in which touch is not necessary to activate a program.  The LDR has variable value (0 to 255) that can be adjusted to perform a task; if values are created in a range above a set point, the task is performed and if it falls bellow the set point then another task is performed.  An example is if one then light flashes, if two then light is off.

Transistor, and logic probe

Transistors work just like relay switches, it has three sections: the collector which recieves the current, the base which controls the current, and the emitter which sends it out. 

 When you combine the transistor with a switch, it is possible to switch the flow of the current.  With the setup to the right we can create a logic probe.

 A logic probe works to help the user find faults in the electronic design. Not only does it do fault finding but it helps in understanding how the electronics work in a system.

Normally the LED is dim when you make the probe touch a "hot flow" the LED brightens up,and when you touch ground the light shuts off; this results in a proper current flow.

 

Continuing wth the breadboard

There are two switches we looked at; slide switches and push buttons.

Slide switches are what the name implies, a sliding mechanism that allows current to flow from one circuit to another.  Each circuit must flow from positive to ground for the system to work.

Push buttons work by pushing the switch to make contact with the circuit.  The two forms are: "normally closed"- the current flows until you push the switch, "normally open" - the current flows when you push the switch. 

 

  Relays have coiled springs inside to switch contacts between ciruits when you push the switch.

Can be imagined to be like car blinkers.

Using the bread board: multimeter, LED's, resistors

First topic was using a multimeter.  This is a device used to check continuity, resistance, voltage, and other functions.  We tested our soldering joints on the PCB board for continuity on two points.  With the multimeter, we looked at voltage.  Voltage comes in to forms: AC or DC, and is directional.  AC or alternating current is what comes out of a wall socket and DC or direct current is something like a battery.

Voltage will run through a LED light and brighten it.  The more voltage, the brighter it gets; too bright and the bulb will burn out.  For parts, next to the current a form of controlling voltage is needed-resistors.

Next is understanding resistors; these components limit how much current can flow through.  They are color coded to provide a value of how much current it takes in. 

The bread board is a great way to test the components.  Each LED has a limit to how much current it can take, so our job is to find out a proper resistor for optimal performance of the system.

First we need to know the "Voltage loop" law or KVL.  This means for any loop circuit voltage must balance: amount generated= amount used. So for a 5V battery with forward loop of 2.5V, the resistor voltage must equal 2.5V.  Thats just the voltage through the resistor.  To find the right resistor we need another law, Ohm's law.  This shows how resistors work...

Voltage across resistor(V) = current through resistor(amperes)*the resistance of the resistor(ohms).  V=I*R

We have voltage and the current is given to us, then we can find the resistor.

2.5V= .02A*R  R=125ohm.

Unfortunately you wont get an exact resistor so find one closest to it.  Also the bigger the resistors value the less current goes through which means a dimmer light and the vise-versa is also true.

Intro to soldering

At the beginning of class we looked at crucial safety rules to prevent any accidents.  We were instructed on how to properly create an acceptable solder joint.

The first assignment was to solder capacitors to a protoboard, then

rewire an AC power unit. 

 Tomorrow we will test our projects with a voltameter for perfect connections.