Circuit Hints & Tutorials

[papa]

            Circuit Hints & Tutorials

In this thread, I aim to collect various hints & tutorials related generally to circuits & their parts, for example:
            (Topics below have links to the relevant posts.)

Schematics

Electronic Parts like Resistors, LEDs ...

Soldering for Beginners, including tools

[papa]

            Circuit Hints & Tutorials

Reserved for links to other circuit-related topics

[papa]

In his Newbie ... thread, lhw455 asked some good questions about the schematic & the quality of some parts for assembling the Gateway.  My following responses could apply to more than the Gateway.

    Some things about schematics that I had to learn: a) Some things in a schematic may not mean anything, but may result from how the drawing was created. To my knowledge, the "dots" on the lines in CompuTourist's Gateway schematic (which I edited) do not mean anything.  << Not correct.  See below.  b) Schematics try to represent a circuit's electrical connections in the simplest way possible, not necessarily components' physical locations or the only way to achieve those connections.

What's important about the lines in the schematic & the labels at each end & along the way is they tell WHAT connections must be made, but not necessarily HOW (We work out the best way with the components we have). In a simplistic way, the Gateway schematic says the RFM69 transceiver's GND solder hole & one end on each of both LEDs need a connection to the Arduino compatible's GND. Fortunately, the Gateway's Arduino & the Ethernet Shield plugged into its top have THREE GND sockets AND the RFM69HC transceiver has a GND solder hole on each side. For positioning sake, I solder a wire to the GND hole on the RFM69 side that also has MISO, MOSI, etc that plug into the Arduino / Shield's digital sockets. Then after I strip the GND wire's other end, I can plug it in the Shield's GND socket next to the D13 socket. Two more GND sockets are next to the 5v socket on the Ethernet Shield's analog side. Each of those two Arduino GND socket can receive one lead of a LED & resistor soldered together.

There are other ways to connect multiple components to the same Arduino connection (For example, see here & see here where I talk about making a 3.3 volt friendly prototype shield to be plugged into the top of an Arduino compatible. There I create a junction for multiple components using a section of break away female sockets soldered to a shield's solder strip.) This is not needed for the Gateway since the Arduino & Ethernet Shield have all sockets needed for 3 GND connections.

A good rule of thumb: Responsible circuit descriptions say when a component "quality" is important, like how for this project one must use Arduino compatibles that are (or switch to) primarily 3.3 volt operation.  Otherwise it should be safe to use adequate parts available at a good price. If one can, it's also good to ask.

      << P.S. Another (confusing ?) thing about schematics is the GND label & the GND symbol. In this case, GND (ground) does not mean connected to a stake in the ground. It means connect to a GND connection in the circuit supplying the power, in this case a GND socket on the Arduino. An Arduino's 3v (or 5v) or digital outputs "send" power & then connections to Arduino GNDs complete the circuit's circle for the current to flow as desired.

Here's a good guide for reading schematics, including symbols for electronic parts.

[papa]

        Comments about Common Electronic Parts in Circuits

A good rule of thumb: Responsible circuit descriptions say when a component "quality" is important, like how for this project one must use Arduino compatibles that are (or switch to) primarily 3.3 volt operation. Otherwise it should be safe to use adequate parts available at a good price. If one can, it's also good to ask.

Some of our circuits need LEDs.  The Gateway needs 2 LEDs. I prefer having 2 colors (I picked yellow & green). What quality?  I suggest buy cheap & enough to have for other projects.

You need some low level resistors to protect the LEDs & their Arduino digital pins, like 100 ohm, 220 ohm, or 1 kilo ohms. I prefer 100ohm which lets the LED be somewhat brighter without burning out. For somewhat dimmer LED & to reserve more current to other node parts, use higher than 100 ohms. Resistor tolerance should not matter. Buy cheap & enough to go with other LEDs in the future.

      More about resistors & their purposes in circuits?

To some degree, especially above absolute zero temperatures, everything is both a conductor of & a resistor (or limiter) to electrical current flow.  We're talking about a part intended to be a circuit's rated resistor, with a known ability to limit current flow.

A resistor's ohm rating indicates how much it limits the current it conducts. How do we know the ohm rating?  From the vendor's package, reading the colored ring codes, or (better) use a digital multimeter (DM), a very helpful tool for making circuits.  This tool has two cords. Plug one cord into the DM's COM port & the other into the mAVohm port.  Turn the DM's selector dial to an ohm rating somewhat higher than the resistor's supposed size.  The two cords' other ends are for touching electrical components to get a reading.  Put one cord end on each wire lead of the resistor & (to be most accurate) avoid touching with fingers.  The screen reading should be close to a  standard resistor size: like 100ohm, 220ohm, 1 kilo (thousand) ohm, 10 mega (million) ohm, but rarely exactly.  Close is usually good enough.

Read schematics carefully for resistor sizes.  Don't miss "K" (for kilo or 1,000 times the number value).  Don't miss "M" (for a million times the number value).  Thus, 100 K ohm means 100,000 ohms, one hundred THOUSAND ohms.  Some schematics, instead of ohms, use the Greek letter omega >>   

     
Schematics specify a resistor's ohm size.  Often other sizes will work, but maybe not as well.  Connecting resistors in series (one after another) creates one resistor unit that sums all their ratings, i.e. two 100 ohm resistors in series makes 200 ohms. This is one way to create what we need from available parts. Connecting two equal resistors in parallel (above) produces half the resistance.  Two 100 ohm resistors in parallel provide 50 ohms.
    

[papa]

       More about resistors
(In the following when I mention an Arduino pin, I mean an Arduino socket connected to that pin & labelled accordingly. I also assume an Arduino compatible operating mostly at 3.3 volts.)

Knowing what resistors can do can help us know how & why to use them in a circuit. A resistor in series with an LED (like in the Gateway schematic) limits current from burning out the LED or damaging the Arduino digital pin powering the LED. Sometimes an Arduino pin is connected (NOT in series) to a resistor & to something else like one terminal of a push button (See the DHT Node schematic below). Why? When an Arduino sketch program checks a digital pin (for making a decision), it needs EITHER a reliable zero volts meaning zero or off or false OR a reliable 3.3 volts meaning 1 or on or true. However, apparently Arduino pins can "float" or fluctuate in value even when just sitting there, causing undesired results. A pull-up or pull-down resistor stabilizes a "sitting" pin's value until something significant, like a push button press, over rides the pull-up or pull-down.

      << Click on pic for larger view.

In the schematic above, the D8 pin is connected to a push button switch that is normally open (no current flows through it yet). D8 is also connected to 3.3 volts via a 10 kilo ohm pull-up resistor. Current flows through the easiest path so when the push button is open, the resistor pulls D8 "up" to 3.3v or 1 or ON or TRUE. A push button press connects D8 to GND (now an easier path than the resistor) causing D8 to read zero or OFF or FALSE. (An Arduino sketch program should be able to test reliably if the switch was pressed or not & respond accordingly.) A pull-down resistor uses the opposite logic:  It always offers a pin a path to GND, which pulls the pin "down" to zero or OFF or FALSE, until a push button press connects the pin with (an easier path to) 3.3v & it reads 1 or ON or TRUE.

Update, 6/11/2016: To avoid needing the pull-up resistor mentioned above, see my thread Simplify End Node w Arduino internal pullup resistors.

PS The above schematic uses a 100 ohm resistor between the digital pin & the LED.  Computourist's original schematic had a 1 kilo ohm resistor.  100 ohms will work safely & make the LED much brighter.  220 ohms (also safe) will also work.

That gives two common uses of resistors.  In this case, resistance is NOT futile, but useful. ("Groan at corny joke" ;-)

[papa]

      Some comments about soldering, especially for beginners:

I believe it is wise to be cautious about soldering, at least until a circuit gets more familiar to us. I try to practice a rewording of a longtime carpenter expression: Check (schematic / instructions) twice (or more) & solder once. De-Soldering is such a time-sucking hassle & some wrong connections can damage electronic parts.

     A first try with a circuit might use a solder-less breadboard.  To leave projects more adaptable & easier to fix defective parts, I avoid some soldering & use existing plug-in sockets (like on an Arduino compatible) & may add more sockets.  I sometimes solder resistors, but otherwise plug RFM69 wires (8), transistor, Solid State Relay wires, & jumpers into sockets & may add female headers to Arduino shields. When component leads are too thin to fit securely in a socket: I enlarge them with a little solder OR I bend a socket-length of lead back on itself & crimp where the lead is bent.

     A decent set of tools helps soldering & assembling a circuit:
I followed recommendations to buy Ladyada's Electronics Toolkit & have been well satisfied (& Adafruit has not compensated me in any way). As of 3/27/2017, it's $100 plus shipping, but I found it a good selection & decent quality.  If you already have some tools, you might consider filling in listed items you do not have.  Certainly helpful is a good wire stripper, an adjustable soldering iron with a small tip, & small diameter solder.  Automatic wire strippers like this one are very convenient.

       One key to successful soldering is a stable connection between items to be soldered together.  If such items bounce or wiggle after we apply solder, we can get a poor connection, even solder in undesirable places.

    From the above Toolkit, I like & use the Panavise Jr - Circuit Board holder, but I also bought & often use one or two of these: SE MZ101 Helping Hand with Magnifying Glass.  They have articulating arms with strong alligator clips on two ends.  I use a thin piece of cardboard to protect any delicate circuit parts (like on a RFM69 wireless transceiver mini board), I must put inside the alligator clips.  One alligator clip (& thin cardboard protection) might hold a RFM69 transceiver & at a slight distance & parallel, the other alligator clip can be under & stabilizing wires to be soldered to the RFM69 mini board. Update, 5/18/2017: This Instructable & this Instructable show simple ways to make a Helping Hand more useful, like for soldering things close together & protecting delicate parts.

     Other ways (by themselves or in combination) to stabilize parts for soldering:

Gravity & pressure:  Insert parts into solder holes & try turning the board over.  That might work as you press down with the soldering iron tip.  You might need to put more thickness under some things to hold parts well.

Self Clamping:  Insert parts & on the other side, bend wire leads against the board.  If the solder hole is on a board's edge (like with RFM69 transceiver mini-boards), you might use needle nose pliers to clamp the stripped wire end back against itself.  (I do this in combination with using the Helping Hand as above.)

Clamping with spring loaded clothes pins or small heat sink clips or other clips might hold your part in place & leave room to solder.  Be careful to avoid or protect delicate parts from clips that are strong.

Sometimes one can use tape (cellophane, vinyl, NOT too-sticky duct tape) one or more ways across the top of parts.

I've also seen wall tack putty used to hold parts in place until they are soldered.

Hints to help soldering go well: Keep the soldering iron tip lightly coated with solder (Melt some on all sides & wipe any excess off on a sponge or metal scrubby pad.)  Dab the connection to be soldered with a flux pen.

How to solder circuit parts' when wire leads are too short or thin (as for DHT sensors, LEDs, resistors)? Twisting them together comes apart easily or creates a lump when soldered.  Here's where I find a Helping Hand (HH) very helpful.  I put the HH's two alligator clips at the top, parallel & a little apart from each other.  For example, I insert a resistor's wire lead into one alligator clip pointing toward the other clip.  Then I insert the LED wire lead into the other clip pointing toward the first. I move the wire leads & clips until a short distance of the two wire leads touch each other & overlap.  That overlapping area solders very well for me.

    How to tell if one successfully soldered desired parts & not elsewhere:  It's good to check for success frequently & fix mistakes while soldered parts are more accessible. Visually:  At least for through solder hole parts, one wants a mini mountain of solder around where the wire lead exits the board. With a magnifying glass, see if solder covers desired parts & avoids nearby locations.  Wiggle it a bit (better for bad connections to come apart then).

    A great tool for testing that the right connections are made & other things is a digital multimeter (DMM) like that in the Ladyada kit above, particularly the continuity test setting. On the DMM dial the continuity setting symbol looks like a diode symbol or a sound waves or wifi symbol or musical notes or a combination of these.  When at that setting & you touch the probe ends of the two DMM wire leads, you hear a tone & (or maybe see a LED light).  Such a tone tells you the two probes are touching two places that are electrically connected.  No tone means NOT electrically connected.  After you solder something, touch one probe on it & the other probe to another place the part is supposed to be connected.  Hear a tone & it's good. Likewise with the two probes, touch two places nearby that should NOT be connected.  In this case, no continuity tone is good.  Cautions: don't expect to find continuity through a resistor or capacitor or a closed switch. You may need to rub a probe around on a soldered area before you find it is indeed connected.

DMMs are good for other things like confirming voltages & the size of resistors.  I used mine with a prototyping shield to tell what things are connected & NOT & what might be connected for my purposes.  That's how I was able to improve the shield for my purposes (as described above) like add more 3.3 volt connections.

Heat Shrink tubing is something else I appreciate & use often to protect bare areas from shorting, to help stabilize & strengthen, make more attractive, & to color code an electronic purpose (red for power, black for ground, etc).  I keep a ready supply of tubing, especially 3/32 inch diameter in various colors. Place tubing BEFORE soldering, etc. blocks your placing it, but try to keep tubing away from the area to be soldered or the tubing may shrink too soon.

Only our imagination is the limit on ways to solder & assemble circuits.  What other soldering tricks have you seen or invented?

[papa]

     

I bought some of these spring loaded metal hair clips.

        Possible uses:

- After inner surfaces are insulated (electrical tape??), clamp programming jig over chip pads.

- After inner surfaces are insulated, clamp small wires for strain relief.

- In tight spots, hold wires stable for soldering.

[papa]

What other circuit-related matters would be good to post here?

[greginkansas]

Sept 24, 2015 17:55:47 GMT papa said:

     
Schematics specify a resistor's ohm size.  Often other sizes will work, but maybe not as well.  Connecting resistors in series (one after another) creates one resistor unit that sums all their ratings, i.e. two 100 ohm resistors in series makes 200 ohms. This is one way to create what we need from available parts. Connecting two equal resistors in parallel (above) produces half the resistance.  Two 100 ohm resistors in parallel provide 50 ohms.
    

Might want to check this one PAPA.
resistors in parallel gives twice the current capacity.
Two 100 ohm resistors in parallel provide 100 ohms.

[papa]

Thanks, greg, for checking my postings.  I checked again. At this online calculator, I plugged in two parallel resistors of 100 ohms & got 50 ohms.

     
I also used the formula from here with two parallel resistors of 100 ohms & calculated 50 ohms

As you say "resistors in parallel give twice the current capacity," but more current flow with the same voltage means that the total resistance of two parallel 100 ohms resistors is less than the resistance of one 100 ohm resistors.  Twice the current capacity offers half as much resistance to current flow.

Three 100 ohm resistors in parallel provide 100/3 or 33 1/3 ohms.  These quick calculations only work if the parallel resistors are equal in value.  If they are not equal in value, one must use the formula.

I believe I am correct about parallel resistors of equal value, but always desire to correct mistakes if they are explained to me.

[computourist]

Hi papa ,

You really take an effort in explaining things to newbies. Good work !

I have one remark. In an earlier post you stated:


Some things about schematics that I had to learn: a) Some things in a schematic may not mean anything, but may result from how the drawing was created. To my knowledge, the "dots" on the lines in CompuTourist's Gateway schematic (which I edited) do not mean anything.

These 'dots' are in fact quite significant. A dot on an intersection of lines means they are interconnected. An intersection without a dot are lines crossing, but not connected.

For clarification, have a look at the following post:
electronics.stackexchange.com/questions/28251/rules-and-guidelines-for-drawing-good-schematics

In particular item 11 will help:


Dots connect, crosses don't

Draw a dot at every junction. That's the convention. Don't be lazy. Any competent software will enforce this anyway, but surpringly we still see schematics without junction dots here occasionally. It's a rule. We don't care whether you think it's silly or not. That's how it's done.


Hope this helps and keep up the good work !

Rgds,
Computourist

[papa]

Thanks, computourist, for explaining the meaning of dots on schematics. Not knowing this, I had to use different colored wires to indicate non-connected wires that cross each other. I corrected the note above.

Thanks also for compliment on my helping newbies. I hope the forum is also still a good place for more advanced users (like you) to lead us into new developments.

Good to hear from your wisdom & knowledge. I was missing you lately. Drop in when u can.

[greginkansas]

Jul 31, 2017 23:35:29 GMT greginkansas said:

Sept 24, 2015 17:55:47 GMT papa said:

     
Schematics specify a resistor's ohm size.  Often other sizes will work, but maybe not as well.  Connecting resistors in series (one after another) creates one resistor unit that sums all their ratings, i.e. two 100 ohm resistors in series makes 200 ohms. This is one way to create what we need from available parts. Connecting two equal resistors in parallel (above) produces half the resistance.  Two 100 ohm resistors in parallel provide 50 ohms.
    

Might want to check this one PAPA.  resistors in parallel gives twice the current capacity.  Two 100 ohm resistors in parallel provide 100 ohms.

Aha, right I was was thinking of capacitors. The mind slips when you get old

papa:  However, a person willing to admit an error shows wise humility.

[brump]

Associations of series resistors





The association of resistors in series consists of connecting the "output" of one resistor to the "input" of another in a circuit. Each additional resistor placed in a circuit adds up to the total resistance of that circuit.

The formula for calculating a total of n series-connected resistors is:  Req = R1 + R2 + ... Rn

That is, the resistor values ​​of the series connected resistors are simply summed. For example, if we were to find the equivalent resistance in the image below

In this example, R1 = 100 Ω and R2 = 300Ω are connected in series. Req = 100 Ω + 300 Ω = 400 Ω

Association of resistors in parallel





The association of resistors in parallel is when the "inputs" of 2 or more resistors are connected together, and the "outputs" of the resistors are connected to each other.

The equation for a total of n resistors in parallel is:  Req = 1 / {(1 / R1) + (1 / R2) + (1 / R3) .. + (1 / Rn)}

Let's look at the following example. Given R1 = 20 Ω, R2 = 30 Ω and R3 = 30 Ω.

The total equivalent resistance for the 3 resistors in parallel is:

Req = 1 / {(1/20) + (1/30) + (1/30)}

= 1 / {(3/60) + (2/60) + (2/60)}

= 1 / (7/60) = 60/7 Ω = approximately 8.57 Ω.

Circuits combining series and parallel resistor associations




A combined network is any combination of series and parallel circuits connected forming so-called "equivalent parallel resistors".

        Check out the example below.

We can see that the resistors R1 and R2 are connected in series. Therefore, their equivalent resistance (we will highlight it using Rs) is as follows:

Rs = R1 + R2 = 100 Ω + 300 Ω = 400 Ω.

Then we can see that the resistors R3 and R4 are connected in parallel. Therefore, the equivalent resistance of them (we will detach it using Rp1) is as follows:

Rp1 = 1 / {(1/20) + (1/20)} = 1 / (2/20) = 20/2 = 10 Ω

Then we can conclude that the resistors R5 and R6 are also connected in parallel. Therefore, the equivalent resistance of them (we will detach it using Rp2) is as follows:

Rp2 = 1 / {(1/40) + (1/10)} = 1 / (5/40) = 40/5 = 8 Ω

Now, we have a circuit with resistors Rs, Rp1, Rp2 and R7 connected in series. Hereafter, they can be summed to obtain the equivalent R7 resistance of the network we had at the beginning in the process.

Req = 400 Ω + 20Ω + 8 Ω = 428 Ω.

Interesting facts

Understand resistance: Every material that conducts electric current has resistivity, which is the resistance of a material to the electric current.

The resistance is measured in ohms. The symbol used for this measurement is Ω.

Resistance properties vary by material.

Copper, for example, has a resistivity of 0.0000017 (Ωcm)

Already the ceramic has a resistivity around 10 14 (Ωcm)

The higher the number, the greater the resistance to electric current. You can see that copper, which is commonly used in electrical wiring, has a very low resistivity. Pottery, on the other hand, is so resistive that it serves as an excellent insulator.

The way you join wires of varying strengths makes a lot of difference in the overall performance of a resistive network.

V = IR.

This is Ohm's law, defined by Georg Ohm in the early 1800's. If you know the value of at least two of the variables in this equation, you can easily calculate the value of the third.

V = IR: The voltage (V) is the product of current (I) * resistance (R).

I = V / R: The current is the voltage quotient (V) ÷ the resistance (R).

R = V / I: The resistance is the quotient of the voltage (V) ÷ the current (I).

        Tips:

Remember, when the resistors are in parallel, there are many different paths to an end, so the total resistance will be less than each path. When the resistors are in series, the current will have to travel through each resistor, so the individual resistors will be added together to give the total resistance to the series.

Equivalent resistance (Req) is always less than the smallest contributor to a parallel circuit, and is always greater than the largest contributor to a series circuit.

        Papa:  Thanks, brump, for a thorough exposition of resistors.

[papa]

Adding, Improving, or Fixing Insulation

Insulation is important to prevent current from flowing where it is not wanted, including our avoiding electrical shocks.

As I wrote above, homeautomation.proboards.com/post/446/thread

Heat Shrink tubing is something else I appreciate & use often to protect bare wire areas from shorting, to help stabilize & strengthen, make more attractive, & to color code an electronic purpose (red for power, black for ground, etc). I keep a ready supply of tubing, especially 3/32 inch diameter in various colors. Place tubing BEFORE soldering, etc. blocks your placing it, but try to keep tubing away from the area to be soldered or the tubing may shrink too soon.

For a better seal in challenging installations (like outdoors), brump recently recommended

As brump recently mentioned, Liquid Tape is a helpful product available online & in some home supply stores. Liquid tape comes in a paint on or spray on form. One can apply it to seal an exposed wire from oxidizing or shorting.

[papa]

    Adding, Improving, or Fixing Insulation

Insulation is important to prevent current from flowing where it is not wanted, including our avoiding electrical shocks.

As I wrote above,

Heat Shrink tubing is something else I appreciate & use often to protect bare wire areas from shorting, to help stabilize & strengthen, make more attractive, & to color code an electronic purpose (red for power, black for ground, etc). I keep a ready supply of tubing, especially 3/32 inch diameter in various colors. Place tubing BEFORE soldering, etc. blocks your placing it, but try to keep tubing away from the area to be soldered or the tubing may shrink too soon.

For a better seal in challenging installations (like outdoors), brump recently recommended heat shrink tubing with a glue lining.  Dow Corning 4 Electrical Insulating Compound will allow one to coat metal to prevent oxidizing.

As brump also recently mentioned, Liquid Tape is a helpful product available online & in some home supply stores. Liquid tape comes in a paint on or spray on form. One can apply it to seal an exposed wire from oxidizing or shorting.