Best kits? (and various other questions) - Page 1
Forum section: electronics / beginners

author: Retkid
author_rank: Newbie
timestamp: April 26, 2019, 03:12:04 am
content: Well I'm getting to the point where I can start to design concepts. Im very fuzzy on transistors and dont quite understand NPN AND PNP.https://cdn.discordapp.com/attachments/504691699872694273/571113686509289473/unknown.pngI'm at the level at apart from the transistors, and how everything feedbacks into each other, I get it pretty well (also the resistor with the diode, what the hell is that)but anyway, any suggestion for component kits. I'm planning on getting a de soldering iron and going picking for old pcbs to nab resistors and non electrolyritic caps. I was wondering if i can take an old PCB, cut the top laye with the solder mask off, then draw traces and photo-resist traces onto a used pcb, as well.Any of these questions, i would appreciate any answers to any of my questions

author: David Cutcher CEG
author_rank: Contributor
timestamp: April 26, 2019, 06:09:10 am
content: I am currently putting together an introduction course to be presented on Udemy.comIt isspecifically for the rank beginner, who is interested in learning electronics, but like many people, don't know where to begin.My biggest asset is that I approach this as a teacher, not from the technical point of view. Hands on right from lesson 1, and 1st circuit in lesson 3.The beta test course will be up and running June 1st.However, Right Now, I am looking for a few more beta testers.If you are already into electronics, this is not for you.Newbies only, please.My explanations are not deeply technical, but technical enough.If you are interested, send me a note. My email address is in the header of the attached outline.

author: DDunfield
author_rank: Regular Contributor
timestamp: April 26, 2019, 01:02:02 pm
content: Quote from: Retkid on April 26, 2019, 03:12:04 amAt a very basic level: Transistors are unidirectional devices. eg: In a common-emitter configuration, a small current between base and emitter controls a larger current between collector and emitter. But ONLY if the currents are flowing in the right direction. Think of NPN and PNP as the "polarity" of the transistor. In the above example an NPN transistor would have the base (and collector) at a more positive voltage than the emitter in order for current to flow in the right direction. For a PNP transistor, the base (and collector) would be more negative than the emitter.Quote from: Retkid on April 26, 2019, 03:12:04 amAre you referring to the device at the bottom of the image which looks like a horizontal resistor with a triangle connection coming off the bottom mid-way?If so, that is a potentiometer, although in this case it is being used as a rheostat.A rheostat is simply a variable resistor. Mechanically one connection is at the end of a resistive material, and the other can slide along the material. The closer to the connected end, the lower the resistance, the further away, the higher the resistance.A potentiometer is just a rheostat with a connection at the other end as well. As the tap connection slides the resistance to one end lowers while the resistance to the other end raises.In this case, since the "far" connection is connected to the tap it serves no extra purpose and could be left unconnected (*).(*) The advantage of connecting the far end to the tap is that if the sliding connection between the tap and the resistive material becomes intermittent (common in some pots as the device ages and/or dust gets inside). the rheostat will present it's maximum value instead of "open circuit".Btw, I can't see where it goes, but assuming the dotted line going from the tap on the potentiometer goes to another tap on another potentiometer, this means it's a "ganged" pot. In other words, two (or more) potentiometers which operate in tandem from a single shaft. An example being the volume control of a stereo amplifier. You want to control the gain of two independent circuirs (left and right) with a single control.Dave

author: rstofer
author_rank: Super Contributor
timestamp: April 26, 2019, 02:12:32 pm
content: As to transistors, this tutorial is as good as any other. There's a nice animation about 1/2 way down the page and it really demonstrates switching action very well.https://learn.sparkfun.com/tutorials/transistors/allI haven't spent much time with Sparkfun tutorials but from what I see, they are pretty good.Digilent has a more formal program called RealAnalog - heavy into the math behind all this stuff.

author: Retkid
author_rank: Newbie
timestamp: April 26, 2019, 03:02:15 pm
content: Quote from: DDunfield on April 26, 2019, 01:02:02 pmThanks for the term rheostat, much better than "Pot that's in parallel in a way to change the current".How do i wire ganged pots? and I cant find a Transistor with the arrow on the top IN EasyEDA...

author: rstofer
author_rank: Super Contributor
timestamp: April 26, 2019, 06:11:14 pm
content: Quote from: Retkid on April 26, 2019, 03:02:15 pmI don't use the software and the online version is a PITA but... You can rotate a part as you place it by typing R or hitting the space bar. I don't know how to mirror it but I suspect there is a keyboard shortcut for that as well.Maybe there is a manual...

author: Retkid
author_rank: Newbie
timestamp: April 26, 2019, 07:28:51 pm
content: Ah, i wasn't thinking that the input can come from either left or right, Thanks!

author: DDunfield
author_rank: Regular Contributor
timestamp: April 26, 2019, 07:47:48 pm
content: Quote from: Retkid on April 26, 2019, 03:02:15 pmGanged pots are wired just like two independent pots (assuming a dual ganged pot).The connection between them (represented by the dotted line in your image) is purely mechanical, so that when you adjust one, you adjust the other.Think of a stereo system with a left and right amplifiers. These could be completely independent with separate left and right volume controls, but if you could mechanically tie them together to a single knob on the front panel, it would seem like a single control, even though you are adjusting two pots.Dave

author: Retkid
author_rank: Newbie
timestamp: April 27, 2019, 12:28:50 am
content: Quote from: DDunfield on April 26, 2019, 07:47:48 pmDave, can you find like a video or something on it? I cant really find anything.

author: DDunfield
author_rank: Regular Contributor
timestamp: April 27, 2019, 02:47:28 am
content: Quote from: Retkid on April 27, 2019, 12:28:50 amI'm sure there are tutorials around on the net, but I've never looked for anything as this is stuff I learned 45 years ago.I'll do my best to provide some insight.Please forgive my crappy drawings, I don't have a drawing editor on this system, so I used a little DOS one I wrote about 30 years ago to send simple drawings over Fidonet.A pot is normally used as a variable voltage divider.Consider the attached drawing RESIST.JPG this shows a simple resistive voltage divider: VOUT is VIN x R2 / (R1+R2)A pot basically allows you to change the R1 and R2 values. For example, a 10K pot will always have (R1+R2) = 10k, but R1 and R2 can be any combination that adds up to 10k,So.. for VIN = 10voltsif R1 = 10k and R2 = 0k, then VOUT = 10 x 0 / 10 = 0 Volts.If R1 = 9k and R2 = 1k, then VOUT = 10 x 1 / 10 or 1 volt.if R1 = 5k and R2 = 5k, then VOUT = 10 x 5 / 10 or 5 volts.If R1 = 1K and R2 = 9k, then VOUT = 10 x 9 / 10 or 9 volts.If R1 = 0k and R2 = 10k, then VOUT = 10 x 10 / 10 or 10 volts.Thus you can take the signal into an amplifier and divide it down to any lower value you like, thereby effectively controlling the gain of the amplifier.The majority of pots are rotary, although there are other types (eg: linear such is used on equalizers, DJ mixers etc.)I've tried to give an idea of how a rotary pot is constructed in POT.JPGThe resistive material is arranged in an arc, with a terminal at each end, and a wiper attached to the center tap terminal. As the control knob is turned, the wiper moves around the arc, adjusting the point at which is contacts the resistive material. In the above discussion R1 would be the resistance of the material between the wiper and one end terminal, R2 would be the resistance of the material between the wiper and the other end terminal.POTS.JPG contains a photo of some actual pots from my junkbox.On the left is a pot with the back off. You can see the resistive material and the wiper. Although you can't see the shaft, it comes out directly from the center (look at the others).This happens to be a "wire wound" pot, which means the resistive material happens to be a coil of fine nichrome "resistance" wire wrapped around the arc shaped form, but that doesn't matter for this discussion (I chose it because it is easy to see the arc and wiper).The center pot is a typical panel mount single pot, you should be able to imagine how it works having seen the left one.The pot on the right is a dual ganged pot. As you can see it is simply two single pots attached together. The shaft passes through the first pot and enters the second exactly as it would in a single pot. The two sets of three terminals are electrically independent. As far as any circuits are concerned, this is two separate pots - the only connection is the mechanical one caused by sharing the same shaft.Hopefully this will all make sense...Dave

author: rstofer
author_rank: Super Contributor
timestamp: April 27, 2019, 02:28:07 pm
content: Dual pots don't always share the same shaft. In the old days there were many applications for concentric shaft potentiometers.I made a quick pass at Digikey and didn't find any dual or stackable pots. Probably because today we would be using rotary encoders.

author: Retkid
author_rank: Newbie
timestamp: April 27, 2019, 06:46:54 pm
content: Quote from: DDunfield on April 27, 2019, 02:47:28 amAh thanks for the explanation and the picture. Dual Ganged pot im going to assume is an older word for it as I cant find anything on it.This makes a lot of sense, i would of been fiddling with that for a while Eseentiallly it will always be 10k, the only thing that changes is the "mixing" of the signals. I really appreciate your explanation!

author: David Cutcher CEG
author_rank: Contributor
timestamp: April 27, 2019, 06:58:28 pm
content: Just an animated gif file of how the pot works.David Cutcher "Certified Evil Genius"

author: DDunfield
author_rank: Regular Contributor
timestamp: April 27, 2019, 07:18:04 pm
content: Quote from: rstofer on April 27, 2019, 02:28:07 pmYes, just because a pot has two "bodies" on what looks like one shaft doesn't mean it's the ganged type we have been discussing ... sometimes It is actually two shafts which come out to a knob and an independently adjustable ring. This is called concentric.And there are other types of pots too... Attached is another photo of more really old crap from my junkbox (more of a junkbasement really):1st row: Samples of concentric pots. Note that you can see the smaller inner shaft sicking out past the end of the larger outer shaft (really a tube). The inner shaft rotates the wiper in the body furthest from the mount, the tube rotate the one closest to the mount.The third one over shows a couple extra features you can have on a pot. It has a switch on the back, this how devices with click-ON, then adjust volume work. It also has a tap on the bottom, this is a connection to a point on the resistive material at some set position between the two ends. Think of it as another wiper that does not move (always in the same place).At the end of the first row, I have placed a rear view of the "inside" pot, the one closest to the mount. You can see that the center is hollow allowing the tube from the "outer" pot to pass through, and you can also see the slots where the tabs from the outer body would connect, fixing the outer body in place.2nd row: These are linear pots - these adjust by moving the actuator along the length of it, and as you might expect, the resistive material is just a straight line with the wiper fixed to the actuator sliding along it.3rd row: The first two are "precision" pots. In these, the resistive material runs from front to back, and the wiper is moved by a screw attached to the shaft. It takes many turns (as many as there are threads on the screw) to move the wiper from one end to the other, making for much finer adjustment than a single-turn pot.The last pot on the 3rd row is an example of a dual ganged pot which has only one body, with two sets of resistive material and wiper being attached at each end of that body. It functions exactly as one with two bodies.Dual ganged pots used to be VERY common in the volume and tone controls of stereo amplifiers, receivers etc.The are much less common these days for two main reasons:1) Stereo is less common these days ... most receivers/amps do more channels, 5 and 7 being very common. It is easier and more inexpensive to control them via software controlled gain pads with an encoder to interface to the user than it is to build 5 and 7 tier ganged pots.2) Everybody wants to control their gear remotely, not just with a traditional I/R remote, but from their phone or tablet. Controlling physical pots requires a motor and gears implemented in a way which does not resist manual adjustment .. you used to see this on high end stereo gear, but again software controlled gain pads are easier, less expensive and more reliable.There are other reasons as well, pots have maintenance problems - they get dirty and noise. "Most everything" has a computer in it now, which makes electronic control much more feasible than when all you had was a few transistors.Dave

author: Retkid
author_rank: Newbie
timestamp: April 27, 2019, 07:36:34 pm
content: Quote from: DDunfield on April 27, 2019, 07:18:04 pmThanks I really appreciate this. This explains a lot. I think it could of been explained easier on the shcematic. This would of taken me a very long time to figure out. I appreciate you immesnely.