Simple  elec. - Page 1
Forum section: electronics / beginners

author: joesam
author_rank: Contributor
timestamp: February 14, 2021, 12:16:48 am
content: Hello , Beginner doesn't describe My Electronic knowledge- 80 years old and have tried to do accomplish to much to late it seems. I will show the project I am into, and cannot achieve success in having it work.I am using a 14500 battery rather than a coin cell, I wanted to add a solar P to recharge.I am using a wired battery case to simplify the project.I have wired the transistor- as relates to the PIR and the flashing LED along with the 1k Resistor as stated in schematic- I in my lack of elec. wisdom believe the battery power is fault.If I am a bother , I understandJoe

author: bdunham7
author_rank: Super Contributor
timestamp: February 14, 2021, 12:24:47 am
content: OK, just so we're clear, the idea is that you want the red LED to be powered up when there is no light, in other words you want the phototransistor to turn the 2N3904 off, right?To start then, what is the part number of the phototransistor and why did you select 1K as the value of the resistor?

author: joesam
author_rank: Contributor
timestamp: February 14, 2021, 12:47:18 am
content: Here are our components: On top: a CR2032 lithium coin cell (3 V). On the bottom (L-R): the LED, an LTR-4206E phototransistor, a 2N3904 transistor, and a 1 k resistor.You have entered a world You didn't know existed. Thank You for being Kind.I thought My attch, was in my orig. post- I see the Schematic won't copy so I am at a loss for that, The plan is what The author calls a "Throwie" Yes I am trying to replicate a Dusk to dawn , would love to add a solar panel. If i'm to much to bother with, is ok to pass on trying

author: james_s
author_rank: Super Contributor
timestamp: February 14, 2021, 01:13:06 am
content: Did you design this circuit or did you find it somewhere?The most obvious problem I see is the lack of a current limiting resistor for the LED. The transistor is also in an unusual configuration, it appears to be an emitter follower rather than the more typical configuration as a low side switch.

author: joesam
author_rank: Contributor
timestamp: February 14, 2021, 01:32:15 am
content: Thank YouI googled the Circuit, "MadEvilscientist" Simple Led D't'D project- I have tried the transistor wiring both ways + To Trans collector pin then reversed to + to trans- emitter pin . leaving the Transistor base pin to connect the resistor and Ltr - as shown. I wired the resistor as shown both time following Positive + to base pin and base pin joined to collector of LTR--

author: Algoma
author_rank: Frequent Contributor
timestamp: February 14, 2021, 01:44:27 am
content: A breadboard would be helpful to troubleshoot..According its datasheet, that photo diode is designed to react mostly to Infrared Light.

author: Electro Fan
author_rank: Super Contributor
timestamp: February 14, 2021, 01:50:39 am
content: Hi joesam,Welcome to the EEVblog forums. We are delighted to see you here working on your projects. You have come to the right place. Keep up the good questions and answers and people here will be happy to help you!

author: DrG
author_rank: Super Contributor
timestamp: February 14, 2021, 03:09:03 am
content: Quote from: joesam on February 14, 2021, 01:32:15 amSo that everyone is on the same page, here is a link to the projecthttps://www.evilmadscientist.com/2007/a-simple-and-cheap-dark-detecting-led-circuit/@joesam, you are not a bother at all...so long as you end up with a working projectI hate to be a pessimist, but when you are building something very simple, but are truly a beginner, some things that you might not think matter, might matter a lot. For example, you are not using a 3V coin cell but a 3.6V battery that has a much bigger punch than that little coin cell (1'm seeing them at 1500 mAh and similar vs. maybe 210 mAh for the cr2032. That can make a difference when there is no current limiting resistor as can when you have changed connections on the trans.No matter. You can get this thing working. Can you get us a picture ofyourcircuit? Do you have any other components - more resistors and transistors and so on?I would suggest you go step wise - first trying to light the LED with the battery and a resistor...then with the transistor and so on.

author: james_s
author_rank: Super Contributor
timestamp: February 14, 2021, 05:36:59 am
content: Yeah it's not uncommon to see a CR2032 driving an LED directly, relying on the internal resistance of the battery. It's not a very good idea but it does work, however if you sub a larger battery it will usually burn out the LED.

author: joesam
author_rank: Contributor
timestamp: February 14, 2021, 12:08:23 pm
content: Thanks for the support for Simple Project- I have followed the Path of the circuit step - step with meter, I would let You all know You cannot burn out the LED the Circuit calls for with a 9 volt battery using the 9 directly to the Led. I will pick up the cell batt today and try that. I was hoping to modify the project to have a solar panel power the unit . I have to get to first base first. Thanks

author: james_s
author_rank: Super Contributor
timestamp: February 14, 2021, 06:58:56 pm
content: Why don't you just put a resistor in series with the LED to limit the current and then you don't have to worry about it? Calculating the series resistor for an LED using Ohms Law is one of the very basic things that all beginners should learn proficiently. You will need Ohms Law constantly.

author: Zero999
author_rank: Super Contributor
timestamp: February 14, 2021, 07:19:33 pm
content: If you want to run if off 9V, then you need to have a resistor in series with the LED, and the base resistor should also be increased.Putting the LED in series with the collector, will give a sharper turn on/off, rather than a gradual transition, if that's what you prefer.

author: alsetalokin4017
author_rank: Super Contributor
timestamp: February 14, 2021, 07:30:44 pm
content: In the OP the LED is referred to as a "flashing LED" and later on the OP says the LED won't burn out if fed 9v directly without a current-limiting resistor. So... this is NOT just a plain old red LED that the OP is using in the project, is it? For this circuit you want an ordinary plain old LED without its own builtin circuitry.Also that phototransistor is an IR pt, is it not? Perhaps one would want to use a visible light pt for this project.

author: Zero999
author_rank: Super Contributor
timestamp: February 14, 2021, 07:37:35 pm
content: Yes, some flashing LEDs have built-in current limiting, but it should have said so on the schematic. I also added the 0V node, which I admit is a little picky, but by convention, all circuits should have a 0V reference.

author: alsetalokin4017
author_rank: Super Contributor
timestamp: February 14, 2021, 08:08:01 pm
content: I have built the circuit on a breadboard just now, using the component values in the OP, except I couldn't find a 3904 so I used BC337-25. It works, but the IR photodetector needs a good strong source of IR radiation to make the LED turn off. My IR remote controls can do it but it really likes my radiant electric heater. Show the heater's glowing element to the IR pt and the LED turns off cleanly. It does _not_ work with plain old ambient visible light, the LED just stays on. This is the Photodiode's fault, you need a visible light one.SO... Make sure the LED you are using is a plain ordinary LED without "features". Make sure you have the IR PT in the correct polarity. (Ditto the LED).

author: Electro Fan
author_rank: Super Contributor
timestamp: February 14, 2021, 08:27:58 pm
content: Quote from: joesam on February 14, 2021, 12:08:23 pmHi joesam,As you can see lots of good helpful advice here. Hope you are having as much fun as the rest of us.alsetalokin4017 raises a good point – it’s not clear if you have a plain red LED or something else.You might be pretty far down the path on all this and have things nearly sorted out, but if not here are some additional thoughts.It might be worth just starting by experimenting with powering a plain red LED. If you do this, I think you will find that at about 1.8 volts a typical (5mm red) LED will light with just 1 milliamp (mA). (If you have access to a variable power supply you can set the power supply for 1.8 volts and 1 mA and see the LED light. As you turn up the allowable current the LED will get brighter and then somewhere above 20 mA the LED will burnout. So it is possible to light a LED directly without a resistor but generally a resistor is recommended to protect the LED from too much current.)If you look at the specs for a 9V battery you will see that it can deliver 2mA for 350 hours, but it can also deliver 250mA for over 8 hours. For a second the 9V battery can deliver way more current than a red LED can withstand. To persuade yourself of this just sacrifice one LED by connecting it directly to a 9V battery and you will see that the LED will burnout instantly.https://www.duracell.com/wp-content/uploads/2016/03/MN1604_US_CT1.pdfAfter trying a few direct to battery experiments (it might be good to have several LEDs on hand) try powering the LED with a battery and a resistor. A lot electric theory requires some math and some of the math can be a bit complex but if you are not already familiar with the theory and if you are up for it I'd highly recommending looking at Ohm's Law.https://www.electronics-tutorials.ws/dccircuits/dcp_2.htmlThe pyramid and wheel charts don't require much math (mostly just multiplication and division) and they are super helpful. I realize your "Simple elec." post is probably mostly to solve a practical problem of turning something on and off for a particular project but if you have an interest in electricity and electronics (which can be pretty fascinating) learning and applying Ohm's Law is perhaps the gateway to everything. With Ohm's Law and experimenting with LEDs and resistors and batteries, you can learn a ton. The key other items that might be helpful would be a simple DMM (Digital MultiMeter that can be had on Amazon for about $10), and a calculator or a spreadsheet, or just a pencil and paper. When you see the relationships between volts, amps, and ohms it becomes pretty exciting. Along the way keep an eye on watts too (volts x amps = watts); at some point you might find that you kept the current low enough for the LED but the resistor burned up.... that will be when you start becoming more interested in watts.Here is a good article on LEDs:https://www.electronics-tutorials.ws/diode/diode_8.htmlCheckout the curve titled: Light Emitting Diodes I-V Characteristics. Keep in mind "Forward Voltage" as you do experiments and the math calculations.One other thing you can try (as you have already found) is a 2032 battery. Here is a spec sheet:https://data.energizer.com/pdfs/cr2032.pdfI think at 3V you will find that this battery will supply enough current to light the LED but won't burn it out. If you keep experimenting with different combinations of values, measure with a DMM, and look at the spec sheets I think you will find the relationship between what you observe and what the math shows is pretty cool.With the battery, LED, and resistor measurements squared away the transistor experiments start to become more accessible. Enjoy!fwiw, your "Simple elec." project is an excellent learning project!If you can not only hook these things up and make them work but explain the measured values with the concepts and the math you are on your way to a great journey.PS, big sorry if this stuff is too basic and you are beyond all of it - in which case carry on

author: DrG
author_rank: Super Contributor
timestamp: February 14, 2021, 08:37:08 pm
content: Note a few of the designer's comments:https://www.evilmadscientist.com/2007/a-simple-and-cheap-dark-detecting-led-circuit/To give the quick set of answers to some of the popular questions:This it is a special set of parts that is chosen to work well together, and several simplifications have been made on the basis of which particular components are used– for example, we rely on the internal resistance of the coin cell, so that we don’t need an external current-limiting resistor.Because of this, there aren’t many simple direct substitutions that work well.There are plenty of great CdS (“LDR”) phototransistor circuits out there. For better or worse, this is not one of them. (We happen to think betterfor a number of reasons.)You can’t just substitute a white (or UV, or blue, etc) LED directly, because there isn’t enough voltage to drive it well. (We did actually show how to do this one– see below.)You can’t just substitute 12 V, because the current will be too high, and will blow out your LED. Yes, there are ways to do it, but you have to think it through.Some other phototransistors will work, and some will not. If you would like to know which, you can compare their datasheets, or– better yet –just try it!But for the TS, hey, that's part of the fun - figuring what works and why and what does not work and why.

author: joesam
author_rank: Contributor
timestamp: February 14, 2021, 10:56:55 pm
content: Sunday wasn't so boring after all . Y'all are very kind, thank You,As Several have noted and a Gentleman even produced a similar device, I have a couple of "'To You all" glaring errors in the parts I am using. The Led and the light cell will have to be replaced with parts of lower values to meet the Authors success he had with his device. My goal was to make a flasher using 3.7 volts rechargeable --and a solar driver to keep battery charged. I will do a follow up. once I purchase the pieces I need. Yes I could have bought , But Covid's home bound boredom is driving me to find new adventures. Again Thanks

author: joesam
author_rank: Contributor
timestamp: February 14, 2021, 11:03:36 pm
content: I actually wondered why 9 wouldn't kill the entire system , I now understand (I think) - I started with 14500 thinking I could get by. So I will return to "start' and do the Low amp Led, change the Phot-ores- make the device work and increase the value of the pieces to crank up the voltage as I learn . Thank You

author: joesam
author_rank: Contributor
timestamp: February 14, 2021, 11:10:42 pm
content: You are correct in all You observations, The only thing is I was using 9 volt because the lower voltage batt-didn't turn the led on- I probably blew out a couple of transistors and Photocells, I trashed all except the 1ks and started anew each time though. Thank You ,

author: DrG
author_rank: Super Contributor
timestamp: February 14, 2021, 11:19:16 pm
content: Quote from: joesam on February 14, 2021, 11:10:42 pmWhen you want to direct your response to a particular message, just use the quote button. That will copy the message into your new message and you can type away. That's how I did this one.

author: DrG
author_rank: Super Contributor
timestamp: February 22, 2021, 05:24:39 pm
content: @joesam - you still with the project?

author: joesam
author_rank: Contributor
timestamp: February 22, 2021, 05:35:57 pm
content: Quote from: DrG on February 22, 2021, 05:24:39 pmYes, But Mail has lost ( I assume or just delayed) my order of pieces I was advised to change over to , from my initial startup ones.- Thank You for asking.

author: DrG
author_rank: Super Contributor
timestamp: February 22, 2021, 05:42:18 pm
content: Quote from: joesam on February 22, 2021, 05:35:57 pmGood deal. I have also seen significant delays in USPS package handling. I track them and it is not unusual to see something stuck for ~5 days - but you could also be dealing with something specific (e.g., Texas). Hope to see your next report soon

author: rstofer
author_rank: Super Contributor
timestamp: February 22, 2021, 07:10:42 pm
content: Quote from: joesam on February 14, 2021, 10:56:55 pmWelcome to the hobby!There is a process in computer science known as "Stepwise Refinement" coined by the eminent Niklaus Wirth. It applies in just about every other field as well.Get something to work and then incrementally improve it. This is a great way to learn. Follow the author's directions with no changes whatsoever. Then substitute for the sensor. Later, substitute for the battery. Finally add the solar panel. Step by step, refining at each.I don't know where you are at with the 'theory' but Ohm's Law is the most basic and most commonly used relationship between voltage, current and resistance. There are plenty of tutorials and videos. Take a 9V battery and some resistors of various values and measure the voltage and current. Then see how accurate the resistor is by computing resistance. Put some resistors in series and see how a 'voltage divider' works. Finally, put some resistors in parallel and measure the branch currents. This will also get you plenty of experience with your DMM.A bit later on, look into Kirchhoff's Laws. You can't even start with op amps without at least a superficial understanding of Kirchhoff's Current Law, often called just KCL.It's going to take time but the one thing we have right now is time. Lots and lots of time...If you want more on transistors, Google for 'w2aew transistor' and see what's available. Alan Wolke does a great job with his videos. eevBlog (Dave) also has videos on the topics, usually filed under "Fundamental Fridays".Again, welcome!

author: rstofer
author_rank: Super Contributor
timestamp: February 22, 2021, 07:14:51 pm
content: If you're up for a little reading, any of the Forrest Mim's books are excellent but here the place to starthttps://www.amazon.com/Getting-Started-Electronics-Forrest-Mims/dp/0945053282

author: joesam
author_rank: Contributor
timestamp: February 22, 2021, 07:43:09 pm
content: Quote from: rstofer on February 22, 2021, 07:10:42 pm

author: rstofer
author_rank: Super Contributor
timestamp: February 22, 2021, 08:25:14 pm
content: Like any group of people, individual skills vary. Many of the members here are beginners. Some are technicians, some are engineers and I wouldn't be surprised if some are instructors/professors. Skills will vary all over the map. But everybody started with Ohm's Law!In terms of arithmetic/math, it's mostly add, subtract, multiply and divide. Sure, it goes way up from there but in everyday hobby use, the four operations is about all it takes. You certainly shouldn't be concerned about prior achievement, just build on it as you go along.A lot of people hate math because they do math poorly. And they do it poorly because they hate it. It's a self-defeating circle. I think it starts when the students are introduced to fractions.Maybe hobby electronics can break the circle.BTW, I'm just 75 but I've been retired for more than 17 years. Maybe a little thinking will keep me from growing senile.

author: joesam
author_rank: Contributor
timestamp: February 22, 2021, 09:01:53 pm
content: Quote from: rstofer on February 22, 2021, 08:25:14 pmThanks, You did very well in Your Life , Good for you. I had to go to 72- Because of?? Education-- You get what You earn.I know that.

author: joesam
author_rank: Contributor
timestamp: February 23, 2021, 06:09:07 pm
content: Hey Folks, Just to let You know I Haven't received some of the components to finish my prototype (project) However I did get a different LRD that was more sensitive to visible light. To my surprise , that LRD works as the wiring circuit proposed it would. I added two Solar panels in series ( robbed them from solar garden lights) to the circuit to charge the 14500 battery. I hope to minimize the width and breadth of the assembly and enclose it into Weather proof containers. Smile.