Handy little circuits that you can build.

[@maxximumb]

I never thought about using a flashing LED like that. Excellent idea. Thanks.

[@sayantanmaiti2513]

thanks bro...the 4N35 was useful..I've been searching for its application for a few days and you showed me today

[@j.clowers7223]

Awesome lesson! More more more....

[@alibehrouz9833]

Handy little circuits! as always your job was great thanks

[@cndbrn7975]

Thanks ..

[@0033mer]

You're welcome!

[@gabejasso1747]

Hi 0033mer, I have a question: since current flows from a battery or power source from negative to positive, why is I that we attach a series resistor to the positive (anode) lead of the led? It seems like the cathode should be protected first since that is the side of incoming current. I'm confused.

[@0033mer]

DC current actually flows from positive to negative and electron flow is from negative to positive. The direction of current flow has no bearing on where the series resistor is placed. In a series circuit the current is the same no matter how many components are involved. Placing the resistor on either side of the LED is ok.

[@thanhavictus]

Would you recommend this flashing LED as a controller for effectively acting as a 2hz PWM for slowing down a DC motor?

[@0033mer]

You cannot change the duty cycle of the LED flasher so a simple circuit using a CD4093 would work out better. kzbin.info/www/bejne/o5usppWAmrmFr7s

[@mikex691]

Excellent!!!

[@UpcycleElectronics]

Thanks... and sold... I've got to order me a flashing led. Suddenly I realize they are slightly more useful instead of just plain annoying. I've played with that JFET current circuit awhile back just for fun. It gets a little more resistant to input change if you put 2 JFETs in series. In a pinch, N channel JFETs are used inside almost all electret microphones. It's probably the most common place to find one, if your willing to ruin a cheap mic to pull one out. I've build a little guitar preamp using one just to compare it to a few other classics like the 2N5457 and J102 (IIRC the correct part numbers from memory ;) I have a bit of a request for an Engineer. I've been trying to understand the different ways to divide and measure a frequency with a simple 8 bit MCU. There is a circuit related to the Open Source AVR Transistor Tester project. This auxillary circuit uses a few logic ICs to test "high" and "low" frequency crystals. The circuit uses a CD4011 NAND Gate (for "low" only), that feeds into a 74HC4052 multiplexer (that is the "high" input as well). The first 74HC4052 is in series with a 74HC4060 -14-stage binary ripple counter with oscillator, that is in series with another 74HC4052 multiplexer This is then connected to an MCU pin and interpreted in software. I'll try to upload a picture shortly, just in case anyone wants to see what I'm talking about. I'm not asking anyone to explain the circuit, build it, or anything like that. I want to better understand frequency multiplication and division. I need more fluid concepts on a practical and simple level from someone who knows how to explain things visually while keeping it 5-10 minute simple. That's a unique skill I'm learning to value. I've been flipping through The Art of Electronics, done a few web and forum searches but I keep going down rabbit holes of information where I need to research lots of background info to understand the subject as it is explained. I haven't played with a lot of logic IC's, I'm learning about AVRs at the moment, and I have no real experience with precision frequency devices. So from that perspective, what is frequency division? What are the different topologies/approaches/limitations, with simple hardware? I'm surprised this information seems so difficult to figure out. I've put together a colepitts oscillator that Allen showed on his W2AE channel that I use with my Rigol scope, but I'm trying to understand how to build more complex circuits. Are the IC's used in the circuit mentioned specifically important or is it simply a buffer, multiplexer, counter, multiplexer kind of thing? Is there some easier way to do this through an integrated circuit? -Jake

[@UpcycleElectronics]

Link to image of the frequency divider circuit mentioned lh3.googleusercontent.com/-Azly5ePhc6s/WfQTjRX2K_I/AAAAAAAAAf4/mV44rNrQ2EsKwKkQH-g39Jty-vtdswbrgCHMYCw/s640/Screenshot_2017-10-27-20-29-32.png

[@0033mer]

To divide a clock frequency we use the D flip-flop in toggle or divide by two as a building block. We can cascade them to divide by a large number as seen in the 4024, 4040, 4028 and 4060 ripple counters These counters can only divide by even integers. To divide by odd numbers you can use a Divide by N 4018. To multiply a frequency we use PLL ( Phase Locked Loop ) like the 4046. W2AE has a good video on PLLs. With microcontrollers being quite common today the way to divide/multiply clock frequencies is by using DDS ( Direct Digital Synthesis ) www.adafruit.com/product/2045