| Electronics > Beginners |
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| lieinking:
I've been sick so I'm not working. I decided to do this as a hobby and am learning mainly from allaboutcircuits.com. My problem is I can't find beginner projects easy enough for me. I've mad a simple circuit with an LED but the next simplest circuit I found is a flashing LED which uses a 555 timer. There's no explanation other than a schematic. Every other online project I see is more difficult. I'm looking for projects that walk you through holding your hand. Where Can I find the simplest projects with good guidance? |
| Wimberleytech:
https://www.forrestmims.com/ |
| Zero999:
--- Quote from: Wimberleytech on February 10, 2019, 10:11:34 pm ---https://www.forrestmims.com/ --- End quote --- Be warned, his books contain some fun errors. Here's a classic one. Assuming both LEDs are equal, LED 1 will never turn on, unless you count the tiny current through the base of Q1. A simple fix could be to make LED 1 red (low Vf) and LED 2 green (higher Vf) (assuming the saturation voltage of Q1 is low enough for it to work) or put a diode in series with it. This would have been an ideal opportunity to explain diode voltage drops and give an example of them being useful. And "Do not subsitute the '339"? WTF? There are only two comparators used. Substitute it for the LM393. I suspect what he meant was, use a comparator IC with an open collector output. Do not substituent with an op-amp IC which has a push-pull output. A short paragraph explaining the difference between open collector and push-pull outputs and ORing would have been a good idea. |
| rstofer:
Take that astable (blinking) 555 LED project and beat it to death with a club! A short definition of astable: Always changing state. not stable in either the on or off state. You can start by building the circuit as given in the description of a project and then research the astable 555 configuration Here's a simple calculator you can use to verify what you see with the various component values http://www.ohmslawcalculator.com/555-astable-calculator Here is a Wiki re: the operation of the chip itself: https://en.wikipedia.org/wiki/555_timer_IC#Astable It is worth knowing how the 555 operates and it is a pretty easy circuit to learn. A capacitor charges up and at some point along the capacitor voltage curve, the internal flip-fflop changes state. The capacitor then discharges and at some point on the way down, the flip-flop changes back again. Plan to spend some time with the circuit, chip description and calculator. As a first project, it is going to take a while to really understand what's going on. The more or less advanced math in the Wiki doesn't help. Use the calculator... Maybe a regular datasheet will help: http://www.ti.com/lit/ds/symlink/lm555.pdf Skim it at first just to find out where various subjects are covered. Then see how the pin description lines up with the circuit you built. Try to figure out what the circuit does with the various pins. Look at page 10 where astable operation is covered. Note that RL is shown in two configurations: The dashed load resistor uses the timer to provide ground to the load that is already connected to Vcc on one end. The plain RL is set up for the 555 to provide Vcc to a load that has one side grounded. Either will work. In fact, I think you can substitute a resistor and LED for both RL configurations. I don't know what voltage you are operating at but if I were doing this with 5V Vcc, I would probably use something like a 470 Ohm resistor and a standard Red LED. At 12V, I might try 1K. Neither configuration is going to overdrive the LED. Or use what your circuit shows. If you spend a solid day playing with the circuit, changing resistor and capacitor values, reading through the documentation and just reflecting on what you see, you will learn a lot. Then tie a monostable 555 to the output of an astable 555. This allows you to define a particular pulse width with the monostable that is independent of the operating frequency of the astable. Within limits, of course. Revisit the project when you get a scope. There is a lot to learn about the capacitor charging voltage that is overlooked in the first pass and, while easy to describe mathematically, really jumps out when you see the capacitor voltage versus output level changes. Then you will really understand the magic! |
| Wimberleytech:
--- Quote from: Zero999 on February 10, 2019, 10:23:35 pm --- --- Quote from: Wimberleytech on February 10, 2019, 10:11:34 pm ---https://www.forrestmims.com/ --- End quote --- Be warned, his books contain some fun errors. Here's a classic one. Assuming both LEDs are equal, LED 1 will never turn on, unless you count the tiny current through the base of Q1. A simple fix could be to make LED 1 red (low Vf) and LED 2 green (higher Vf) (assuming the saturation voltage of Q1 is low enough for it to work) or put a diode in series with it. This would have been an ideal opportunity to explain diode voltage drops and give an example of them being useful. And "Do not subsitute the '339"? WTF? There are only two comparators used. Substitute it for the LM393. I suspect what he meant was, use a comparator IC with an open collector output. Do not substituent with an op-amp IC which has a push-pull output. A short paragraph explaining the difference between open collector and push-pull outputs and ORing would have been a good idea. --- End quote --- LOL...yup. As an author of a technical book...I can appreciate errors. This one seems egregious, however. |
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