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Basic Electronics » Oscilation circuits
March 29, 2011 by Hexorg |
Hello everyone, I've come up together with a few circuits that will produce an oscillating signal with variable frequency. Unfortunately, I couldn't remember some formulas, and I don't have the time right now to look for them online. You are more then welcome to correct me, and add anything. :) Here we go. Manual starting Wien-bridge sine oscillator:
Self starting Wien-bridge sine oscillator using zener-diodes:
Self starting Wien-bridge sine oscillator using JFET:
Triangular-wave oscillator:
Square-wave oscillator:
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March 30, 2011 by Ralphxyz |
Nice Stan, thank you. The op-amp is a 741 or equivalent correct? V2 would be a negative power supply correct? Now some circuits driven by the mcu would be interesting. Pin change high/low and PWM signals. Thanks to the formulas I should be able to work out the parameters so that I can learn how to read/understand my oscilloscope. I have my Forrest Mims Electronics Tablets with similar circuits but I like having them here. Ralph |
March 30, 2011 by Hexorg |
Yes, op-amp is 741 (those guys are really useful). Yes, V2 is negative, sorry I didn't mark them, but generally on a DC power supply symbol the side that ends with a longer line is positive, and the side that ends with a shorter - negative. If you want something cool, driven by the MCU, try this: Integrator:
Differentiator:
Digital to Analog converter: This can be a really useful circuit. Not too expensive either - for an N-bit converter you need 1 op-amp and N+1 resistors. It just works as weighted summing amplifier. Resistor 2R is twice as resistive as R, 4R is 4 times, and so on. You HAVE to keep this pattern.
The whole expression is (D0 - voltage at LSB; D8 - voltage at MSB):
Note the "-" at the beginning. If you want positive output, just pass it through an inverting amplifier. The output of this will be composed of a series of "steps" of voltages, instead of smooth analog signal, this is known as alaising. To smooth out the signal, (operation known as anti-alaising), just connect the output of the DAC to an integrator mentioned above. |
March 30, 2011 by Hexorg |
Oh! it's off-topic, but I'm getting the same scope XD |
March 30, 2011 by bretm |
The main problem with that type of DAC is that you need very accurate resistors. In order for R and 128R to be in the same ratio, you need better than 1% tolerance, or else test a lot of resistors to find ones that match the best. If you actually want to build this circuit for use with the MCU, I'd stick to 6 or fewer bits (stop at 32R). |
March 30, 2011 by bretm |
(or use a resistor ladder) |
March 30, 2011 by Hexorg |
bretm, Yea you are right, if you really need a precise DAC. If someone just wanted to test their oscilloscope with it, or just to play around, that'd work with any 10% tolerance resistors :) |
March 30, 2011 by bretm |
But if you don't need a precise DAC, you can just use 5 bits instead of 8 in which case 10% is appropriate anyway. |
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