A Useful General Purpose Oscillator.
Posted: Sun May 31, 2020 3:28 pm
Working with and/or building electronic circuits requires a number of 'tools'. Aside from the usual cutters, soldering irons and so on, more active 'tools' are required. These include a multimeter, power supplies, an oscilloscope...and so it goes on.
A source of basic signals is always handy, just sine and square say. I've been using for years a rather crappy signal generator which really could do with replacing. A decent and moderately accurate signal generator doesn't come cheap. But here's my embryonic idea...
There's a small module available from many internet traders called a HC-SR08. This is a complete sine and square waveform generator which outputs both simultaneously at any frequency between 0.0291Hz and 40MHz in 0.0291Hz increments. The average price is around US$16-20.
However it needs an interface to translate what you and I can understand to it's logic instructions.
The increment is derived from the crystal oscillator frequency (125MHz) divided by 2^32, or 0.0291Hz. The inverse of 0.0291 is 34.3597..., so if you wanted 1000Hz, multiply that by 34.3597... then fire it at the HC-SR08 module and you'll get 1000Hz out.
Well, actually you won't, it'll be 999.9924Hz as 1000 will not divide by 0.0291 and yield an integer result. The error is -7.6ppm (parts per million) less than 0.001%. I think I can live with that! At the price these are the error in the crystal oscillator frequency is probably greater than that. So here's my draft (or is that daft) idea...
The micro does all the multiplication and translation, ASCII digits in - frequency out, You could use a PC with a terminal program to set the frequency or a keypad that generates ASCII - few of them around though. The micro is in a 14-pin DIP package, so it's no harder to wire up than a 7400.
The sine wave distortion is quoted as -50db (0.3%) at 40MHz and improves at lower frequencies. The reason for the mention of "To LF Generator" is if you need a low-distortion source for testing or designing Hi-Fi gear...I'll probably not bother.
Anyway, more to come in due course...I plan to also compliment this with a True RMS meter. Some multimeters say they they are True RMS, but look at the specs carefully, often they become inaccurate at quite low frequencies, say above 1000Hz. They're primarily designed to just measure 50 or 60Hz, not audio or higher. There are exceptions (some Flukes), but at a price!
Steve A.
PDF for the HC-SR08 attached...
A source of basic signals is always handy, just sine and square say. I've been using for years a rather crappy signal generator which really could do with replacing. A decent and moderately accurate signal generator doesn't come cheap. But here's my embryonic idea...
There's a small module available from many internet traders called a HC-SR08. This is a complete sine and square waveform generator which outputs both simultaneously at any frequency between 0.0291Hz and 40MHz in 0.0291Hz increments. The average price is around US$16-20.
However it needs an interface to translate what you and I can understand to it's logic instructions.
The increment is derived from the crystal oscillator frequency (125MHz) divided by 2^32, or 0.0291Hz. The inverse of 0.0291 is 34.3597..., so if you wanted 1000Hz, multiply that by 34.3597... then fire it at the HC-SR08 module and you'll get 1000Hz out.
Well, actually you won't, it'll be 999.9924Hz as 1000 will not divide by 0.0291 and yield an integer result. The error is -7.6ppm (parts per million) less than 0.001%. I think I can live with that! At the price these are the error in the crystal oscillator frequency is probably greater than that. So here's my draft (or is that daft) idea...
The micro does all the multiplication and translation, ASCII digits in - frequency out, You could use a PC with a terminal program to set the frequency or a keypad that generates ASCII - few of them around though. The micro is in a 14-pin DIP package, so it's no harder to wire up than a 7400.
The sine wave distortion is quoted as -50db (0.3%) at 40MHz and improves at lower frequencies. The reason for the mention of "To LF Generator" is if you need a low-distortion source for testing or designing Hi-Fi gear...I'll probably not bother.
Anyway, more to come in due course...I plan to also compliment this with a True RMS meter. Some multimeters say they they are True RMS, but look at the specs carefully, often they become inaccurate at quite low frequencies, say above 1000Hz. They're primarily designed to just measure 50 or 60Hz, not audio or higher. There are exceptions (some Flukes), but at a price!
Steve A.
PDF for the HC-SR08 attached...