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Forum Index : Microcontroller and PC projects : PicoMite: Is this expected from quiescent OPTION AUDIO channel
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thwill Guru  Joined: 16/09/2019 Location: United KingdomPosts: 4047 |
Hi folks, In relation to the speaker thread I'm just poking around with my oscilloscope and found this signal on GP6 (and GP7) even without running any program on the PicoMite - is this expected even when the sound is quiescent ?  OPTION AUDIO GP6, GP7 I wouldn't put much faith in the shape of the trace (only its existence) as I'm still using a POS scope with POS probes - the management vetoed my "spending" on a proper one (because I wouldn't use it, and TBH this is the first time I've used my scope in 4 months), but has ackowledged that my upcoming 50th birthday will trump this  .Best wishes, Tom Game*Mite, CMM2 Welcome Tape, Creaky old text adventures |
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| matherp Guru Joined: 11/12/2012 Location: United KingdomPosts: 9139 |
Yes. This is a 50/50 output that generates a steady 3.3V/2 output voltage allowing the wave to swing either side |
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TassyJim Guru Joined: 07/08/2011 Location: AustraliaPosts: 6102 |
A square wave of 50% duty cycle will give you a voltage of 3.3 / 2 after filtering. So, yes, what you see is correct. Jim Edit: my typing is too slow... Edited 2023-03-26 20:38 by TassyJim VK7JH MMedit MMBasic Help |
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| thwill Guru Joined: 16/09/2019 Location: United KingdomPosts: 4047 |
OK, thanks. Best wishes, Tom Game*Mite, CMM2 Welcome Tape, Creaky old text adventures |
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| matherp Guru Joined: 11/12/2012 Location: United KingdomPosts: 9139 |
Direct Digital Synthesis (DDS) signal generation is a technique used in electronics to generate waveforms of different frequencies and shapes. It is based on the precise control of a digital oscillator, which can produce a highly stable and accurate output signal. There are three main components involved in DDS signal generation: A digital signal processor (DSP) or microcontroller, which performs the necessary computations to generate the waveform. A digital-to-analog converter (DAC), which converts the digital signal into an analog voltage. A low-pass filter (LPF), which smooths out the output signal by removing high-frequency noise and harmonics. The DDS technique involves two main steps: A phase accumulator generates a digital representation of the waveform's phase. This value is updated every clock cycle, causing the phase to advance continuously. A lookup table, or waveform table, stores the desired waveform at various phase increments. The DSP reads from this table and outputs the corresponding voltage for each phase value. In the case of the PicoMite the digital-to-analog converter is created by modifying the duty cycle of a 44100Hz square wave By controlling the frequency and amplitude of the output waveform, DDS signal generation can be used in a wide range of applications, such as audio synthesis, signal modulation, and test and measurement equipment. As it is a digital technique, it is highly flexible and can be easily programmed to generate complex waveforms with precise timing and frequency control. Edited 2023-03-26 20:51 by matherp |
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| thwill Guru Joined: 16/09/2019 Location: United KingdomPosts: 4047 |
Thanks Peter, I knew some of this at a very vague level and I appreciate the extra effort to educate me. My query was specifically with regards to whether the signal was expected when MMBasic was not actually requesting any sound be played, I now understand that it is - it is sufficient for OPTION AUDIO to be configured even if not used. Best wishes, Tom Game*Mite, CMM2 Welcome Tape, Creaky old text adventures |
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Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 6814 |
That 'scope's a blinder for the money (38 UKP from Amazon). I'm not going to knock it! It would cost a tenner just for the LCD display. They are really designed to cover just the audio band up to about 20kHz (no matter what it says elsewhere) and they aren't too bad for that. Anything higher than that is a bonus. :) Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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stanleyella Guru Joined: 25/06/2022 Location: United KingdomPosts: 2134 |
I got 2 broken ones. Don't try reflashing them with new firmware :( I got a hantek 6022b usb scope for £50 and it's spec is optimistic but it's handy with a laptop and the open source win software. I bet someone has done a pico mite scope that's faster than the lcd scopes. |
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