openbench:fgen
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openbench:fgen [2007/04/13 04:05] ladyada |
openbench:fgen [2007/12/03 16:36] geekabit |
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| A completely open design for a function/waveform generator: hardware, firmware, software | A completely open design for a function/waveform generator: hardware, firmware, software | ||
| - | for more info, read about [[OpenBench]] | + | for more info, read about [[start|openbench]] |
| For collected links, try [[http://del.icio.us/ladyada/dds|DDS link on delicious]] and [[http://del.icio.us/ladyada/fgen|Function Gen link on delicious]] | For collected links, try [[http://del.icio.us/ladyada/dds|DDS link on delicious]] and [[http://del.icio.us/ladyada/fgen|Function Gen link on delicious]] | ||
| ====== Notes & stuff ====== | ====== Notes & stuff ====== | ||
| + | |||
| ===== Design constraints ===== | ===== Design constraints ===== | ||
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| * Sine wave | * Sine wave | ||
| * Square wave (with variable PWM) | * Square wave (with variable PWM) | ||
| - | * Triangle wave | + | * Triangle wave (with variable PWM?) |
| * Sawtooth (possibly a modification of triangle wave???) | * Sawtooth (possibly a modification of triangle wave???) | ||
| - | * arbitrary waveform (sync, envelopes, etc) | + | * Arbitrary waveform (sync, envelopes, etc) |
| Frequency range: | Frequency range: | ||
| * 1 Hz -> 100 KHz required (must cover audio ranges) | * 1 Hz -> 100 KHz required (must cover audio ranges) | ||
| * 1mHz -> 10MHz is ideal (digital/analog ranges) | * 1mHz -> 10MHz is ideal (digital/analog ranges) | ||
| + | |||
| + | Output capabilities: | ||
| + | * 50 ohm/inf impedance | ||
| + | * 1mv -> 10V amplitude | ||
| + | * 0 -> 10V DC offset | ||
| + | * trigger output | ||
| USB control? Panel control? Both? | USB control? Panel control? Both? | ||
| Line 30: | Line 37: | ||
| 100mA is not a bad current capability to shoot for | 100mA is not a bad current capability to shoot for | ||
| - | |||
| - | 50 ohm/inf impedance? | ||
| PCB is doublesided, 10/10 rule | PCB is doublesided, 10/10 rule | ||
| Line 50: | Line 55: | ||
| * 100 KHz or higher (must cover audio ranges) | * 100 KHz or higher (must cover audio ranges) | ||
| * 1mHz -> 10MHz is ideal (digital/analog ranges) | * 1mHz -> 10MHz is ideal (digital/analog ranges) | ||
| + | |||
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| Direct-Digital-Synthesis, currently popular. Basically: wavetable + 24 or 32 bit adder and sampling above nyquist to get precision waveforms. | Direct-Digital-Synthesis, currently popular. Basically: wavetable + 24 or 32 bit adder and sampling above nyquist to get precision waveforms. | ||
| - | |||
| * Pros: digital, precise, no PLL needed | * Pros: digital, precise, no PLL needed | ||
| * Cons: hard to get high frequencies because of oversampling | * Cons: hard to get high frequencies because of oversampling | ||
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| For CPLD, 100MHz PLCC (44 or 68) either XC9500 (xilinx) or MAX7000 (altera) | For CPLD, 100MHz PLCC (44 or 68) either XC9500 (xilinx) or MAX7000 (altera) | ||
| - | **Idea #3**: Hand-roll the adder code into an AVR microcontroller, and use onboard memory. Lots of examples: [[http://www.scienceprog.com/avr-dds-signal-generator-in-line-asm-explained/|9 Cycles of ASM w/LPM]] (note: can't we do this in 8 cycles by using LD? just make sure we have an AVR with more than 256b of RAM) | + | **Idea #3**: Hand-roll the adder code into an AVR microcontroller, and use onboard memory. Lots of examples: [[http://www.scienceprog.com/avr-dds-signal-generator-in-line-asm-explained/|AVR generator]] or [[http://www.myplace.nu/avr/minidds/index.htm|Jesper miniDDS]] (note: can't we do this in 8 cycles by using LD? just make sure we have an AVR with more than 256b of RAM) |
| * Pros: ultra-cheap/simple | * Pros: ultra-cheap/simple | ||
| * Cons: 8 @ 20MHz -> low frequency output (20M/16samples/8cycles = ~150KHz), 8bit resolution | * Cons: 8 @ 20MHz -> low frequency output (20M/16samples/8cycles = ~150KHz), 8bit resolution | ||
| Other possibilities include going with an SX instead of AVR: SX28 can be clocked up to 75MIPS (maybe give us 500KHz...but will draw an insane 100mA from 5V. jesus!) | Other possibilities include going with an SX instead of AVR: SX28 can be clocked up to 75MIPS (maybe give us 500KHz...but will draw an insane 100mA from 5V. jesus!) | ||
| + | |||
| + | **Idea #4**: A combination of idea #1 and idea #3. Take a simple AVR that is able to calculate waveforms, but not in realtime. Load the wavetable in some external RAM, and clock it at the desired speed. | ||
| + | * Pros: high frequency, adjustable waveform | ||
| + | * Cons: complex | ||
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| * Pros: simple, regulated, ultra compact | * Pros: simple, regulated, ultra compact | ||
| * Cons: expensive, noisy | * Cons: expensive, noisy | ||
| + | **Idea #4b** Build your own DC/DC converter, a bit like [[http://spritesmods.com/?art=ucboost&page=2|sprite_tm]] did. Have the processor generate the PWM needed for the converter. | ||
| + | * Pros: cheap, same as idea #4 | ||
| + | * Cons: noisy | ||
| + | |||
| + | ====== Planned versions ====== | ||
| + | |||
| + | |||
| + | ===== Inexpensive kit ===== | ||
| + | |||
| + | ==== Power ==== | ||
| + | USB and/or external power (9VDC) | ||
| + | |||
| + | Single output, +12V max (maybe -12V too). | ||
| + | |||
| + | Boost converter: LT1610 will give +12V @ 1.2MHz switching freq. Has 8V max input so must clamp input. ugh. | ||
| + | |||
| + | For isolation, use wall wart that provides 5->9VDC | ||
| + | |||
| + | ==== UI ==== | ||
| + | 2x16 LCD and some buttons & rotary encoders for UI. | ||
| + | Maybe an 'm88? at 12MHz does the UI work and USB nonsense. (USB "serial" (or raw) interface using USBtiny.) and sends just raw serial/spi commands to DDS chipset | ||
| + | |||
| + | |||
| + | ==== Chipset ==== | ||
| + | DDS done by dedicated chip probaby Atmega48 running @ 20MHz | ||
| + | |||
| + | DAC is DAC0800 (?) | ||
/home/ladyada/public_html/wiki/data/pages/openbench/fgen.txt · Last modified: 2016/01/28 18:05 (external edit)
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