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Im designing an analog audio amp with a 6 band analog equalizer controlled via a 7" LCD touch screen. Im wanting to preform a real time 2048 point FFT and display it on the screen in some kind of visual animation. The equalizer will have digipot that will be on a SPI bus. I was shooting for a all in one solution. Also some kind of cheap dev board to prototype with is a must. Below are the requirements that I have come up with.

  • min 43 GPIO
  • min 50Mhz clock
  • min 1 10 bit resolution ADC
  • FFT capability

This is my first large design project and I'm a little overwhelmed with the size of the market. Was looking at the Stellaris made by TI, but it turns out that the chip is still in experimental phase and not available for test are distrobution. I was thinking about possible desoldering the chip and putting it on my own board but was concerned that the chip may be stressed to much. Any input are advice would help a bunch.

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In my experience, TI is super friendly when it comes to nailing down which part you need (you may even get them to send you a sample). I'd try giving them a ring and see what they suggest. – sacredfaith Apr 8 at 22:10
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FFT isn't normally a hardware feature. There are plenty of FFT libraries you can use, some/most requiring a Floating Point Unit, which is what you might really need. As for the GPIO, do you need that many? For Leds or what? What about charlie/multiplexing leds in that case? Since you are already using spi, you could just use spi port expanders if you really need that many gpio. – Passerby Apr 8 at 23:34
The LCD screen that i'm interfacing with requires a minimum of 25ish pins to interface with it fully. then tack on 2 pins for an analog source select, an 3 pins for CE lines on the SPI bus plus the data line and clock and latch, then the ADC line. So the total comes to around 30ish and i want some room to add features if desired. – jason lamberet Apr 9 at 2:27
There is a plentitude of LCD drivers. You can save yourself lots of GPIOs, a lot of trouble with coding and tracing, if you use one of these. – Jonny B Good Apr 9 at 7:17
@Passerby - audio DSP (especially with only 10 bit input) is typically reasonable on a platform without an FPU. That said, cortex M4's are pretty cheap now. – Chris Stratton Apr 9 at 15:19
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4 Answers

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Aside from Ti's Stellaris family with the Stellaris Launchpad, other Arm/Cortex families will fit the bill. Only other one I know of is STM's STM32 F3 series Cortex-M4, with the Discovery dev kits like the STM32F3DISCOVERY. Basically competing products, but the STM32F303VCT6 is available for individual purchase on Digi-key and such (At 9 bucks in single quantities, sometimes just using the dev board for your project might be a better option). Any of their discovery boards will do what you need for about the same price.

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Thanks you for the suggestion I will definitely investigate that option. – jason lamberet Apr 9 at 3:44
If you are going with STM32F3, you might want to look at the 37x's instead of the 30x's as the former have a sigma delta ADC with configurable gain, which may be more applicable to an audio project. That would require a custom board, but it's worth getting the F3 discovery anyway to use as a cheap SWD programmer if not application platform. – Chris Stratton Apr 9 at 15:22
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There are a number of cheap dev boards available that could meet your rather low requirements. Are you willing to run a high level OS on your system, such as embedded linux? If so, TI's OMAP family would be a great decision. The very popular Beagleboard would be a great dev board to get started on.

http://en.wikipedia.org/wiki/BeagleBoard

If you are looking for a bare metal solution the OMAP could still work but it's much less supported and their a much less resources available.

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This would however be quite a bit more complex, and multiply the hardware cost by a factor of between 3 and 15. – Chris Stratton Apr 9 at 15:23
The OMAP3530 on the BeagleBoard are BGA packages and normally require multiple layer boards. Not very friendly, compared to the Stellaris LQFP (Quad Leaded Package). OP wants to use the chip on his own custom board, without the rest of the dev kit. – Passerby Apr 9 at 21:23
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If you want something really cheap, I would consider the Freescale Freedom platform. Take a look here: Freedom

This is built with a cortex-M0 ARM microcontroller. This one can run up to 48 MHz, so I could'nt say if it's enough for your application. There is plenty of FLASH and RAM to do some kind of FFT math, and besides, this is a 32-bit CPU.

If you are willing to put some more money in this project, go ahead and pick the Freescale Tower system. It is very versatile and you can opt for several microcontroller boards to act as its brain. Freescale Tower. This is a modular development system, and for your needs I would recommend selecting a board with a ColdFire+ mcu (16bits) or a Kinetis (32bits) to suit your tastes.

Also, some of the ColdFire+ and Kinetis mcu have hardware dsp capabilities, so it really could help your FFT routines. Look for the ones with a MAC module.

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