Analog Devices Evaluation Board

 My evaluation board has arrived. I'm new to the Analog Devices evaluation ecosystem, and this is evidenced by my purchase of an evaluation board that is meant to be used with their demo platform. The platform costs about $300 on top of the $120 I paid for the ADC eval board. I wish they'd do a razor/razorblade scheme here, but instead I will just put off the $300 investment and make do for now. 

I'm really impressed with the quality of both this board and the its documentation. There are like four external power supply options, two connector types for each input, about two dozen solder point jumpers for various options, some filters, all kinds of shit. Fortunately you're not locked into the AD demo platform, and there is a barrel jack for power (selectable by moving a 0 Ohm resistor jumper) and a pin header to plug in your SPI and other control/data pins. I will be taking this route until I feel rich enough to drop $300 for the platform. 

This is probably wayyyy too much chip for me. It might even be too much chip for my lofty DSP goals. The AD7771 was chosen because it has 8 channels, and has a great sample rate and bit depth for audio (128 kHz/24 bit). It has a low-power mode that samples at 32 kHz, which may be enough for my purpose. I was mostly looking at channel count and sample rate, and I (of course) only skimmed the datasheet. It will certainly work but I definitely could have gotten away with some dead-simple adafruit boards for about the price of this devboard. 

Every mistake presents a new learning opportunity.

If I continue down the path with this chip, I'm going to have to do some fairly serious (for me) PCB design and probably learn more about this level of device than necessary. Oh well. Accidental big boy shit.

I also grabbed a Teensy 4.1 from PJRC, which is their latest ARM-Cortex M microcontroller board. The Teensy came about probably thanks to the popularity of the Arduino platform, and to amateur nerds looking for a little more power. It can be programmed with the Arduino IDE, and while I had a brief thought about picking up Vim again to write code for the thing, I'm going to go ahead and skip that for now. At least for this step, where I need to evaluate the performance of my devices, I'm going to avoid as much additional heavy mental lifting as possible. By the time I get to some serious DSP, I will probably become frustrated with Arduino/Teensyduino and set up a proper toolchain and get into Vim again. Probably will use it for the FPGA as well. Not yet, please.

So the plan for the next few weeks is to set up SPI comms between the Teensy and the ADC, then see about getting first one, then two, then eight signals into the ADC, into the Teensy, and out to a computer for checking out. I'm pretty pumped to listen to the sound, but I'm equally pumped to have a look at detailed frequency spectra for the un-processed tonewheel signals. I want to see the crosstalk, I want to see some harmonics. 

Off to a good start, I suppose.