After the flurry of activities in recent weeks on a previous post (thanks guys!) I finally went back and worked on the synth project some more. Some time ago I had already created a simple MIDI input and output circuit on a stripboard that the Discovery board could sit on. This would allow me to play notes or adjust parameters from any standard MIDI controller or the PC. The hardware setup for this was quite simple using a 6N137 optocoupler, which gets its 5V supply voltage directly from the 5V rail of the Discovery board. Since the output of the optocoupler is just an open drain, I didn’t even have to worry about any level shifting and directly connected it to the USART2 RX input on pin PA3, which I configured with an internal pull-up. (I have yet to test the output side, which is coming from USART2 TX on PA2 and goes to an external MOSFET.)
One way in which it’s easy to tell that I’m still relatively new to the whole electronics and microcontroller hobby is by the amount of new developments in this area I tend to miss until much later. One of those is the release of the STM32F4-Discovery evaluation boards from ST Microelectronics. While I was aware of some of their other STM32 ARM based boards (and had considered buying one of them), this particular one had escaped my notice until a few weeks ago. But why is this such a big deal, you will ask. Well, the big deal, for me at least, is that the STM32F4-Discovery comes with a microcontroller and a few peripherals that fit perfectly with my particular interests.
So what do you get with an STM32F4-Discovery board? At the heart of the board is an STM32F407VGT6 microcontroller. That’s a 32-bit ARM Cortex-M4 based microcontroller with 1MB onboard Flash and 197kb RAM, which can run at up to 168 MHz. Importantly for me, it is classified as a “Digital Signal Controller”, because the Cortex-M4 core is essentially a Cortex-M3 core with added DSP instructions. While it certainly wont be able to compete with dedicated DSP devices, it should still provide a decent amount of computing power for moderate DSP applications. What’s also nice is that every single one of the 100 pins of the LQFP100 packaged device is routed to two headers on the board, although only about half of them are still unused. The other pins are already connected to some of the onboard peripheral devices.
The other devices on the board are the ST-LINK/V2 section at the top, which is used to program the device, but can also be used stand-alone to program and debug external devices. This alone makes the STM32F4-Discovery a very interesting board. Even more important for me, however, was the fact that it includes am onboard DAC with headphone amplifier (a Cirrus Logic CS43L22) and a headphone jack of course. It also includes a digital microphone (ST MP45DT02), a MEMS accelerometer (ST LIS30DL) and a few LED’s, 2 push-buttons and a micro-AB USB connector. This should make it very easy to try out some sound-related applications and other little things (how about changing cutoff frequency and resonance of an audio filter by tilting the board?)
So last weekend I ordered the STM32F4-Discovery from Farnell/Element14 for just under 10 Pounds (+VAT). I filled my 20-Pound minimum order with a few 8/16-bit micros (several TI MSP430’s and an Atmel AVR), which should come in handy as support chips for slightly more complex prototypes. The order arrived 2 days later, but I haven’t had much time to play with the board yet (partly due to extreme weather conditions here). However, I’m very excited to get my proverbial hands dirty with this little board.