I know it’s been a bit since I’ve done an update but I wanted to put it out there – the first public revision of the CREMA firmware!! It’s being released under the Creative Commons Attribution-ShareAlike License so as to provide a significant amount of freedom with respect to what people can do with it.
So I’ve soldered up the first CREMA Revision A board and spliced it into Silvia’s internals. It works exceedingly well except for a few minor hiccoughs that I tracked down and worked out. To start, the CREMA board was spontaneously aborting during brew cycles, and it took the better part of 24 hours to hypothesize, test, and revise. It turns out it was caused by two problems: one was hardware related (in Silvia’s native wiring), and the other was software (duhhhhhhhh ….).
As it stands, Silvia is wired to power the solenoid valve when the brew switch is thrown – both line and neutral wires are switched. The only place to splice in the brew switch line voltage is at the point where the solenoid LINE voltage (orange wire if you’ve cracked your Silvia open) meets the switch. Unfortunately these solenoid valves act like MASSIVE inductors so every time the brew switch was thrown and then powered off, a residual current would discharge through the line voltage sensor – in short it didn’t turn off promptly. However I fixed this by bypassing the switch and tying the neutral lines directly together (keeping the LINE voltage switched) to allow for a more favourable current discharge path. Hardware issue resolved.
The software issue was a silly one – I forgot that I had included some ‘press ok to go to next step’ sort of steps in the code for testing purposes. The display keypad kept jiggling with the vibrations from the pump and tripping the OK state >_<. Sigh. Commenting out the offensive lines of code resolved the issue.
I need to finish writing the code now for the alarm and RTC although that's trivial. I also need to tune the PID parameters to get it to stabilize (rather than over or undershooting the target). The menu system and navigation is also fairly well complete. I'm pretty content with how I've coded the menu. To store a multidimensional menu system (that is, one with sub menus and sub menus etc.) with an excess of 80 menu elements (each with screen contents and associated button functions) in SRAM is not possible when you have a total of 2500 bytes available. So everything got pushed into program memory instead. Effectively the number of elements in the menu has no footprint in SRAM - ^_^.
On how it tastes ... I've pulled a few shots using the CREMA board, and so far, I've noticed two things: the flavours are far more robust than I would have ever imagined, and the temperature is far more consistent than I would have ever imagined. It's amazing the difference a PID makes. Right now I'm drinking Femenino Columbia Cosurca, a single origin from Dark City Coffee here in Toronto – and while it was super tasty before, it’s beyond this world now.
So I’ve finished the board for CREMA Revision A – Prototype 1. It’s a beaut!
I’ll have it printed and wire it up. I can’t wait.
Unfortunately due to size constraints, all components are surface mount (to the exclusion of the Molex headers etc.) Fair warning: unless you have a reflow oven, soldering this board will not be for the faint of heart. There are no components smaller than a 0603 resistor so if you’re good with that, then this will be a breeze!
The prototype has the following functions / features:
Dual P.I.D. Boiler Control (PWM based)
Dual PT100 RTD Temperature Sensors with 24-bit resolution providing 0.05°C temperature accuracy
Single Pump Control (PWM based: allows for pressure profiling)
16×2 Display Module
Onboard real-time clock with two alarms
Bluetooth or WiFi (using Electric Imp) connectivity for remote control
Some of the design details include:
Onboard 5V 2,000mA power supply with resettable fuse and ESD protection
Faston Quick Connect tabs to be compatible with internal wiring of many espresso machines
Power indicator LEDs for Boiler A, Boiler B, and Pump solid state relays
Zero-crossing solid state relay to allow precise control of vibratory pumps
Line-voltage sensors to determine switch states without requiring any special wiring
Molex connectors with gold-plated pins to minimize connection problems
Once I work out any underlying bugs, I’ll firm-up the firmware and make a public release of the board.
One of the biggest limitations within the Arduino IDE is the inability to render float types using sprintf() or some other print() family function. For the sake of sketch size, these functions were largely stripped down of their ability to handle float types in favour of a float-to-string conversion function for those who needed it. Anyone who does use sprintf() with a float type will be met with a '?' in place of their float. However this is not to say that the Arduino IDE cannot generate sketches capable of handling floats! In fact, the AVR compiler that the Arduino IDE uses supports floats in sprintf() – just not by default. So we need to instruct it to do so.
I’ve written up some (pretty simple) instructions that you can follow to prepare your own Arduino IDE that will support float types with sprintf():
Navigate to the following file and open it using your favourite text editor (you might have a slightly different file structure depending on your operating system): /app/app/src/processing/app/debug/Compiler.java
Search for the following line of code: "-Wl, --gc-sections"+optRelax,
Replace that line of code with: "-Wl,-u,vfscanf,-lscanf_flt,-u,vfprintf,-lprintf_flt,--gc-sections"+optRelax,
Save the file and continue with the rest of the build process.
If all goes well, you should now have a fresh Arduino IDE built from the latest source code that supports floats in sprintf(). No more nasty ‘?’ :). You’ll notice however that even basic sketches are rather large in size (~10kb). However this is a tradeoff that you must be willing to make if you want sprintf() with float support.
I hope this helps everyone – I know I certainly appreciate having float support.