Revision 0.2 is under development. Hardware issues with the previous version are corrected (added load capacitors and a battery backup to the RTC). I’m also reducing the footprint of the parts as much as possible, moving towards more SMD parts and replacing the barrel connector for USB.
As for major design additions in this revision, I am adding a haptic driver IC to enhance the experience in haptic mode. I’m also replacing the existing beeper with a speaker and will add an option to have the clock audibly read out the time in English using voice clips stored on a flash chip. The button to trigger the device will be replaced with either a non-contact light-based sensor or a capacitive sensor. The preliminary circuits are designed in schematic but I’d like to run a few electrical tests before laying out the board. After that I’ll layout the board and design a new case, then order the parts and PCB to put it all together.
Here are some details about the new electrical features.
Because the vibration pattern for reading the time digit-by-digit is complex (especially at first), it’s important that the vibrations being generated are of the highest quality. Crisp vibrations will make it easier to discern individual haptic pulses. I’m looking at the TI DRV2605LDGSR IC, which supports many types of haptic patterns and has drivers to overdrive and brake the motor for faster starts and stops. The chip is expensive though ($5.56 CAD) so it may be worth revisiting a more simple H-Bridge again to see if the performance is comparable.
The audio clock function requires two components – the first being the audio system comprising of a DAC, an amplifier, and a speaker.
Voice data will be stored in an external Flash chip in wav format. Given that mono, 12 bit wav files are be 60kB/s and we need a couple dozen seconds of sound (for each number, tens, teens, and words like “pm”, or “oclock”), a flash chip with a capacity between 1 and 4MB should be used. Flash chips, while slower and less flexible than EEPROMs, seem to be cheaper especially at high capacities.
After using my v0.1 No-Eye Clock for a few months, I realized that I didn’t really like the button to activate the clock. It was awkward to push the button and hold the case in a way that was easy to feel the haptic vibration, and was sometimes hard to find the button in the middle of the night. I’m going to try out an IR/photo transistor sensor – when a hand is nearby, the reflected IR will activate the phototransistor and send a pulse to the GPIO. The IR LED needs only by pulsed every few sensors rather than stay on continuously, which reduces the power consumption of this sensor.
Thanks for reading! Will continue to update!