Hello,
Oh no, not another clock...
My first standalone MSP430 project and also my first project to
be programmed "in circuit", and a soldering exercise for the TSSOP housing
A tiny LED clock. It is minimalistic by all means:
-a TSSOP G2452, no other IC
-only one button to set the time
-a dumb 4 digit white LED 7 segment display, https://www.sparkfun.com/products/11409
-a PCB size of 25mm x 25mm
-extremely low power
Wanted to find out whether I can use the TSSOP with my usual home made setup,
that is Eagle, Deskjet printer, photosensitive base material, UV-lamp, develop,
the ugly FeCl3 etching, and then hand-solder.
The PCB is single sided of course.
I use the lauchpad for programming.
The white LEDs of the display are pretty bright at their nominal current.
I wanted something low power and just enough brightness to see the time in the
middle of the night with darkness-adapted eyes.
So at 4:30 in the morning, the display is much more useful than an LCD.
The whole thing draws around 0.3- 0.5mA, LEDs included.
CPU runs at 1Mhz, but is in LPM3 most of the time, even though the poor thing has
a restless sleep: it has to wake up 512 times a second, to do the multiplexing.
At this low current there are quite a few options for a power supply, I considered
- 2 AA cells; would run around half a year
- something solar, with supercap
- I ended up with direct AC supply via a capacitive dropper, 4700pF mains rated film
cap. Where I live, plugs are polarized, so I know which one if life and which one
is neutral. Still I think that this would not be street-legal without double insulation
housing.
Overall I calculated 2milliwatt total power consumption, probably the lowest of
any mains powered clock.
If anybody is interested, I might bring schematic and software into
human-readable form.
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Tiny low power LED clock
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